Fix typo

Instead of using `kamal envify` to generate the .env file, we now assume
that it will be in place for us.

Options in place of `kamal envify`:
1. Pre-generate the .env file
2. Create the env file in the `.pre-init` hook
3. Log into a secret store/check you are logged in in the pre-init hook
   Then use .dotenv command and variable substitution to interpolate the
   secrets.

.github/workflows/ci.yml

@@ -1,21 +1,42 @@
 name: CI
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - main
+  pull_request:
 jobs:
+  rubocop:
+    name: RuboCop
+    runs-on: ubuntu-latest
+    env:
+      BUNDLE_ONLY: rubocop
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      - name: Setup Ruby and install gems
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 3.3.0
+          bundler-cache: true
+      - name: Run Rubocop
+        run: bundle exec rubocop --parallel
   tests:
     strategy:
       matrix:
         ruby-version:
-          - "2.7"
           - "3.1"
           - "3.2"
-        continue-on-error: [false]
+          - "3.3"
-
+        gemfile:
+          - Gemfile
+          - gemfiles/rails_edge.gemfile
     name: ${{ format('Tests (Ruby {0})', matrix.ruby-version) }}
     runs-on: ubuntu-latest
-    continue-on-error: ${{ matrix.continue-on-error }}
+    continue-on-error: true
-
+    env:
+      BUNDLE_GEMFILE: ${{ github.workspace }}/${{ matrix.gemfile }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - name: Install Ruby
         uses: ruby/setup-ruby@v1

.github/workflows/docker-publish.yml

@@ -0,0 +1,55 @@
+name: Docker
+
+on:
+  workflow_dispatch:
+    inputs:
+      tagInput:
+        description: 'Tag'
+        required: true
+    
+  release:
+    types: [created]
+    tags:
+      - 'v*'
+
+jobs:
+  build-and-push-image:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: read
+      packages: write
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v3
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v2
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+      -
+        name: Login to GitHub Container Registry
+        uses: docker/login-action@v2
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+      - name: Determine version tag
+        id: version-tag
+        run: |
+          INPUT_VALUE="${{ github.event.inputs.tagInput }}"
+          if [ -z "$INPUT_VALUE" ]; then
+            INPUT_VALUE="${{ github.ref_name }}"
+          fi
+          echo "::set-output name=value::$INPUT_VALUE"
+      -
+        name: Build and push
+        uses: docker/build-push-action@v3
+        with:
+          context: .
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: |
+            ghcr.io/basecamp/kamal:latest
+            ghcr.io/basecamp/kamal:${{ steps.version-tag.outputs.value }}

.gitignore

@@ -1,4 +1,5 @@
 .byebug_history
 *.gem
 coverage/*
-.DS_Store
+.DS_Store
+gemfiles/*.lock

.rubocop.yml

@@ -0,0 +1,2 @@
+inherit_gem:
+  rubocop-rails-omakase: rubocop.yml

CODE_OF_CONDUCT.md

@@ -0,0 +1,41 @@
+# Contributor Code of Conduct
+
+As contributors and maintainers of the Kamal project, we pledge to create a welcoming and inclusive environment for everyone. We value the participation of each member of our community and want all contributors to feel respected and valued.
+
+We are committed to providing a harassment-free experience for everyone, regardless of gender, gender identity and expression, sexual orientation, disability, physical appearance, body size, race, age, or religion (or lack thereof). We do not tolerate harassment of participants in any form.
+
+This code of conduct applies to all Kamal project spaces, including but not limited to project code, issue trackers, chat rooms, and mailing lists. Violations of this code of conduct may result in removal from the project community.
+
+## Our standards
+
+Examples of behavior that contributes to creating a positive environment include:
+
+- Using welcoming and inclusive language
+- Being respectful of differing viewpoints and experiences
+- Gracefully accepting constructive criticism
+- Focusing on what is best for the community
+- Showing empathy towards other community members
+
+Examples of unacceptable behavior by participants include:
+
+- The use of sexualized language or imagery and unwelcome sexual attention or advances
+- Trolling, insulting/derogatory comments, and personal or political attacks
+- Public or private harassment
+- Publishing others' private information, such as a physical or electronic address, without explicit permission
+- Other conduct which could reasonably be considered inappropriate in a professional setting
+
+## Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable behavior and are expected to take appropriate and fair corrective action in response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit, or reject comments, commits, code, wiki edits, issues, and other contributions that are not aligned with this Code of Conduct, or to ban temporarily or permanently any contributor for other behaviors that they deem inappropriate, threatening, offensive, or harmful.
+
+## Reporting
+
+If you are subject to or witness unacceptable behavior, or have any other concerns, please notify a project maintainer. All reports will be kept confidential and will be reviewed and investigated promptly.
+
+We will investigate every complaint and take appropriate action. We reserve the right to remove any content that violates this Code of Conduct, or to temporarily or permanently ban any contributor for other behaviors that we deem inappropriate, threatening, offensive, or harmful.
+
+## Attribution
+
+This Code of Conduct is adapted from the Contributor Covenant, version 1.4, available at <https://www.contributor-covenant.org/version/1/4/code-of-conduct.html>.

CONTRIBUTING.md

@@ -0,0 +1,49 @@
+# Contributing to Kamal development
+
+Thank you for considering contributing to Kamal! This document outlines some guidelines for contributing to this open source project.
+
+Please make sure to review our [Code of Conduct](CODE_OF_CONDUCT.md) before contributing to Kamal.
+
+There are several ways you can contribute to the betterment of the project:
+
+- **Report an issue?** - If the issue isn’t reported, we can’t fix it. Please report any bugs, feature, and/or improvement requests on the [Kamal GitHub Issues tracker](https://github.com/basecamp/kamal/issues).
+- **Submit patches** - Do you have a new feature or a fix you'd like to share? [Submit a pull request](https://github.com/basecamp/kamal/pulls)!
+- **Write blog articles** - Are you using Kamal? We'd love to hear how you're using it with your projects. Write a tutorial and post it on your blog!
+
+## Issues
+
+If you encounter any issues with the project, please check the [existing issues](https://github.com/basecamp/kamal/issues) first to see if the issue has already been reported. If the issue hasn't been reported, please open a new issue with a clear description of the problem and steps to reproduce it.
+
+## Pull Requests
+
+Please keep the following guidelines in mind when opening a pull request:
+
+- Ensure that your code passes the project's minitests by running ./bin/test.
+- Provide a clear and detailed description of your changes.
+- Keep your changes focused on a single concern.
+- Write clean and readable code that follows the project's code style.
+- Use descriptive variable and function names.
+- Write clear and concise commit messages.
+- Add tests for your changes, if possible.
+- Ensure that your changes don't break existing functionality.
+
+#### Commit message guidelines
+
+A good commit message should describe what changed and why.
+
+## Development
+
+The `main` branch is regularly built and tested, but it is not guaranteed to be completely stable. Tags are created regularly from release branches to indicate new official, stable release versions of Kamal.
+
+Kamal is written in Ruby. You should have Ruby 3.2+ installed on your machine in order to work on Kamal. If that's already setup, run `bundle` in the root directory to install all dependencies. Then you can run `bin/test` to run all tests.
+
+1. Fork the project repository.
+2. Create a new branch for your contribution.
+3. Write your code or make the desired changes.
+4. **Ensure that your code passes the project's minitests by running ./bin/test.**
+5. Commit your changes and push them to your forked repository.
+6. [Open a pull request](https://github.com/basecamp/kamal/pulls) to the main project repository with a detailed description of your changes.
+
+## License
+
+Kamal is released under the MIT License. By contributing to this project, you agree to license your contributions under the same license.

Dockerfile

@@ -0,0 +1,40 @@
+# Use the official Ruby 3.2.0 Alpine image as the base image
+FROM ruby:3.2.0-alpine
+
+# Install docker/buildx-bin
+COPY --from=docker/buildx-bin /buildx /usr/libexec/docker/cli-plugins/docker-buildx
+
+# Set the working directory to /kamal
+WORKDIR /kamal
+
+# Copy the Gemfile, Gemfile.lock into the container
+COPY Gemfile Gemfile.lock kamal.gemspec ./
+
+# Required in kamal.gemspec
+COPY lib/kamal/version.rb /kamal/lib/kamal/version.rb
+
+# Install system dependencies
+RUN apk add --no-cache build-base git docker openrc openssh-client-default \
+    && rc-update add docker boot \
+    && gem install bundler --version=2.4.3 \
+    && bundle install
+
+# Copy the rest of our application code into the container.
+# We do this after bundle install, to avoid having to run bundle
+# every time we do small fixes in the source code.
+COPY . .
+
+# Install the gem locally from the project folder
+RUN gem build kamal.gemspec && \
+    gem install ./kamal-*.gem --no-document
+
+# Set the working directory to /workdir
+WORKDIR /workdir
+
+# Tell git it's safe to access /workdir/.git even if
+# the directory is owned by a different user
+RUN git config --global --add safe.directory /workdir
+
+# Set the entrypoint to run the installed binary in /workdir
+# Example:  docker run -it -v "$PWD:/workdir" kamal init
+ENTRYPOINT ["kamal"]

Gemfile

@@ -1,8 +1,8 @@
-source 'https://rubygems.org'
+source "https://rubygems.org"
 git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
 gemspec
 
-gem "debug"
+group :rubocop do
-gem "mocha"
+  gem "rubocop-rails-omakase", require: false
-gem "railties"
+end

Gemfile.lock

@@ -1,105 +1,182 @@
 PATH
   remote: .
   specs:
-    mrsk (0.6.3)
+    kamal (1.8.1)
       activesupport (>= 7.0)
+      base64 (~> 0.2)
+      bcrypt_pbkdf (~> 1.0)
+      concurrent-ruby (~> 1.2)
       dotenv (~> 2.8)
-      sshkit (~> 1.21)
+      ed25519 (~> 1.2)
+      net-ssh (~> 7.0)
+      sshkit (>= 1.23.0, < 2.0)
       thor (~> 1.2)
       zeitwerk (~> 2.5)
 
 GEM
   remote: https://rubygems.org/
   specs:
-    actionpack (7.0.4)
+    actionpack (7.1.2)
-      actionview (= 7.0.4)
+      actionview (= 7.1.2)
-      activesupport (= 7.0.4)
+      activesupport (= 7.1.2)
-      rack (~> 2.0, >= 2.2.0)
+      nokogiri (>= 1.8.5)
+      racc
+      rack (>= 2.2.4)
+      rack-session (>= 1.0.1)
       rack-test (>= 0.6.3)
-      rails-dom-testing (~> 2.0)
+      rails-dom-testing (~> 2.2)
-      rails-html-sanitizer (~> 1.0, >= 1.2.0)
+      rails-html-sanitizer (~> 1.6)
-    actionview (7.0.4)
+    actionview (7.1.2)
-      activesupport (= 7.0.4)
+      activesupport (= 7.1.2)
       builder (~> 3.1)
-      erubi (~> 1.4)
+      erubi (~> 1.11)
-      rails-dom-testing (~> 2.0)
+      rails-dom-testing (~> 2.2)
-      rails-html-sanitizer (~> 1.1, >= 1.2.0)
+      rails-html-sanitizer (~> 1.6)
-    activesupport (7.0.4)
+    activesupport (7.1.2)
+      base64
+      bigdecimal
       concurrent-ruby (~> 1.0, >= 1.0.2)
+      connection_pool (>= 2.2.5)
+      drb
       i18n (>= 1.6, < 2)
       minitest (>= 5.1)
+      mutex_m
       tzinfo (~> 2.0)
+    ast (2.4.2)
+    base64 (0.2.0)
+    bcrypt_pbkdf (1.1.0)
+    bigdecimal (3.1.5)
     builder (3.2.4)
-    concurrent-ruby (1.1.10)
+    concurrent-ruby (1.2.2)
+    connection_pool (2.4.1)
     crass (1.0.6)
-    debug (1.7.1)
+    debug (1.9.1)
-      irb (>= 1.5.0)
+      irb (~> 1.10)
-      reline (>= 0.3.1)
+      reline (>= 0.3.8)
     dotenv (2.8.1)
+    drb (2.2.0)
+      ruby2_keywords
+    ed25519 (1.3.0)
     erubi (1.12.0)
-    i18n (1.12.0)
+    i18n (1.14.1)
       concurrent-ruby (~> 1.0)
-    io-console (0.6.0)
+    io-console (0.7.1)
-    irb (1.6.2)
+    irb (1.11.0)
-      reline (>= 0.3.0)
+      rdoc
-    loofah (2.19.1)
+      reline (>= 0.3.8)
+    json (2.7.1)
+    language_server-protocol (3.17.0.3)
+    loofah (2.22.0)
       crass (~> 1.0.2)
-      nokogiri (>= 1.5.9)
+      nokogiri (>= 1.12.0)
-    method_source (1.0.0)
+    minitest (5.20.0)
-    minitest (5.17.0)
+    mocha (2.1.0)
-    mocha (2.0.2)
       ruby2_keywords (>= 0.0.5)
+    mutex_m (0.2.0)
     net-scp (4.0.0)
       net-ssh (>= 2.6.5, < 8.0.0)
-    net-ssh (7.0.1)
+    net-sftp (4.0.0)
-    nokogiri (1.14.0-arm64-darwin)
+      net-ssh (>= 5.0.0, < 8.0.0)
+    net-ssh (7.2.1)
+    nokogiri (1.16.0-arm64-darwin)
       racc (~> 1.4)
-    nokogiri (1.14.0-x86_64-darwin)
+    nokogiri (1.16.0-x86_64-darwin)
       racc (~> 1.4)
-    nokogiri (1.14.0-x86_64-linux)
+    nokogiri (1.16.0-x86_64-linux)
       racc (~> 1.4)
-    racc (1.6.2)
+    parallel (1.24.0)
-    rack (2.2.5)
+    parser (3.3.0.5)
-    rack-test (2.0.2)
+      ast (~> 2.4.1)
+      racc
+    psych (5.1.2)
+      stringio
+    racc (1.7.3)
+    rack (3.0.8)
+    rack-session (2.0.0)
+      rack (>= 3.0.0)
+    rack-test (2.1.0)
       rack (>= 1.3)
-    rails-dom-testing (2.0.3)
+    rackup (2.1.0)
-      activesupport (>= 4.2.0)
+      rack (>= 3)
+      webrick (~> 1.8)
+    rails-dom-testing (2.2.0)
+      activesupport (>= 5.0.0)
+      minitest
       nokogiri (>= 1.6)
-    rails-html-sanitizer (1.4.4)
+    rails-html-sanitizer (1.6.0)
-      loofah (~> 2.19, >= 2.19.1)
+      loofah (~> 2.21)
-    railties (7.0.4)
+      nokogiri (~> 1.14)
-      actionpack (= 7.0.4)
+    railties (7.1.2)
-      activesupport (= 7.0.4)
+      actionpack (= 7.1.2)
-      method_source
+      activesupport (= 7.1.2)
+      irb
+      rackup (>= 1.0.0)
       rake (>= 12.2)
-      thor (~> 1.0)
+      thor (~> 1.0, >= 1.2.2)
-      zeitwerk (~> 2.5)
+      zeitwerk (~> 2.6)
-    rake (13.0.6)
+    rainbow (3.1.1)
-    reline (0.3.2)
+    rake (13.1.0)
+    rdoc (6.6.2)
+      psych (>= 4.0.0)
+    regexp_parser (2.9.0)
+    reline (0.4.2)
       io-console (~> 0.5)
+    rexml (3.2.6)
+    rubocop (1.62.1)
+      json (~> 2.3)
+      language_server-protocol (>= 3.17.0)
+      parallel (~> 1.10)
+      parser (>= 3.3.0.2)
+      rainbow (>= 2.2.2, < 4.0)
+      regexp_parser (>= 1.8, < 3.0)
+      rexml (>= 3.2.5, < 4.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
+      ruby-progressbar (~> 1.7)
+      unicode-display_width (>= 2.4.0, < 3.0)
+    rubocop-ast (1.31.2)
+      parser (>= 3.3.0.4)
+    rubocop-minitest (0.35.0)
+      rubocop (>= 1.61, < 2.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
+    rubocop-performance (1.20.2)
+      rubocop (>= 1.48.1, < 2.0)
+      rubocop-ast (>= 1.30.0, < 2.0)
+    rubocop-rails (2.24.0)
+      activesupport (>= 4.2.0)
+      rack (>= 1.1)
+      rubocop (>= 1.33.0, < 2.0)
+      rubocop-ast (>= 1.31.1, < 2.0)
+    rubocop-rails-omakase (1.0.0)
+      rubocop
+      rubocop-minitest
+      rubocop-performance
+      rubocop-rails
+    ruby-progressbar (1.13.0)
     ruby2_keywords (0.0.5)
-    sshkit (1.21.3)
+    sshkit (1.23.0)
+      base64
       net-scp (>= 1.1.2)
+      net-sftp (>= 2.1.2)
       net-ssh (>= 2.8.0)
-    thor (1.2.1)
+    stringio (3.1.0)
-    tzinfo (2.0.5)
+    thor (1.3.0)
+    tzinfo (2.0.6)
       concurrent-ruby (~> 1.0)
-    zeitwerk (2.6.6)
+    unicode-display_width (2.5.0)
+    webrick (1.8.1)
+    zeitwerk (2.6.12)
 
 PLATFORMS
-  arm64-darwin-20
+  arm64-darwin
-  arm64-darwin-21
+  x86_64-darwin
-  arm64-darwin-22
-  x86_64-darwin-20
-  x86_64-darwin-21
-  x86_64-darwin-22
   x86_64-linux
 
 DEPENDENCIES
   debug
+  kamal!
   mocha
-  mrsk!
   railties
+  rubocop-rails-omakase
 
 BUNDLED WITH
    2.4.3

README.md

@@ -1,459 +1,13 @@
-# MRSK
+# Kamal: Deploy web apps anywhere
 
-MRSK deploys web apps in containers to servers running Docker with zero downtime. It uses the dynamic reverse-proxy Traefik to hold requests while the new application container is started and the old one is stopped. It works seamlessly across multiple hosts, using SSHKit to execute commands.
+From bare metal to cloud VMs, deploy web apps anywhere with zero downtime. Kamal has the dynamic reverse-proxy Traefik hold requests while a new app container is started and the old one is stopped. Works seamlessly across multiple hosts, using SSHKit to execute commands. Originally built for Rails apps, Kamal will work with any type of web app that can be containerized with Docker.
 
-## Installation
+➡️ See [kamal-deploy.org](https://kamal-deploy.org) for documentation on [installation](https://kamal-deploy.org/docs/installation), [configuration](https://kamal-deploy.org/docs/configuration), and [commands](https://kamal-deploy.org/docs/commands).
 
-Install MRSK globally with `gem install mrsk`. Then, inside your app directory, run `mrsk init` (or `mrsk init --bundle` within Rails apps where you want a bin/mrsk binstub). Now edit the new file `config/deploy.yml`. It could look as simple as this:
+## Contributing to the documentation
 
-```yaml
+Please help us improve Kamal's documentation on the [the basecamp/kamal-site repository](https://github.com/basecamp/kamal-site).
-service: hey
-image: 37s/hey
-servers:
-  - 192.168.0.1
-  - 192.168.0.2
-registry:
-  username: registry-user-name
-  password: <%= ENV.fetch("MRSK_REGISTRY_PASSWORD") %>
-env:
-  secret:
-    - RAILS_MASTER_KEY
-```
-
-Then edit your `.env` file to add your registry password as `MRSK_REGISTRY_PASSWORD` (and your `RAILS_MASTER_KEY` for production with a Rails app).
-
-Now you're ready to deploy to the servers:
-
-```
-mrsk deploy
-```
-
-This will:
-
-1. Connect to the servers over SSH (using root by default, authenticated by your loaded ssh key)
-2. Install Docker on any server that might be missing it (using apt-get)
-3. Log into the registry both locally and remotely
-4. Build the image using the standard Dockerfile in the root of the application.
-5. Push the image to the registry.
-6. Pull the image from the registry on the servers.
-7. Ensure Traefik is running and accepting traffic on port 80.
-8. Stop any containers running a previous versions of the app.
-9. Start a new container with the version of the app that matches the current git version hash.
-10. Prune unused images and stopped containers to ensure servers don't fill up.
-
-Voila! All the servers are now serving the app on port 80. If you're just running a single server, you're ready to go. If you're running multiple servers, you need to put a load balancer in front of them.
-
-## Why not just run Capistrano, Kubernetes or Docker Swarm?
-
-MRSK basically is Capistrano for Containers, which allow us to use vanilla servers as the hosts. No need to ensure that the servers have just the right version of Ruby or other dependencies you need. That all lives in the Docker image now. You can boot a brand new Ubuntu (or whatever) server, add it to the deploy servers of MRSK, and it'll be auto-provisioned with Docker, and run right away. Docker's layer caching also allows for quicker deployments with less mucking about on the server. And the images built for MRSK can be used for CI or later introspection.
-
-Kubernetes is a beast. Running it yourself on your own hardware is not for the faint of heart. It's a fine option if you want to run on someone else's platform, either transparently [like Render](https://thenewstack.io/render-cloud-deployment-with-less-engineering/) or explicitly on AWS/GCP, but if you'd like the freedom to move between cloud and your own hardware, or even mix the two, MRSK is much simpler. You can see everything that's going on, it's just basic Docker commands being called.
-
-Docker Swarm is much simpler than Kubernetes, but it's still built on the same declarative model that uses state reconciliation. MRSK is intentionally designed to around imperative commands, like Capistrano.
-
-## Configuration
-
-### Using .env file to load required environment variables
-
-MRSK uses [dotenv](https://github.com/bkeepers/dotenv) to automatically load environment variables set in the `.env` file present in the application root. This file can be used to set variables like `MRSK_REGISTRY_PASSWORD` or database passwords. But for this reason you must ensure that .env files are not checked into Git or included in your Dockerfile! The format is just key-value like:
-
-```bash
-MRSK_REGISTRY_PASSWORD=pw
-DB_PASSWORD=secret123
-```
-
-### Using another registry than Docker Hub
-
-The default registry is Docker Hub, but you can change it using `registry/server`:
-
-```yaml
-registry:
-  server: registry.digitalocean.com
-  username: registry-user-name
-  password: <%= ENV.fetch("MRSK_REGISTRY_PASSWORD") %>
-```
-
-### Using a different SSH user than root
-
-The default SSH user is root, but you can change it using `ssh/user`:
-
-```yaml
-ssh:
-  user: app
-```
-
-### Using a proxy SSH host
-
-If you need to connect to server through a proxy host, you can use `ssh/proxy`:
-
-```yaml
-ssh:
-  proxy: "192.168.0.1" # defaults to root as the user
-```
-
-Or with specific user:
-
-```yaml
-ssh:
-  proxy: "app@192.168.0.1"
-```
-
-### Using env variables
-
-You can inject env variables into the app containers using `env`:
-
-```yaml
-env:
-  DATABASE_URL: mysql2://db1/hey_production/
-  REDIS_URL: redis://redis1:6379/1
-```
-
-### Using secret env variables
-
-If you have env variables that are secret, you can divide the `env` block into `clear` and `secret`:
-
-```yaml
-env:
-  clear:
-    DATABASE_URL: mysql2://db1/hey_production/
-    REDIS_URL: redis://redis1:6379/1
-  secret:
-    - DATABASE_PASSWORD
-    - REDIS_PASSWORD
-```
-
-The list of secret env variables will be expanded at run time from your local machine. So a reference to a secret `DATABASE_PASSWORD` will look for `ENV["DATABASE_PASSWORD"]` on the machine running MRSK. Just like with build secrets.
-
-If the referenced secret ENVs are missing, the configuration will be halted with a `KeyError` exception.
-
-Note: Marking an ENV as secret currently only redacts its value in the output for MRSK. The ENV is still injected in the clear into the container at runtime.
-
-### Using volumes
-
-You can add custom volumes into the app containers using `volumes`:
-
-```yaml
-volumes:
-  - "/local/path:/container/path"
-```
-
-### Using different roles for servers
-
-If your application uses separate hosts for running jobs or other roles beyond the default web running, you can specify these hosts in a dedicated role with a new entrypoint command like so:
-
-```yaml
-servers:
-  web:
-    - 192.168.0.1
-    - 192.168.0.2
-  job:
-    hosts:
-      - 192.168.0.3
-      - 192.168.0.4
-    cmd: bin/jobs
-```
-
-Note: Traefik will only by default be installed and run on the servers in the `web` role (and on all servers if no roles are defined). If you need Traefik on hosts in other roles than `web`, add `traefik: true`:
-
-```yaml
-servers:
-  web:
-    - 192.168.0.1
-    - 192.168.0.2
-  web2:
-    traefik: true
-    hosts:
-      - 192.168.0.3
-      - 192.168.0.4
-```
-
-### Using container labels
-
-You can specialize the default Traefik rules by setting labels on the containers that are being started:
-
-```
-labels:
-  traefik.http.routers.hey.rule: '''Host(`app.hey.com`)'''
-```
-
-Note: The extra quotes are needed to ensure the rule is passed in correctly!
-
-This allows you to run multiple applications on the same server sharing the same Traefik instance and port.
-See https://doc.traefik.io/traefik/routing/routers/#rule for a full list of available routing rules.
-
-The labels can also be applied on a per-role basis:
-
-```yaml
-servers:
-  web:
-    - 192.168.0.1
-    - 192.168.0.2
-  job:
-    hosts:
-      - 192.168.0.3
-      - 192.168.0.4
-    cmd: bin/jobs
-    labels:
-      my-label: "50"
-```
-
-### Using remote builder for native multi-arch
-
-If you're developing on ARM64 (like Apple Silicon), but you want to deploy on AMD64 (x86 64-bit), you can use multi-archecture images. By default, MRSK will setup a local buildx configuration that does this through QEMU emulation. But this can be quite slow, especially on the first build.
-
-If you want to speed up this process by using a remote AMD64 host to natively build the AMD64 part of the image, while natively building the ARM64 part locally, you can do so using builder options:
-
-```yaml
-builder:
-  local:
-    arch: arm64
-    host: unix:///Users/<%= `whoami`.strip %>/.docker/run/docker.sock
-  remote:
-    arch: amd64
-    host: ssh://root@192.168.0.1
-```
-
-Note: You must have Docker running on the remote host being used as a builder. This instance should only be shared for builds using the same registry and credentials.
-
-### Using remote builder for single-arch
-
-If you're developing on ARM64 (like Apple Silicon), want to deploy on AMD64 (x86 64-bit), but don't need to run the image locally (or on other ARM64 hosts), you can configure a remote builder that just targets AMD64. This is a bit faster than building with multi-arch, as there's nothing to build locally.
-
-```yaml
-builder:
-  remote:
-    arch: amd64
-    host: ssh://root@192.168.0.1
-```
-
-### Using native builder when multi-arch isn't needed
-
-If you're developing on the same architecture as the one you're deploying on, you can speed up the build by forgoing both multi-arch and remote building:
-
-```yaml
-builder:
-  multiarch: false
-```
-
-This is also a good option if you're running MRSK from a CI server that shares architecture with the deployment servers.
-
-### Using build secrets for new images
-
-Some images need a secret passed in during build time, like a GITHUB_TOKEN to give access to private gem repositories. This can be done by having the secret in ENV, then referencing it in the builder configuration:
-
-```yaml
-builder:
-  secrets:
-    - GITHUB_TOKEN
-```
-
-This build secret can then be referenced in the Dockerfile:
-
-```dockerfile
-# Copy Gemfiles
-COPY Gemfile Gemfile.lock ./
-
-# Install dependencies, including private repositories via access token (then remove bundle cache with exposed GITHUB_TOKEN)
-RUN --mount=type=secret,id=GITHUB_TOKEN \
-  BUNDLE_GITHUB__COM=x-access-token:$(cat /run/secrets/GITHUB_TOKEN) \
-  bundle install && \
-  rm -rf /usr/local/bundle/cache
-```
-
-### Using command arguments for Traefik
-
-You can customize the traefik command line:
-
-```yaml
-traefik:
-  args:
-    accesslog: true
-    accesslog.format: json
-```
-
-This will start the traefik container with `--accesslog=true accesslog.format=json`.
-
-### Configuring build args for new images
-
-Build arguments that aren't secret can also be configured:
-
-```yaml
-builder:
-  args:
-    RUBY_VERSION: 3.2.0
-```
-
-This build argument can then be used in the Dockerfile:
-
-```
-# Private repositories need an access token during the build
-ARG RUBY_VERSION
-FROM ruby:$RUBY_VERSION-slim as base
-```
-
-### Using accessories for database, cache, search services
-
-You can manage your accessory services via MRSK as well. The services will build off public images, and will not be automatically updated when you deploy:
-
-```yaml
-accessories:
-  mysql:
-    image: mysql:5.7
-    host: 1.1.1.3
-    port: 3306
-    env:
-      clear:
-        MYSQL_ROOT_HOST: '%'
-      secret:
-        - MYSQL_ROOT_PASSWORD
-    volumes:
-      - /var/lib/mysql:/var/lib/mysql
-  redis:
-    image: redis:latest
-    host: 1.1.1.4
-    port: "36379:6379"
-    volumes:
-      - /var/lib/redis:/data
-```
-
-Now run `mrsk accessory start mysql` to start the MySQL server on 1.1.1.3. See `mrsk accessory` for all the commands possible.
-
-### Using a generated .env file
-
-If you're using a centralized secret store, like 1Password, you can create `.env.erb` as a template which looks up the secrets. Example of a .env.erb file:
-
-```erb
-<% if (session_token = `op signin --account my-one-password-account --raw`.strip) != "" %># Generated by mrsk envify
-GITHUB_TOKEN=<%= `gh config get -h github.com oauth_token`.strip %>
-MRSK_REGISTRY_PASSWORD=<%= `op read "op://Vault/Docker Hub/password" -n --session  #{session_token}` %>
-RAILS_MASTER_KEY=<%= `op read "op://Vault/My App/RAILS_MASTER_SECRET" -n --session #{session_token}` %>
-MYSQL_ROOT_PASSWORD=<%= `op read "op://Vault/My App/MYSQL_ROOT_PASSWORD" -n --session #{session_token}` %>
-<% else raise ArgumentError, "Session token missing" end %>
-```
-
-This template can safely be checked into git. Then everyone deploying the app can run `mrsk envify` when they setup the app for the first time or passwords change to get the correct `.env` file.
-
-If you need separate env variables for different destinations, you can set them with `.env.destination.erb` for the template, which will generate `.env.staging` when run with `mrsk envify -d staging`.
-
-## Commands
-
-### Running commands on servers
-
-You can execute one-off commands on the servers:
-
-```bash
-# Runs command on all servers
-mrsk app exec 'ruby -v'
-App Host: 192.168.0.1
-ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [x86_64-linux]
-
-App Host: 192.168.0.2
-ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [x86_64-linux]
-
-# Runs command on primary server
-mrsk app exec --primary 'cat .ruby-version'
-App Host: 192.168.0.1
-3.1.3
-
-# Runs Rails command on all servers
-mrsk app exec 'bin/rails about'
-App Host: 192.168.0.1
-About your application's environment
-Rails version             7.1.0.alpha
-Ruby version              ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [x86_64-linux]
-RubyGems version          3.3.26
-Rack version              2.2.5
-Middleware                ActionDispatch::HostAuthorization, Rack::Sendfile, ActionDispatch::Static, ActionDispatch::Executor, Rack::Runtime, Rack::MethodOverride, ActionDispatch::RequestId, ActionDispatch::RemoteIp, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::DebugExceptions, ActionDispatch::Callbacks, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, ActionDispatch::ContentSecurityPolicy::Middleware, ActionDispatch::PermissionsPolicy::Middleware, Rack::Head, Rack::ConditionalGet, Rack::ETag, Rack::TempfileReaper
-Application root          /rails
-Environment               production
-Database adapter          sqlite3
-Database schema version   20221231233303
-
-App Host: 192.168.0.2
-About your application's environment
-Rails version             7.1.0.alpha
-Ruby version              ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [x86_64-linux]
-RubyGems version          3.3.26
-Rack version              2.2.5
-Middleware                ActionDispatch::HostAuthorization, Rack::Sendfile, ActionDispatch::Static, ActionDispatch::Executor, Rack::Runtime, Rack::MethodOverride, ActionDispatch::RequestId, ActionDispatch::RemoteIp, Rails::Rack::Logger, ActionDispatch::ShowExceptions, ActionDispatch::DebugExceptions, ActionDispatch::Callbacks, ActionDispatch::Cookies, ActionDispatch::Session::CookieStore, ActionDispatch::Flash, ActionDispatch::ContentSecurityPolicy::Middleware, ActionDispatch::PermissionsPolicy::Middleware, Rack::Head, Rack::ConditionalGet, Rack::ETag, Rack::TempfileReaper
-Application root          /rails
-Environment               production
-Database adapter          sqlite3
-Database schema version   20221231233303
-
-# Run Rails runner on primary server
-mrsk app exec -p 'bin/rails runner "puts Rails.application.config.time_zone"'
-UTC
-```
-
-### Running interactive commands over SSH
-
-You can run interactive commands, like a Rails console or a bash session, on a server (default is primary, use `--hosts` to connect to another):
-
-```bash
-# Starts a bash session in a new container made from the most recent app image
-mrsk app exec -i bash
-
-# Starts a bash session in the currently running container for the app
-mrsk app exec -i --reuse bash
-
-# Starts a Rails console in a new container made from the most recent app image
-mrsk app exec -i 'bin/rails console'
-```
-
-
-### Running details to see state of containers
-
-You can see the state of your servers by running `mrsk details`:
-
-```
-Traefik Host: 192.168.0.1
-CONTAINER ID   IMAGE     COMMAND                  CREATED          STATUS          PORTS                               NAMES
-6195b2a28c81   traefik   "/entrypoint.sh --pr…"   30 minutes ago   Up 19 minutes   0.0.0.0:80->80/tcp, :::80->80/tcp   traefik
-
-Traefik Host: 192.168.0.2
-CONTAINER ID   IMAGE     COMMAND                  CREATED          STATUS          PORTS                               NAMES
-de14a335d152   traefik   "/entrypoint.sh --pr…"   30 minutes ago   Up 19 minutes   0.0.0.0:80->80/tcp, :::80->80/tcp   traefik
-
-App Host: 192.168.0.1
-CONTAINER ID   IMAGE                                                                         COMMAND                  CREATED          STATUS          PORTS      NAMES
-badb1aa51db3   registry.digitalocean.com/user/app:6ef8a6a84c525b123c5245345a8483f86d05a123   "/rails/bin/docker-e…"   13 minutes ago   Up 13 minutes   3000/tcp   chat-6ef8a6a84c525b123c5245345a8483f86d05a123
-
-App Host: 192.168.0.2
-CONTAINER ID   IMAGE                                                                         COMMAND                  CREATED          STATUS          PORTS      NAMES
-1d3c91ed1f55   registry.digitalocean.com/user/app:6ef8a6a84c525b123c5245345a8483f86d05a123   "/rails/bin/docker-e…"   13 minutes ago   Up 13 minutes   3000/tcp   chat-6ef8a6a84c525b123c5245345a8483f86d05a123
-```
-
-You can also see just info for app containers with `mrsk app details` or just for Traefik with `mrsk traefik details`.
-
-### Running rollback to fix a bad deploy
-
-If you've discovered a bad deploy, you can quickly rollback by reactivating the old, paused container image. You can see what old containers are available for rollback by running `mrsk app containers`. It'll give you a presentation similar to `mrsk app details`, but include all the old containers as well. Showing something like this:
-
-```
-App Host: 192.168.0.1
-CONTAINER ID   IMAGE                                                                         COMMAND                  CREATED          STATUS                      PORTS      NAMES
-1d3c91ed1f51   registry.digitalocean.com/user/app:6ef8a6a84c525b123c5245345a8483f86d05a123   "/rails/bin/docker-e…"   19 minutes ago   Up 19 minutes               3000/tcp   chat-6ef8a6a84c525b123c5245345a8483f86d05a123
-539f26b28369   registry.digitalocean.com/user/app:e5d9d7c2b898289dfbc5f7f1334140d984eedae4   "/rails/bin/docker-e…"   31 minutes ago   Exited (1) 27 minutes ago              chat-e5d9d7c2b898289dfbc5f7f1334140d984eedae4
-
-App Host: 192.168.0.2
-CONTAINER ID   IMAGE                                                                         COMMAND                  CREATED          STATUS                      PORTS      NAMES
-badb1aa51db4   registry.digitalocean.com/user/app:6ef8a6a84c525b123c5245345a8483f86d05a123   "/rails/bin/docker-e…"   19 minutes ago   Up 19 minutes               3000/tcp   chat-6ef8a6a84c525b123c5245345a8483f86d05a123
-6f170d1172ae   registry.digitalocean.com/user/app:e5d9d7c2b898289dfbc5f7f1334140d984eedae4   "/rails/bin/docker-e…"   31 minutes ago   Exited (1) 27 minutes ago              chat-e5d9d7c2b898289dfbc5f7f1334140d984eedae4
-```
-
-From the example above, we can see that `e5d9d7c2b898289dfbc5f7f1334140d984eedae4` was the last version, so it's available as a rollback target. We can perform this rollback by running `mrsk rollback e5d9d7c2b898289dfbc5f7f1334140d984eedae4`. That'll stop `6ef8a6a84c525b123c5245345a8483f86d05a123` and then start `e5d9d7c2b898289dfbc5f7f1334140d984eedae4`. Because the old container is still available, this is very quick. Nothing to download from the registry.
-
-Note that by default old containers are pruned after 3 days when you run `mrsk deploy`.
-
-### Running removal to clean up servers
-
-If you wish to remove the entire application, including Traefik, containers, images, and registry session, you can run `mrsk remove`. This will leave the servers clean.
-
-## Stage of development
-
-This is alpha software. Lots of stuff is missing. Lots of stuff will keep moving around for a while.
 
 ## License
 
-MRSK is released under the [MIT License](https://opensource.org/licenses/MIT).
+Kamal is released under the [MIT License](https://opensource.org/licenses/MIT).

bin/docs

@@ -0,0 +1,134 @@
+#!/usr/bin/env ruby
+require "stringio"
+
+def usage
+  puts "Usage: #{$0} <kamal_site_repo>"
+  exit 1
+end
+
+usage if ARGV.size != 1
+
+kamal_site_repo = ARGV[0]
+
+if !File.directory?(kamal_site_repo)
+  puts "Error: #{kamal_site_repo} is not a directory"
+  exit 1
+end
+
+DOCS = {
+  "accessory" => "Accessories",
+  "boot" => "Booting",
+  "builder" => "Builders",
+  "configuration" => "Configuration overview",
+  "env" => "Environment variables",
+  "healthcheck" => "Healthchecks",
+  "logging" => "Logging",
+  "registry" => "Docker Registry",
+  "role" => "Roles",
+  "servers" => "Servers",
+  "ssh" => "SSH",
+  "sshkit" => "SSHKit",
+  "traefik" => "Traefik"
+}
+
+class DocWriter
+  attr_reader :from_file, :to_file, :key, :heading, :body, :output, :in_yaml
+
+  def initialize(from_file, to_dir)
+    @from_file = from_file
+    @key = File.basename(from_file, ".yml")
+    @to_file = File.join(to_dir, "#{linkify(DOCS[key])}.md")
+    @body = File.readlines(from_file)
+    @heading = body.shift.chomp("\n")
+    @output = nil
+  end
+
+  def write
+    puts "Writing #{to_file}"
+    generate_markdown
+    File.write(to_file, output.string)
+  end
+
+  private
+    def generate_markdown
+      @output = StringIO.new
+
+      generate_header
+
+      place = :in_section
+
+      loop do
+        line = body.shift&.chomp("\n")
+        break if line.nil?
+
+        case place
+        when :new_section, :in_section
+          if line.empty?
+            output.puts
+            place = :new_section
+          elsif line =~ /^ *#/
+            generate_line(line, place: place)
+            place = :in_section
+          else
+            output.puts "```yaml"
+            output.print line
+            place = :in_yaml
+          end
+        when :in_yaml
+          if line =~ /^ *#/
+            output.puts "```"
+            generate_line(line, place: :new_section)
+            place = :in_section
+          else
+            output.puts
+            output.print line
+          end
+        end
+      end
+
+      output.puts "\n```" if place == :in_yaml
+    end
+
+    def generate_header
+      output.puts "---"
+      output.puts "title: #{heading[2..-1]}"
+      output.puts "---"
+      output.puts
+      output.puts heading
+      output.puts
+    end
+
+    def generate_line(line, place: :in_section)
+      line = line.gsub(/^ *#\s?/, "")
+
+      if line =~ /(.*)kamal docs ([a-z]*)(.*)/
+        line = "#{$1}[#{DOCS[$2]}](../#{linkify(DOCS[$2])})#{$3}"
+      end
+
+      if line =~ /(.*)https:\/\/kamal-deploy.org([a-z\/-]*)(.*)/
+        line = "#{$1}[#{titlify($2.split("/").last)}](#{$2})#{$3}"
+      end
+
+      if place == :new_section
+        output.puts "## [#{line}](##{linkify(line)})"
+      else
+        output.puts line
+      end
+    end
+
+    def linkify(text)
+      text.downcase.gsub(" ", "-")
+    end
+
+    def titlify(text)
+      text.capitalize.gsub("-", " ")
+    end
+end
+
+from_dir = File.join(File.dirname(__FILE__), "../lib/kamal/configuration/docs")
+to_dir = File.join(kamal_site_repo, "docs/configuration")
+Dir.glob("#{from_dir}/*") do |from_file|
+  key = File.basename(from_file, ".yml")
+
+  DocWriter.new(from_file, to_dir).write
+end

bin/kamal

@@ -3,14 +3,16 @@
 # Prevent failures from being reported twice.
 Thread.report_on_exception = false
 
-require "mrsk"
+require "kamal"
 
 begin
-  Mrsk::Cli::Main.start(ARGV)
+  Kamal::Cli::Main.start(ARGV)
 rescue SSHKit::Runner::ExecuteError => e
-  puts "  \e[31mERROR (#{e.cause.class}): #{e.cause.message}\e[0m"
+  puts "  \e[31mERROR (#{e.cause.class}): #{e.message}\e[0m"
   puts e.cause.backtrace if ENV["VERBOSE"]
+  exit 1
 rescue => e
   puts "  \e[31mERROR (#{e.class}): #{e.message}\e[0m"
   puts e.backtrace if ENV["VERBOSE"]
+  exit 1
 end

bin/release

@@ -2,13 +2,13 @@
 
 VERSION=$1
 
-printf "module Mrsk\n  VERSION = \"$VERSION\"\nend\n" > ./lib/mrsk/version.rb
+printf "module Kamal\n  VERSION = \"$VERSION\"\nend\n" > ./lib/kamal/version.rb
 bundle
-git add Gemfile.lock lib/mrsk/version.rb
+git add Gemfile.lock lib/kamal/version.rb
 git commit -m "Bump version for $VERSION"
 git push
 git tag v$VERSION
 git push --tags
-gem build mrsk.gemspec
+gem build kamal.gemspec
-gem push "mrsk-$VERSION.gem" --host https://rubygems.org
+gem push "kamal-$VERSION.gem" --host https://rubygems.org
-rm "mrsk-$VERSION.gem"
+rm "kamal-$VERSION.gem"

gemfiles/rails_edge.gemfile

@@ -0,0 +1,9 @@
+source 'https://rubygems.org'
+git_source(:github) { |repo| "https://github.com/#{repo}.git" }
+
+git "https://github.com/rails/rails.git" do
+  gem "railties"
+  gem "activesupport"
+end
+
+gemspec path: "../"

kamal.gemspec

@@ -0,0 +1,28 @@
+require_relative "lib/kamal/version"
+
+Gem::Specification.new do |spec|
+  spec.name        = "kamal"
+  spec.version     = Kamal::VERSION
+  spec.authors     = [ "David Heinemeier Hansson" ]
+  spec.email       = "dhh@hey.com"
+  spec.homepage    = "https://github.com/basecamp/kamal"
+  spec.summary     = "Deploy web apps in containers to servers running Docker with zero downtime."
+  spec.license     = "MIT"
+  spec.files = Dir["lib/**/*", "MIT-LICENSE", "README.md"]
+  spec.executables = %w[ kamal ]
+
+  spec.add_dependency "activesupport", ">= 7.0"
+  spec.add_dependency "sshkit", ">= 1.23.0", "< 2.0"
+  spec.add_dependency "net-ssh", "~> 7.0"
+  spec.add_dependency "thor", "~> 1.2"
+  spec.add_dependency "dotenv", "~> 2.8"
+  spec.add_dependency "zeitwerk", "~> 2.5"
+  spec.add_dependency "ed25519", "~> 1.2"
+  spec.add_dependency "bcrypt_pbkdf", "~> 1.0"
+  spec.add_dependency "concurrent-ruby", "~> 1.2"
+  spec.add_dependency "base64", "~> 0.2"
+
+  spec.add_development_dependency "debug"
+  spec.add_development_dependency "mocha"
+  spec.add_development_dependency "railties"
+end

lib/kamal.rb

@@ -0,0 +1,12 @@
+module Kamal
+  class ConfigurationError < StandardError; end
+end
+
+require "active_support"
+require "zeitwerk"
+require "yaml"
+
+loader = Zeitwerk::Loader.for_gem
+loader.ignore(File.join(__dir__, "kamal", "sshkit_with_ext.rb"))
+loader.setup
+loader.eager_load # We need all commands loaded.

lib/kamal/cli.rb

@@ -0,0 +1,7 @@
+module Kamal::Cli
+  class HookError < StandardError; end
+  class LockError < StandardError; end
+end
+
+# SSHKit uses instance eval, so we need a global const for ergonomics
+KAMAL = Kamal::Commander.new

lib/kamal/cli/accessory.rb

@@ -0,0 +1,259 @@
+class Kamal::Cli::Accessory < Kamal::Cli::Base
+  desc "boot [NAME]", "Boot new accessory service on host (use NAME=all to boot all accessories)"
+  def boot(name, login: true)
+    with_lock do
+      if name == "all"
+        KAMAL.accessory_names.each { |accessory_name| boot(accessory_name) }
+      else
+        with_accessory(name) do |accessory, hosts|
+          directories(name)
+          upload(name)
+
+          on(hosts) do
+            execute *KAMAL.registry.login if login
+            execute *KAMAL.auditor.record("Booted #{name} accessory"), verbosity: :debug
+            execute *accessory.run
+          end
+        end
+      end
+    end
+  end
+
+  desc "upload [NAME]", "Upload accessory files to host", hide: true
+  def upload(name)
+    with_lock do
+      with_accessory(name) do |accessory, hosts|
+        on(hosts) do
+          accessory.files.each do |(local, remote)|
+            accessory.ensure_local_file_present(local)
+
+            execute *accessory.make_directory_for(remote)
+            upload! local, remote
+            execute :chmod, "755", remote
+          end
+        end
+      end
+    end
+  end
+
+  desc "directories [NAME]", "Create accessory directories on host", hide: true
+  def directories(name)
+    with_lock do
+      with_accessory(name) do |accessory, hosts|
+        on(hosts) do
+          accessory.directories.keys.each do |host_path|
+            execute *accessory.make_directory(host_path)
+          end
+        end
+      end
+    end
+  end
+
+  desc "reboot [NAME]", "Reboot existing accessory on host (stop container, remove container, start new container; use NAME=all to boot all accessories)"
+  def reboot(name)
+    with_lock do
+      if name == "all"
+        KAMAL.accessory_names.each { |accessory_name| reboot(accessory_name) }
+      else
+        with_accessory(name) do |accessory, hosts|
+          on(hosts) do
+            execute *KAMAL.registry.login
+          end
+
+          stop(name)
+          remove_container(name)
+          boot(name, login: false)
+        end
+      end
+    end
+  end
+
+  desc "start [NAME]", "Start existing accessory container on host"
+  def start(name)
+    with_lock do
+      with_accessory(name) do |accessory, hosts|
+        on(hosts) do
+          execute *KAMAL.auditor.record("Started #{name} accessory"), verbosity: :debug
+          execute *accessory.start
+        end
+      end
+    end
+  end
+
+  desc "stop [NAME]", "Stop existing accessory container on host"
+  def stop(name)
+    with_lock do
+      with_accessory(name) do |accessory, hosts|
+        on(hosts) do
+          execute *KAMAL.auditor.record("Stopped #{name} accessory"), verbosity: :debug
+          execute *accessory.stop, raise_on_non_zero_exit: false
+        end
+      end
+    end
+  end
+
+  desc "restart [NAME]", "Restart existing accessory container on host"
+  def restart(name)
+    with_lock do
+      with_accessory(name) do
+        stop(name)
+        start(name)
+      end
+    end
+  end
+
+  desc "details [NAME]", "Show details about accessory on host (use NAME=all to show all accessories)"
+  def details(name)
+    if name == "all"
+      KAMAL.accessory_names.each { |accessory_name| details(accessory_name) }
+    else
+      type = "Accessory #{name}"
+      with_accessory(name) do |accessory, hosts|
+        on(hosts) { puts_by_host host, capture_with_info(*accessory.info), type: type }
+      end
+    end
+  end
+
+  desc "exec [NAME] [CMD]", "Execute a custom command on servers (use --help to show options)"
+  option :interactive, aliases: "-i", type: :boolean, default: false, desc: "Execute command over ssh for an interactive shell (use for console/bash)"
+  option :reuse, type: :boolean, default: false, desc: "Reuse currently running container instead of starting a new one"
+  def exec(name, cmd)
+    with_accessory(name) do |accessory, hosts|
+      case
+      when options[:interactive] && options[:reuse]
+        say "Launching interactive command with via SSH from existing container...", :magenta
+        run_locally { exec accessory.execute_in_existing_container_over_ssh(cmd) }
+
+      when options[:interactive]
+        say "Launching interactive command via SSH from new container...", :magenta
+        run_locally { exec accessory.execute_in_new_container_over_ssh(cmd) }
+
+      when options[:reuse]
+        say "Launching command from existing container...", :magenta
+        on(hosts) do
+          execute *KAMAL.auditor.record("Executed cmd '#{cmd}' on #{name} accessory"), verbosity: :debug
+          capture_with_info(*accessory.execute_in_existing_container(cmd))
+        end
+
+      else
+        say "Launching command from new container...", :magenta
+        on(hosts) do
+          execute *KAMAL.auditor.record("Executed cmd '#{cmd}' on #{name} accessory"), verbosity: :debug
+          capture_with_info(*accessory.execute_in_new_container(cmd))
+        end
+      end
+    end
+  end
+
+  desc "logs [NAME]", "Show log lines from accessory on host (use --help to show options)"
+  option :since, aliases: "-s", desc: "Show logs since timestamp (e.g. 2013-01-02T13:23:37Z) or relative (e.g. 42m for 42 minutes)"
+  option :lines, type: :numeric, aliases: "-n", desc: "Number of log lines to pull from each server"
+  option :grep, aliases: "-g", desc: "Show lines with grep match only (use this to fetch specific requests by id)"
+  option :grep_options, aliases: "-o", desc: "Additional options supplied to grep"
+  option :follow, aliases: "-f", desc: "Follow logs on primary server (or specific host set by --hosts)"
+  def logs(name)
+    with_accessory(name) do |accessory, hosts|
+      grep = options[:grep]
+      grep_options = options[:grep_options]
+
+      if options[:follow]
+        run_locally do
+          info "Following logs on #{hosts}..."
+          info accessory.follow_logs(grep: grep, grep_options: grep_options)
+          exec accessory.follow_logs(grep: grep, grep_options: grep_options)
+        end
+      else
+        since = options[:since]
+        lines = options[:lines].presence || ((since || grep) ? nil : 100) # Default to 100 lines if since or grep isn't set
+
+        on(hosts) do
+          puts capture_with_info(*accessory.logs(since: since, lines: lines, grep: grep, grep_options: grep_options))
+        end
+      end
+    end
+  end
+
+  desc "remove [NAME]", "Remove accessory container, image and data directory from host (use NAME=all to remove all accessories)"
+  option :confirmed, aliases: "-y", type: :boolean, default: false, desc: "Proceed without confirmation question"
+  def remove(name)
+    confirming "This will remove all containers, images and data directories for #{name}. Are you sure?" do
+      with_lock do
+        if name == "all"
+          KAMAL.accessory_names.each { |accessory_name| remove_accessory(accessory_name) }
+        else
+          remove_accessory(name)
+        end
+      end
+    end
+  end
+
+  desc "remove_container [NAME]", "Remove accessory container from host", hide: true
+  def remove_container(name)
+    with_lock do
+      with_accessory(name) do |accessory, hosts|
+        on(hosts) do
+          execute *KAMAL.auditor.record("Remove #{name} accessory container"), verbosity: :debug
+          execute *accessory.remove_container
+        end
+      end
+    end
+  end
+
+  desc "remove_image [NAME]", "Remove accessory image from host", hide: true
+  def remove_image(name)
+    with_lock do
+      with_accessory(name) do |accessory, hosts|
+        on(hosts) do
+          execute *KAMAL.auditor.record("Removed #{name} accessory image"), verbosity: :debug
+          execute *accessory.remove_image
+        end
+      end
+    end
+  end
+
+  desc "remove_service_directory [NAME]", "Remove accessory directory used for uploaded files and data directories from host", hide: true
+  def remove_service_directory(name)
+    with_lock do
+      with_accessory(name) do |accessory, hosts|
+        on(hosts) do
+          execute *accessory.remove_service_directory
+        end
+      end
+    end
+  end
+
+  private
+    def with_accessory(name)
+      if KAMAL.config.accessory(name)
+        accessory = KAMAL.accessory(name)
+        yield accessory, accessory_hosts(accessory)
+      else
+        error_on_missing_accessory(name)
+      end
+    end
+
+    def error_on_missing_accessory(name)
+      options = KAMAL.accessory_names.presence
+
+      error \
+        "No accessory by the name of '#{name}'" +
+        (options ? " (options: #{options.to_sentence})" : "")
+    end
+
+    def accessory_hosts(accessory)
+      if KAMAL.specific_hosts&.any?
+        KAMAL.specific_hosts & accessory.hosts
+      else
+        accessory.hosts
+      end
+    end
+
+    def remove_accessory(name)
+      with_accessory(name) do
+        stop(name)
+        remove_container(name)
+        remove_image(name)
+        remove_service_directory(name)
+      end
+    end
+end

lib/kamal/cli/app.rb

@@ -0,0 +1,298 @@
+class Kamal::Cli::App < Kamal::Cli::Base
+  desc "boot", "Boot app on servers (or reboot app if already running)"
+  def boot
+    with_lock do
+      say "Get most recent version available as an image...", :magenta unless options[:version]
+      using_version(version_or_latest) do |version|
+        say "Start container with version #{version} using a #{KAMAL.config.readiness_delay}s readiness delay (or reboot if already running)...", :magenta
+
+        # Assets are prepared in a separate step to ensure they are on all hosts before booting
+        on(KAMAL.hosts) do
+          KAMAL.roles_on(host).each do |role|
+            Kamal::Cli::App::PrepareAssets.new(host, role, self).run
+          end
+        end
+
+        # Primary hosts and roles are returned first, so they can open the barrier
+        barrier = Kamal::Cli::Healthcheck::Barrier.new
+
+        on(KAMAL.hosts, **KAMAL.boot_strategy) do |host|
+          KAMAL.roles_on(host).each do |role|
+            Kamal::Cli::App::Boot.new(host, role, self, version, barrier).run
+          end
+        end
+
+        # Tag once the app booted on all hosts
+        on(KAMAL.hosts) do |host|
+          execute *KAMAL.auditor.record("Tagging #{KAMAL.config.absolute_image} as the latest image"), verbosity: :debug
+          execute *KAMAL.app.tag_latest_image
+        end
+      end
+    end
+  end
+
+  desc "start", "Start existing app container on servers"
+  def start
+    with_lock do
+      on(KAMAL.hosts) do |host|
+        roles = KAMAL.roles_on(host)
+
+        roles.each do |role|
+          execute *KAMAL.auditor.record("Started app version #{KAMAL.config.version}"), verbosity: :debug
+          execute *KAMAL.app(role: role, host: host).start, raise_on_non_zero_exit: false
+        end
+      end
+    end
+  end
+
+  desc "stop", "Stop app container on servers"
+  def stop
+    with_lock do
+      on(KAMAL.hosts) do |host|
+        roles = KAMAL.roles_on(host)
+
+        roles.each do |role|
+          execute *KAMAL.auditor.record("Stopped app", role: role), verbosity: :debug
+          execute *KAMAL.app(role: role, host: host).stop, raise_on_non_zero_exit: false
+        end
+      end
+    end
+  end
+
+  # FIXME: Drop in favor of just containers?
+  desc "details", "Show details about app containers"
+  def details
+    on(KAMAL.hosts) do |host|
+      roles = KAMAL.roles_on(host)
+
+      roles.each do |role|
+        puts_by_host host, capture_with_info(*KAMAL.app(role: role, host: host).info)
+      end
+    end
+  end
+
+  desc "exec [CMD]", "Execute a custom command on servers within the app container (use --help to show options)"
+  option :interactive, aliases: "-i", type: :boolean, default: false, desc: "Execute command over ssh for an interactive shell (use for console/bash)"
+  option :reuse, type: :boolean, default: false, desc: "Reuse currently running container instead of starting a new one"
+  option :env, aliases: "-e", type: :hash, desc: "Set environment variables for the command"
+  def exec(cmd)
+    env = options[:env]
+    case
+    when options[:interactive] && options[:reuse]
+      say "Get current version of running container...", :magenta unless options[:version]
+      using_version(options[:version] || current_running_version) do |version|
+        say "Launching interactive command with version #{version} via SSH from existing container on #{KAMAL.primary_host}...", :magenta
+        run_locally { exec KAMAL.app(role: KAMAL.primary_role, host: KAMAL.primary_host).execute_in_existing_container_over_ssh(cmd, env: env) }
+      end
+
+    when options[:interactive]
+      say "Get most recent version available as an image...", :magenta unless options[:version]
+      using_version(version_or_latest) do |version|
+        say "Launching interactive command with version #{version} via SSH from new container on #{KAMAL.primary_host}...", :magenta
+        run_locally do
+          exec KAMAL.app(role: KAMAL.primary_role, host: KAMAL.primary_host).execute_in_new_container_over_ssh(cmd, env: env)
+        end
+      end
+
+    when options[:reuse]
+      say "Get current version of running container...", :magenta unless options[:version]
+      using_version(options[:version] || current_running_version) do |version|
+        say "Launching command with version #{version} from existing container...", :magenta
+
+        on(KAMAL.hosts) do |host|
+          roles = KAMAL.roles_on(host)
+
+          roles.each do |role|
+            execute *KAMAL.auditor.record("Executed cmd '#{cmd}' on app version #{version}", role: role), verbosity: :debug
+            puts_by_host host, capture_with_info(*KAMAL.app(role: role, host: host).execute_in_existing_container(cmd, env: env))
+          end
+        end
+      end
+
+    else
+      say "Get most recent version available as an image...", :magenta unless options[:version]
+      using_version(version_or_latest) do |version|
+        say "Launching command with version #{version} from new container...", :magenta
+        on(KAMAL.hosts) do |host|
+          roles = KAMAL.roles_on(host)
+
+          roles.each do |role|
+            execute *KAMAL.auditor.record("Executed cmd '#{cmd}' on app version #{version}"), verbosity: :debug
+            puts_by_host host, capture_with_info(*KAMAL.app(role: role, host: host).execute_in_new_container(cmd, env: env))
+          end
+        end
+      end
+    end
+  end
+
+  desc "containers", "Show app containers on servers"
+  def containers
+    on(KAMAL.hosts) { |host| puts_by_host host, capture_with_info(*KAMAL.app.list_containers) }
+  end
+
+  desc "stale_containers", "Detect app stale containers"
+  option :stop, aliases: "-s", type: :boolean, default: false, desc: "Stop the stale containers found"
+  def stale_containers
+    stop = options[:stop]
+
+    with_lock_if_stopping do
+      on(KAMAL.hosts) do |host|
+        roles = KAMAL.roles_on(host)
+
+        roles.each do |role|
+          app = KAMAL.app(role: role, host: host)
+          versions = capture_with_info(*app.list_versions, raise_on_non_zero_exit: false).split("\n")
+          versions -= [ capture_with_info(*app.current_running_version, raise_on_non_zero_exit: false).strip ]
+
+          versions.each do |version|
+            if stop
+              puts_by_host host, "Stopping stale container for role #{role} with version #{version}"
+              execute *app.stop(version: version), raise_on_non_zero_exit: false
+            else
+              puts_by_host host,  "Detected stale container for role #{role} with version #{version} (use `kamal app stale_containers --stop` to stop)"
+            end
+          end
+        end
+      end
+    end
+  end
+
+  desc "images", "Show app images on servers"
+  def images
+    on(KAMAL.hosts) { |host| puts_by_host host, capture_with_info(*KAMAL.app.list_images) }
+  end
+
+  desc "logs", "Show log lines from app on servers (use --help to show options)"
+  option :since, aliases: "-s", desc: "Show lines since timestamp (e.g. 2013-01-02T13:23:37Z) or relative (e.g. 42m for 42 minutes)"
+  option :lines, type: :numeric, aliases: "-n", desc: "Number of lines to show from each server"
+  option :grep, aliases: "-g", desc: "Show lines with grep match only (use this to fetch specific requests by id)"
+  option :grep_options, aliases: "-o", desc: "Additional options supplied to grep"
+  option :follow, aliases: "-f", desc: "Follow log on primary server (or specific host set by --hosts)"
+  def logs
+    # FIXME: Catch when app containers aren't running
+
+    grep = options[:grep]
+    grep_options = options[:grep_options]
+    since = options[:since]
+
+    if options[:follow]
+      lines = options[:lines].presence || ((since || grep) ? nil : 10) # Default to 10 lines if since or grep isn't set
+
+      run_locally do
+        info "Following logs on #{KAMAL.primary_host}..."
+
+        KAMAL.specific_roles ||= [ "web" ]
+        role = KAMAL.roles_on(KAMAL.primary_host).first
+
+        app = KAMAL.app(role: role, host: host)
+        info app.follow_logs(host: KAMAL.primary_host, lines: lines, grep: grep, grep_options: grep_options)
+        exec app.follow_logs(host: KAMAL.primary_host, lines: lines, grep: grep, grep_options: grep_options)
+      end
+    else
+      lines = options[:lines].presence || ((since || grep) ? nil : 100) # Default to 100 lines if since or grep isn't set
+
+      on(KAMAL.hosts) do |host|
+        roles = KAMAL.roles_on(host)
+
+        roles.each do |role|
+          begin
+            puts_by_host host, capture_with_info(*KAMAL.app(role: role, host: host).logs(since: since, lines: lines, grep: grep, grep_options: grep_options))
+          rescue SSHKit::Command::Failed
+            puts_by_host host, "Nothing found"
+          end
+        end
+      end
+    end
+  end
+
+  desc "remove", "Remove app containers and images from servers"
+  def remove
+    with_lock do
+      stop
+      remove_containers
+      remove_images
+    end
+  end
+
+  desc "remove_container [VERSION]", "Remove app container with given version from servers", hide: true
+  def remove_container(version)
+    with_lock do
+      on(KAMAL.hosts) do |host|
+        roles = KAMAL.roles_on(host)
+
+        roles.each do |role|
+          execute *KAMAL.auditor.record("Removed app container with version #{version}", role: role), verbosity: :debug
+          execute *KAMAL.app(role: role, host: host).remove_container(version: version)
+        end
+      end
+    end
+  end
+
+  desc "remove_containers", "Remove all app containers from servers", hide: true
+  def remove_containers
+    with_lock do
+      on(KAMAL.hosts) do |host|
+        roles = KAMAL.roles_on(host)
+
+        roles.each do |role|
+          execute *KAMAL.auditor.record("Removed all app containers", role: role), verbosity: :debug
+          execute *KAMAL.app(role: role, host: host).remove_containers
+        end
+      end
+    end
+  end
+
+  desc "remove_images", "Remove all app images from servers", hide: true
+  def remove_images
+    with_lock do
+      on(KAMAL.hosts) do
+        execute *KAMAL.auditor.record("Removed all app images"), verbosity: :debug
+        execute *KAMAL.app.remove_images
+      end
+    end
+  end
+
+  desc "version", "Show app version currently running on servers"
+  def version
+    on(KAMAL.hosts) do |host|
+      role = KAMAL.roles_on(host).first
+      puts_by_host host, capture_with_info(*KAMAL.app(role: role, host: host).current_running_version).strip
+    end
+  end
+
+  private
+    def using_version(new_version)
+      if new_version
+        begin
+          old_version = KAMAL.config.version
+          KAMAL.config.version = new_version
+          yield new_version
+        ensure
+          KAMAL.config.version = old_version
+        end
+      else
+        yield KAMAL.config.version
+      end
+    end
+
+    def current_running_version(host: KAMAL.primary_host)
+      version = nil
+      on(host) do
+        role = KAMAL.roles_on(host).first
+        version = capture_with_info(*KAMAL.app(role: role, host: host).current_running_version).strip
+      end
+      version.presence
+    end
+
+    def version_or_latest
+      options[:version] || KAMAL.config.latest_tag
+    end
+
+    def with_lock_if_stopping
+      if options[:stop]
+        with_lock { yield }
+      else
+        yield
+      end
+    end
+end

lib/kamal/cli/app/boot.rb

@@ -0,0 +1,119 @@
+class Kamal::Cli::App::Boot
+  attr_reader :host, :role, :version, :barrier, :sshkit
+  delegate :execute, :capture_with_info, :capture_with_pretty_json, :info, :error, to: :sshkit
+  delegate :uses_cord?, :assets?, :running_traefik?, to: :role
+
+  def initialize(host, role, sshkit, version, barrier)
+    @host = host
+    @role = role
+    @version = version
+    @barrier = barrier
+    @sshkit = sshkit
+  end
+
+  def run
+    old_version = old_version_renamed_if_clashing
+
+    wait_at_barrier if queuer?
+
+    begin
+      start_new_version
+    rescue => e
+      close_barrier if gatekeeper?
+      stop_new_version
+      raise
+    end
+
+    release_barrier if gatekeeper?
+
+    if old_version
+      stop_old_version(old_version)
+    end
+  end
+
+  private
+    def old_version_renamed_if_clashing
+      if capture_with_info(*app.container_id_for_version(version), raise_on_non_zero_exit: false).present?
+        renamed_version = "#{version}_replaced_#{SecureRandom.hex(8)}"
+        info "Renaming container #{version} to #{renamed_version} as already deployed on #{host}"
+        audit("Renaming container #{version} to #{renamed_version}")
+        execute *app.rename_container(version: version, new_version: renamed_version)
+      end
+
+      capture_with_info(*app.current_running_version, raise_on_non_zero_exit: false).strip.presence
+    end
+
+    def start_new_version
+      audit "Booted app version #{version}"
+
+      execute *app.tie_cord(role.cord_host_file) if uses_cord?
+      hostname = "#{host.to_s[0...51].gsub(/\.+$/, '')}-#{SecureRandom.hex(6)}"
+      execute *app.run(hostname: hostname)
+      Kamal::Cli::Healthcheck::Poller.wait_for_healthy(pause_after_ready: true) { capture_with_info(*app.status(version: version)) }
+    end
+
+    def stop_new_version
+      execute *app.stop(version: version), raise_on_non_zero_exit: false
+    end
+
+    def stop_old_version(version)
+      if uses_cord?
+        cord = capture_with_info(*app.cord(version: version), raise_on_non_zero_exit: false).strip
+        if cord.present?
+          execute *app.cut_cord(cord)
+          Kamal::Cli::Healthcheck::Poller.wait_for_unhealthy(pause_after_ready: true) { capture_with_info(*app.status(version: version)) }
+        end
+      end
+
+      execute *app.stop(version: version), raise_on_non_zero_exit: false
+
+      execute *app.clean_up_assets if assets?
+    end
+
+    def release_barrier
+      if barrier.open
+        info "First #{KAMAL.primary_role} container is healthy on #{host}, booting any other roles"
+      end
+    end
+
+    def wait_at_barrier
+      info "Waiting for the first healthy #{KAMAL.primary_role} container before booting #{role} on #{host}..."
+      barrier.wait
+      info "First #{KAMAL.primary_role} container is healthy, booting #{role} on #{host}..."
+    rescue Kamal::Cli::Healthcheck::Error
+      info "First #{KAMAL.primary_role} container is unhealthy, not booting #{role} on #{host}"
+      raise
+    end
+
+    def close_barrier
+      if barrier.close
+        info "First #{KAMAL.primary_role} container is unhealthy on #{host}, not booting any other roles"
+        error capture_with_info(*app.logs(version: version))
+        error capture_with_info(*app.container_health_log(version: version))
+      end
+    end
+
+    def barrier_role?
+      role == KAMAL.primary_role
+    end
+
+    def app
+      @app ||= KAMAL.app(role: role, host: host)
+    end
+
+    def auditor
+      @auditor = KAMAL.auditor(role: role)
+    end
+
+    def audit(message)
+      execute *auditor.record(message), verbosity: :debug
+    end
+
+    def gatekeeper?
+      barrier && barrier_role?
+    end
+
+    def queuer?
+      barrier && !barrier_role?
+    end
+end

lib/kamal/cli/app/prepare_assets.rb

@@ -0,0 +1,24 @@
+class Kamal::Cli::App::PrepareAssets
+  attr_reader :host, :role, :sshkit
+  delegate :execute, :capture_with_info, :info, to: :sshkit
+  delegate :assets?, to: :role
+
+  def initialize(host, role, sshkit)
+    @host = host
+    @role = role
+    @sshkit = sshkit
+  end
+
+  def run
+    if assets?
+      execute *app.extract_assets
+      old_version = capture_with_info(*app.current_running_version, raise_on_non_zero_exit: false).strip
+      execute *app.sync_asset_volumes(old_version: old_version)
+    end
+  end
+
+  private
+    def app
+      @app ||= KAMAL.app(role: role, host: host)
+    end
+end

lib/kamal/cli/base.rb

@@ -0,0 +1,236 @@
+require "thor"
+require "dotenv"
+require "kamal/sshkit_with_ext"
+
+module Kamal::Cli
+  class Base < Thor
+    include SSHKit::DSL
+
+    def self.exit_on_failure?() true end
+
+    class_option :verbose, type: :boolean, aliases: "-v", desc: "Detailed logging"
+    class_option :quiet, type: :boolean, aliases: "-q", desc: "Minimal logging"
+
+    class_option :version, desc: "Run commands against a specific app version"
+
+    class_option :primary, type: :boolean, aliases: "-p", desc: "Run commands only on primary host instead of all"
+    class_option :hosts, aliases: "-h", desc: "Run commands on these hosts instead of all (separate by comma, supports wildcards with *)"
+    class_option :roles, aliases: "-r", desc: "Run commands on these roles instead of all (separate by comma, supports wildcards with *)"
+
+    class_option :config_file, aliases: "-c", default: "config/deploy.yml", desc: "Path to config file"
+    class_option :destination, aliases: "-d", desc: "Specify destination to be used for config file (staging -> deploy.staging.yml)"
+
+    class_option :skip_hooks, aliases: "-H", type: :boolean, default: false, desc: "Don't run hooks"
+
+    @@ran_pre_init_hook = false
+    class << self
+      def ran_pre_init_hook
+        @@ran_pre_init_hook
+      end
+
+      def ran_pre_init_hook=(value)
+        @@ran_pre_init_hook = value
+      end
+    end
+
+    def initialize(*)
+      super
+      @original_env = ENV.to_h.dup
+      run_pre_init_hook
+      load_env
+      initialize_commander(options_with_subcommand_class_options)
+    end
+
+    private
+      def load_env
+        if destination = options[:destination]
+          if File.exist?(".kamal/.env.#{destination}") || File.exist?(".kamal/.env")
+            Dotenv.load(".kamal/.env.#{destination}", ".kamal/.env")
+          else
+            loading_files = [ (".env" if File.exist?(".env")), (".env.#{destination}" if File.exist?(".env.#{destination}")) ].compact
+            if loading_files.any?
+              warn "Loading #{loading_files.join(" and ")} from the project root, in future they will be loaded from .kamal/"
+              Dotenv.load(".env.#{destination}", ".env")
+            end
+          end
+        else
+          if File.exist?(".kamal/.env")
+            Dotenv.load(".kamal/.env")
+          elsif File.exist?(".env")
+            $stderr.puts caller
+            warn "Loading .env from the project root, in future it will be loaded then from .kamal/.env"
+            Dotenv.load(".env")
+          end
+        end
+      end
+
+      def options_with_subcommand_class_options
+        options.merge(@_initializer.last[:class_options] || {})
+      end
+
+      def initialize_commander(options)
+        KAMAL.tap do |commander|
+          if options[:verbose]
+            ENV["VERBOSE"] = "1" # For backtraces via cli/start
+            commander.verbosity = :debug
+          end
+
+          if options[:quiet]
+            commander.verbosity = :error
+          end
+
+          commander.configure \
+            config_file: Pathname.new(File.expand_path(options[:config_file])),
+            destination: options[:destination],
+            version: options[:version]
+
+          commander.specific_hosts    = options[:hosts]&.split(",")
+          commander.specific_roles    = options[:roles]&.split(",")
+          commander.specific_primary! if options[:primary]
+        end
+      end
+
+      def print_runtime
+        started_at = Time.now
+        yield
+        Time.now - started_at
+      ensure
+        runtime = Time.now - started_at
+        puts "  Finished all in #{sprintf("%.1f seconds", runtime)}"
+      end
+
+      def with_lock
+        if KAMAL.holding_lock?
+          yield
+        else
+          ensure_run_and_locks_directory
+
+          acquire_lock
+
+          begin
+            yield
+          rescue
+            begin
+              release_lock
+            rescue => e
+              say "Error releasing the deploy lock: #{e.message}", :red
+            end
+            raise
+          end
+
+          release_lock
+        end
+      end
+
+      def confirming(question)
+        return yield if options[:confirmed]
+
+        if ask(question, limited_to: %w[ y N ], default: "N") == "y"
+          yield
+        else
+          say "Aborted", :red
+        end
+      end
+
+      def acquire_lock
+        raise_if_locked do
+          say "Acquiring the deploy lock...", :magenta
+          on(KAMAL.primary_host) { execute *KAMAL.lock.acquire("Automatic deploy lock", KAMAL.config.version), verbosity: :debug }
+        end
+
+        KAMAL.holding_lock = true
+      end
+
+      def release_lock
+        say "Releasing the deploy lock...", :magenta
+        on(KAMAL.primary_host) { execute *KAMAL.lock.release, verbosity: :debug }
+
+        KAMAL.holding_lock = false
+      end
+
+      def raise_if_locked
+        yield
+      rescue SSHKit::Runner::ExecuteError => e
+        if e.message =~ /cannot create directory/
+          say "Deploy lock already in place!", :red
+          on(KAMAL.primary_host) { puts capture_with_debug(*KAMAL.lock.status) }
+          raise LockError, "Deploy lock found. Run 'kamal lock help' for more information"
+        else
+          raise e
+        end
+      end
+
+      def run_pre_init_hook
+        unless self.class.ran_pre_init_hook
+          hook = "pre-init"
+          if run_hook?(hook)
+            say "Running the #{hook} hook...", :magenta
+            run_locally do
+              execute *Kamal::Hooks.file(hook), verbosity: :debug
+            rescue SSHKit::Command::Failed => e
+              raise HookError.new("Hook `#{hook}` failed:\n#{e.message}")
+            end
+          end
+          self.class.ran_pre_init_hook = true
+        end
+      end
+
+      def run_hook(hook, **extra_details)
+        if run_hook?(hook)
+          details = { hosts: KAMAL.hosts.join(","), command: command, subcommand: subcommand }
+
+          say "Running the #{hook} hook...", :magenta
+          run_locally do
+            execute *KAMAL.hook.run(hook, **details, **extra_details)
+          rescue SSHKit::Command::Failed => e
+            raise HookError.new("Hook `#{hook}` failed:\n#{e.message}")
+          end
+        end
+      end
+
+      def run_hook?(hook)
+        !options[:skip_hooks] && Kamal::Hooks.exists?(hook)
+      end
+
+      def on(*args, &block)
+        if !KAMAL.connected?
+          run_hook "pre-connect"
+          KAMAL.connected = true
+        end
+
+        super
+      end
+
+      def command
+        @kamal_command ||= begin
+          invocation_class, invocation_commands = *first_invocation
+          if invocation_class == Kamal::Cli::Main
+            invocation_commands[0]
+          else
+            Kamal::Cli::Main.subcommand_classes.find { |command, clazz| clazz == invocation_class }[0]
+          end
+        end
+      end
+
+      def subcommand
+        @kamal_subcommand ||= begin
+          invocation_class, invocation_commands = *first_invocation
+          invocation_commands[0] if invocation_class != Kamal::Cli::Main
+        end
+      end
+
+      def first_invocation
+        instance_variable_get("@_invocations").first
+      end
+
+      def ensure_run_and_locks_directory
+        on(KAMAL.hosts) do
+          execute(*KAMAL.server.ensure_run_directory)
+        end
+
+        on(KAMAL.primary_host) do
+          execute(*KAMAL.lock.ensure_locks_directory)
+        end
+      end
+  end
+end

lib/kamal/cli/build.rb

@@ -0,0 +1,161 @@
+require "uri"
+
+class Kamal::Cli::Build < Kamal::Cli::Base
+  class BuildError < StandardError; end
+
+  desc "deliver", "Build app and push app image to registry then pull image on servers"
+  def deliver
+    push
+    pull
+  end
+
+  desc "push", "Build and push app image to registry"
+  def push
+    cli = self
+
+    verify_local_dependencies
+    run_hook "pre-build"
+
+    uncommitted_changes = Kamal::Git.uncommitted_changes
+
+    if KAMAL.config.builder.git_clone?
+      if uncommitted_changes.present?
+        say "Building from a local git clone, so ignoring these uncommitted changes:\n #{uncommitted_changes}", :yellow
+      end
+
+      run_locally do
+        Clone.new(self).prepare
+      end
+    elsif uncommitted_changes.present?
+      say "Building with uncommitted changes:\n #{uncommitted_changes}", :yellow
+    end
+
+    # Get the command here to ensure the Dir.chdir doesn't interfere with it
+    push = KAMAL.builder.push
+
+    run_locally do
+      begin
+        context_hosts = capture_with_info(*KAMAL.builder.context_hosts).split("\n")
+
+        if context_hosts != KAMAL.builder.config_context_hosts
+          warn "Context hosts have changed, so re-creating builder, was: #{context_hosts.join(", ")}], now: #{KAMAL.builder.config_context_hosts.join(", ")}"
+          cli.remove
+          cli.create
+        end
+      rescue SSHKit::Command::Failed => e
+        if e.message =~ /(context not found|no builder|does not exist)/
+          warn "Missing compatible builder, so creating a new one first"
+          cli.create
+        else
+          raise
+        end
+      end
+
+      KAMAL.with_verbosity(:debug) do
+        Dir.chdir(KAMAL.config.builder.build_directory) { execute *push }
+      end
+    end
+  end
+
+  desc "pull", "Pull app image from registry onto servers"
+  def pull
+    if (first_hosts = mirror_hosts).any?
+      #  Pull on a single host per mirror first to seed them
+      say "Pulling image on #{first_hosts.join(", ")} to seed the #{"mirror".pluralize(first_hosts.count)}...", :magenta
+      pull_on_hosts(first_hosts)
+      say "Pulling image on remaining hosts...", :magenta
+      pull_on_hosts(KAMAL.hosts - first_hosts)
+    else
+      pull_on_hosts(KAMAL.hosts)
+    end
+  end
+
+  desc "create", "Create a build setup"
+  def create
+    if (remote_host = KAMAL.config.builder.remote_host)
+      connect_to_remote_host(remote_host)
+    end
+
+    run_locally do
+      begin
+        debug "Using builder: #{KAMAL.builder.name}"
+        execute *KAMAL.builder.create
+      rescue SSHKit::Command::Failed => e
+        if e.message =~ /stderr=(.*)/
+          error "Couldn't create remote builder: #{$1}"
+          false
+        else
+          raise
+        end
+      end
+    end
+  end
+
+  desc "remove", "Remove build setup"
+  def remove
+    run_locally do
+      debug "Using builder: #{KAMAL.builder.name}"
+      execute *KAMAL.builder.remove
+    end
+  end
+
+  desc "details", "Show build setup"
+  def details
+    run_locally do
+      puts "Builder: #{KAMAL.builder.name}"
+      puts capture(*KAMAL.builder.info)
+    end
+  end
+
+  private
+    def verify_local_dependencies
+      run_locally do
+        begin
+          execute *KAMAL.builder.ensure_local_dependencies_installed
+        rescue SSHKit::Command::Failed => e
+          build_error = e.message =~ /command not found/ ?
+            "Docker is not installed locally" :
+            "Docker buildx plugin is not installed locally"
+
+          raise BuildError, build_error
+        end
+      end
+    end
+
+    def connect_to_remote_host(remote_host)
+      remote_uri = URI.parse(remote_host)
+      if remote_uri.scheme == "ssh"
+        host = SSHKit::Host.new(
+          hostname: remote_uri.host,
+          ssh_options: { user: remote_uri.user, port: remote_uri.port }.compact
+        )
+        on(host, options) do
+          execute "true"
+        end
+      end
+    end
+
+    def mirror_hosts
+      if KAMAL.hosts.many?
+        mirror_hosts = Concurrent::Hash.new
+        on(KAMAL.hosts) do |host|
+          first_mirror = capture_with_info(*KAMAL.builder.first_mirror).strip.presence
+          mirror_hosts[first_mirror] ||= host.to_s if first_mirror
+        rescue SSHKit::Command::Failed => e
+          raise unless e.message =~ /error calling index: reflect: slice index out of range/
+        end
+        mirror_hosts.values
+      else
+        []
+      end
+    end
+
+    def pull_on_hosts(hosts)
+      on(hosts) do
+        execute *KAMAL.auditor.record("Pulled image with version #{KAMAL.config.version}"), verbosity: :debug
+        execute *KAMAL.builder.clean, raise_on_non_zero_exit: false
+        execute *KAMAL.builder.pull
+        execute *KAMAL.builder.validate_image
+      end
+    end
+end

lib/kamal/cli/build/clone.rb

@@ -0,0 +1,61 @@
+require "uri"
+
+class Kamal::Cli::Build::Clone
+  attr_reader :sshkit
+  delegate :info, :error, :execute, :capture_with_info, to: :sshkit
+
+  def initialize(sshkit)
+    @sshkit = sshkit
+  end
+
+  def prepare
+    begin
+      clone_repo
+    rescue SSHKit::Command::Failed => e
+      if e.message =~ /already exists and is not an empty directory/
+        reset
+      else
+        raise Kamal::Cli::Build::BuildError, "Failed to clone repo: #{e.message}"
+      end
+    end
+
+    validate!
+  rescue Kamal::Cli::Build::BuildError => e
+    error "Error preparing clone: #{e.message}, deleting and retrying..."
+
+    FileUtils.rm_rf KAMAL.config.builder.clone_directory
+    clone_repo
+    validate!
+  end
+
+  private
+    def clone_repo
+      info "Cloning repo into build directory `#{KAMAL.config.builder.build_directory}`..."
+
+      FileUtils.mkdir_p KAMAL.config.builder.clone_directory
+      execute *KAMAL.builder.clone
+    end
+
+    def reset
+      info "Resetting local clone as `#{KAMAL.config.builder.build_directory}` already exists..."
+
+      KAMAL.builder.clone_reset_steps.each { |step| execute *step }
+    rescue SSHKit::Command::Failed => e
+      raise Kamal::Cli::Build::BuildError, "Failed to clone repo: #{e.message}"
+    end
+
+    def validate!
+      status = capture_with_info(*KAMAL.builder.clone_status).strip
+
+      unless status.empty?
+        raise Kamal::Cli::Build::BuildError, "Clone in #{KAMAL.config.builder.build_directory} is dirty, #{status}"
+      end
+
+      revision = capture_with_info(*KAMAL.builder.clone_revision).strip
+      if revision != Kamal::Git.revision
+        raise Kamal::Cli::Build::BuildError, "Clone in #{KAMAL.config.builder.build_directory} is not on the correct revision, expected `#{Kamal::Git.revision}` but got `#{revision}`"
+      end
+    rescue SSHKit::Command::Failed => e
+      raise Kamal::Cli::Build::BuildError, "Failed to validate clone: #{e.message}"
+    end
+end

lib/kamal/cli/env.rb

@@ -0,0 +1,54 @@
+require "tempfile"
+
+class Kamal::Cli::Env < Kamal::Cli::Base
+  desc "push", "Push the env file to the remote hosts"
+  def push
+    with_lock do
+      on(KAMAL.hosts) do
+        execute *KAMAL.auditor.record("Pushed env files"), verbosity: :debug
+
+        KAMAL.roles_on(host).each do |role|
+          execute *KAMAL.app(role: role, host: host).make_env_directory
+          upload! role.env(host).secrets_io, role.env(host).secrets_file, mode: 400
+        end
+      end
+
+      on(KAMAL.traefik_hosts) do
+        execute *KAMAL.traefik.make_env_directory
+        upload! KAMAL.traefik.env.secrets_io, KAMAL.traefik.env.secrets_file, mode: 400
+      end
+
+      on(KAMAL.accessory_hosts) do
+        KAMAL.accessories_on(host).each do |accessory|
+          accessory_config = KAMAL.config.accessory(accessory)
+          execute *KAMAL.accessory(accessory).make_env_directory
+          upload! accessory_config.env.secrets_io, accessory_config.env.secrets_file, mode: 400
+        end
+      end
+    end
+  end
+
+  desc "delete", "Delete the env file from the remote hosts"
+  def delete
+    with_lock do
+      on(KAMAL.hosts) do
+        execute *KAMAL.auditor.record("Deleted env files"), verbosity: :debug
+
+        KAMAL.roles_on(host).each do |role|
+          execute *KAMAL.app(role: role, host: host).remove_env_file
+        end
+      end
+
+      on(KAMAL.traefik_hosts) do
+        execute *KAMAL.traefik.remove_env_file
+      end
+
+      on(KAMAL.accessory_hosts) do
+        KAMAL.accessories_on(host).each do |accessory|
+          accessory_config = KAMAL.config.accessory(accessory)
+          execute *KAMAL.accessory(accessory).remove_env_file
+        end
+      end
+    end
+  end
+end

lib/kamal/cli/healthcheck/barrier.rb

@@ -0,0 +1,31 @@
+class Kamal::Cli::Healthcheck::Barrier
+  def initialize
+    @ivar = Concurrent::IVar.new
+  end
+
+  def close
+    set(false)
+  end
+
+  def open
+    set(true)
+  end
+
+  def wait
+    unless opened?
+      raise Kamal::Cli::Healthcheck::Error.new("Halted at barrier")
+    end
+  end
+
+  private
+    def opened?
+      @ivar.value
+    end
+
+    def set(value)
+      @ivar.set(value)
+      true
+    rescue Concurrent::MultipleAssignmentError
+      false
+    end
+end

lib/kamal/cli/healthcheck/error.rb

@@ -0,0 +1,2 @@
+class Kamal::Cli::Healthcheck::Error < StandardError
+end

lib/kamal/cli/healthcheck/poller.rb

@@ -0,0 +1,63 @@
+module Kamal::Cli::Healthcheck::Poller
+  extend self
+
+  TRAEFIK_UPDATE_DELAY = 5
+
+
+  def wait_for_healthy(pause_after_ready: false, &block)
+    attempt = 1
+    max_attempts = KAMAL.config.healthcheck.max_attempts
+
+    begin
+      case status = block.call
+      when "healthy"
+        sleep TRAEFIK_UPDATE_DELAY if pause_after_ready
+      when "running" # No health check configured
+        sleep KAMAL.config.readiness_delay if pause_after_ready
+      else
+        raise Kamal::Cli::Healthcheck::Error, "container not ready (#{status})"
+      end
+    rescue Kamal::Cli::Healthcheck::Error => e
+      if attempt <= max_attempts
+        info "#{e.message}, retrying in #{attempt}s (attempt #{attempt}/#{max_attempts})..."
+        sleep attempt
+        attempt += 1
+        retry
+      else
+        raise
+      end
+    end
+
+    info "Container is healthy!"
+  end
+
+  def wait_for_unhealthy(pause_after_ready: false, &block)
+    attempt = 1
+    max_attempts = KAMAL.config.healthcheck.max_attempts
+
+    begin
+      case status = block.call
+      when "unhealthy"
+        sleep TRAEFIK_UPDATE_DELAY if pause_after_ready
+      else
+        raise Kamal::Cli::Healthcheck::Error, "container not unhealthy (#{status})"
+      end
+    rescue Kamal::Cli::Healthcheck::Error => e
+      if attempt <= max_attempts
+        info "#{e.message}, retrying in #{attempt}s (attempt #{attempt}/#{max_attempts})..."
+        sleep attempt
+        attempt += 1
+        retry
+      else
+        raise
+      end
+    end
+
+    info "Container is unhealthy!"
+  end
+
+  private
+    def info(message)
+      SSHKit.config.output.info(message)
+    end
+end

lib/kamal/cli/lock.rb

@@ -0,0 +1,46 @@
+class Kamal::Cli::Lock < Kamal::Cli::Base
+  desc "status", "Report lock status"
+  def status
+    handle_missing_lock do
+      on(KAMAL.primary_host) do
+        execute *KAMAL.server.ensure_run_directory
+        puts capture_with_debug(*KAMAL.lock.status)
+      end
+    end
+  end
+
+  desc "acquire", "Acquire the deploy lock"
+  option :message, aliases: "-m", type: :string, desc: "A lock message", required: true
+  def acquire
+    message = options[:message]
+    raise_if_locked do
+      on(KAMAL.primary_host) do
+        execute *KAMAL.server.ensure_run_directory
+        execute *KAMAL.lock.acquire(message, KAMAL.config.version), verbosity: :debug
+      end
+      say "Acquired the deploy lock"
+    end
+  end
+
+  desc "release", "Release the deploy lock"
+  def release
+    handle_missing_lock do
+      on(KAMAL.primary_host) do
+        execute *KAMAL.server.ensure_run_directory
+        execute *KAMAL.lock.release, verbosity: :debug
+      end
+      say "Released the deploy lock"
+    end
+  end
+
+  private
+    def handle_missing_lock
+      yield
+    rescue SSHKit::Runner::ExecuteError => e
+      if e.message =~ /No such file or directory/
+        say "There is no deploy lock"
+      else
+        raise
+      end
+    end
+end

lib/kamal/cli/main.rb

@@ -0,0 +1,250 @@
+class Kamal::Cli::Main < Kamal::Cli::Base
+  desc "setup", "Setup all accessories, push the env, and deploy app to servers"
+  option :skip_push, aliases: "-P", type: :boolean, default: false, desc: "Skip image build and push"
+  def setup
+    print_runtime do
+      with_lock do
+        invoke_options = deploy_options
+
+        say "Ensure Docker is installed...", :magenta
+        invoke "kamal:cli:server:bootstrap", [], invoke_options
+
+        say "Evaluate and push env files...", :magenta
+        invoke "kamal:cli:env:push", [], invoke_options
+
+        invoke "kamal:cli:accessory:boot", [ "all" ], invoke_options
+        deploy
+      end
+    end
+  end
+
+  desc "deploy", "Deploy app to servers"
+  option :skip_push, aliases: "-P", type: :boolean, default: false, desc: "Skip image build and push"
+  def deploy
+    runtime = print_runtime do
+      invoke_options = deploy_options
+
+      say "Log into image registry...", :magenta
+      invoke "kamal:cli:registry:login", [], invoke_options.merge(skip_local: options[:skip_push])
+
+      if options[:skip_push]
+        say "Pull app image...", :magenta
+        invoke "kamal:cli:build:pull", [], invoke_options
+      else
+        say "Build and push app image...", :magenta
+        invoke "kamal:cli:build:deliver", [], invoke_options
+      end
+
+      with_lock do
+        run_hook "pre-deploy"
+
+        say "Ensure Traefik is running...", :magenta
+        invoke "kamal:cli:traefik:boot", [], invoke_options
+
+        say "Detect stale containers...", :magenta
+        invoke "kamal:cli:app:stale_containers", [], invoke_options.merge(stop: true)
+
+        invoke "kamal:cli:app:boot", [], invoke_options
+
+        say "Prune old containers and images...", :magenta
+        invoke "kamal:cli:prune:all", [], invoke_options
+      end
+    end
+
+    run_hook "post-deploy", runtime: runtime.round
+  end
+
+  desc "redeploy", "Deploy app to servers without bootstrapping servers, starting Traefik, pruning, and registry login"
+  option :skip_push, aliases: "-P", type: :boolean, default: false, desc: "Skip image build and push"
+  def redeploy
+    runtime = print_runtime do
+      invoke_options = deploy_options
+
+      if options[:skip_push]
+        say "Pull app image...", :magenta
+        invoke "kamal:cli:build:pull", [], invoke_options
+      else
+        say "Build and push app image...", :magenta
+        invoke "kamal:cli:build:deliver", [], invoke_options
+      end
+
+      with_lock do
+        run_hook "pre-deploy"
+
+        say "Detect stale containers...", :magenta
+        invoke "kamal:cli:app:stale_containers", [], invoke_options.merge(stop: true)
+
+        invoke "kamal:cli:app:boot", [], invoke_options
+      end
+    end
+
+    run_hook "post-deploy", runtime: runtime.round
+  end
+
+  desc "rollback [VERSION]", "Rollback app to VERSION"
+  def rollback(version)
+    rolled_back = false
+    runtime = print_runtime do
+      with_lock do
+        invoke_options = deploy_options
+
+        KAMAL.config.version = version
+        old_version = nil
+
+        if container_available?(version)
+          run_hook "pre-deploy"
+
+          invoke "kamal:cli:app:boot", [], invoke_options.merge(version: version)
+          rolled_back = true
+        else
+          say "The app version '#{version}' is not available as a container (use 'kamal app containers' for available versions)", :red
+        end
+      end
+    end
+
+    run_hook "post-deploy", runtime: runtime.round if rolled_back
+  end
+
+  desc "details", "Show details about all containers"
+  def details
+    invoke "kamal:cli:traefik:details"
+    invoke "kamal:cli:app:details"
+    invoke "kamal:cli:accessory:details", [ "all" ]
+  end
+
+  desc "audit", "Show audit log from servers"
+  def audit
+    on(KAMAL.hosts) do |host|
+      puts_by_host host, capture_with_info(*KAMAL.auditor.reveal)
+    end
+  end
+
+  desc "config", "Show combined config (including secrets!)"
+  def config
+    run_locally do
+      puts Kamal::Utils.redacted(KAMAL.config.to_h).to_yaml
+    end
+  end
+
+  desc "docs", "Show Kamal documentation for configuration setting"
+  def docs(section = nil)
+    case section
+    when NilClass
+      puts Kamal::Configuration.validation_doc
+    else
+      puts Kamal::Configuration.const_get(section.titlecase.to_sym).validation_doc
+    end
+  rescue NameError
+    puts "No documentation found for #{section}"
+  end
+
+  desc "init", "Create config stub in config/deploy.yml and env stub in .env"
+  option :bundle, type: :boolean, default: false, desc: "Add Kamal to the Gemfile and create a bin/kamal binstub"
+  def init
+    require "fileutils"
+
+    if (deploy_file = Pathname.new(File.expand_path("config/deploy.yml"))).exist?
+      puts "Config file already exists in config/deploy.yml (remove first to create a new one)"
+    else
+      FileUtils.mkdir_p deploy_file.dirname
+      FileUtils.cp_r Pathname.new(File.expand_path("templates/deploy.yml", __dir__)), deploy_file
+      puts "Created configuration file in config/deploy.yml"
+    end
+
+    unless (deploy_file = Pathname.new(File.expand_path(".env"))).exist?
+      FileUtils.cp_r Pathname.new(File.expand_path("templates/template.env", __dir__)), deploy_file
+      puts "Created .env file"
+    end
+
+    unless (hooks_dir = Pathname.new(File.expand_path(".kamal/hooks"))).exist?
+      hooks_dir.mkpath
+      Pathname.new(File.expand_path("templates/sample_hooks", __dir__)).each_child do |sample_hook|
+        FileUtils.cp sample_hook, hooks_dir, preserve: true
+      end
+      puts "Created sample hooks in .kamal/hooks"
+    end
+
+    if options[:bundle]
+      if (binstub = Pathname.new(File.expand_path("bin/kamal"))).exist?
+        puts "Binstub already exists in bin/kamal (remove first to create a new one)"
+      else
+        puts "Adding Kamal to Gemfile and bundle..."
+        run_locally do
+          execute :bundle, :add, :kamal
+          execute :bundle, :binstubs, :kamal
+        end
+        puts "Created binstub file in bin/kamal"
+      end
+    end
+  end
+
+  desc "remove", "Remove Traefik, app, accessories, and registry session from servers"
+  option :confirmed, aliases: "-y", type: :boolean, default: false, desc: "Proceed without confirmation question"
+  def remove
+    confirming "This will remove all containers and images. Are you sure?" do
+      with_lock do
+        invoke "kamal:cli:traefik:remove", [], options.without(:confirmed)
+        invoke "kamal:cli:app:remove", [], options.without(:confirmed)
+        invoke "kamal:cli:accessory:remove", [ "all" ], options
+        invoke "kamal:cli:registry:logout", [], options.without(:confirmed).merge(skip_local: true)
+      end
+    end
+  end
+
+  desc "version", "Show Kamal version"
+  def version
+    puts Kamal::VERSION
+  end
+
+  desc "accessory", "Manage accessories (db/redis/search)"
+  subcommand "accessory", Kamal::Cli::Accessory
+
+  desc "app", "Manage application"
+  subcommand "app", Kamal::Cli::App
+
+  desc "build", "Build application image"
+  subcommand "build", Kamal::Cli::Build
+
+  desc "env", "Manage environment files"
+  subcommand "env", Kamal::Cli::Env
+
+  desc "lock", "Manage the deploy lock"
+  subcommand "lock", Kamal::Cli::Lock
+
+  desc "prune", "Prune old application images and containers"
+  subcommand "prune", Kamal::Cli::Prune
+
+  desc "registry", "Login and -out of the image registry"
+  subcommand "registry", Kamal::Cli::Registry
+
+  desc "server", "Bootstrap servers with curl and Docker"
+  subcommand "server", Kamal::Cli::Server
+
+  desc "traefik", "Manage Traefik load balancer"
+  subcommand "traefik", Kamal::Cli::Traefik
+
+  private
+    def container_available?(version)
+      begin
+        on(KAMAL.hosts) do
+          KAMAL.roles_on(host).each do |role|
+            container_id = capture_with_info(*KAMAL.app(role: role, host: host).container_id_for_version(version))
+            raise "Container not found" unless container_id.present?
+          end
+        end
+      rescue SSHKit::Runner::ExecuteError, SSHKit::Runner::MultipleExecuteError => e
+        if e.message =~ /Container not found/
+          say "Error looking for container version #{version}: #{e.message}"
+          return false
+        else
+          raise
+        end
+      end
+
+      true
+    end
+
+    def deploy_options
+      { "version" => KAMAL.config.version }.merge(options.without("skip_push"))
+    end
+end

lib/kamal/cli/prune.rb

@@ -0,0 +1,35 @@
+class Kamal::Cli::Prune < Kamal::Cli::Base
+  desc "all", "Prune unused images and stopped containers"
+  def all
+    with_lock do
+      containers
+      images
+    end
+  end
+
+  desc "images", "Prune unused images"
+  def images
+    with_lock do
+      on(KAMAL.hosts) do
+        execute *KAMAL.auditor.record("Pruned images"), verbosity: :debug
+        execute *KAMAL.prune.dangling_images
+        execute *KAMAL.prune.tagged_images
+      end
+    end
+  end
+
+  desc "containers", "Prune all stopped containers, except the last n (default 5)"
+  option :retain, type: :numeric, default: nil, desc: "Number of containers to retain"
+  def containers
+    retain = options.fetch(:retain, KAMAL.config.retain_containers)
+    raise "retain must be at least 1" if retain < 1
+
+    with_lock do
+      on(KAMAL.hosts) do
+        execute *KAMAL.auditor.record("Pruned containers"), verbosity: :debug
+        execute *KAMAL.prune.app_containers(retain: retain)
+        execute *KAMAL.prune.healthcheck_containers
+      end
+    end
+  end
+end

lib/kamal/cli/registry.rb

@@ -0,0 +1,17 @@
+class Kamal::Cli::Registry < Kamal::Cli::Base
+  desc "login", "Log in to registry locally and remotely"
+  option :skip_local, aliases: "-L", type: :boolean, default: false, desc: "Skip local login"
+  option :skip_remote, aliases: "-R", type: :boolean, default: false, desc: "Skip remote login"
+  def login
+    run_locally    { execute *KAMAL.registry.login } unless options[:skip_local]
+    on(KAMAL.hosts) { execute *KAMAL.registry.login } unless options[:skip_remote]
+  end
+
+  desc "logout", "Log out of registry locally and remotely"
+  option :skip_local, aliases: "-L", type: :boolean, default: false, desc: "Skip local login"
+  option :skip_remote, aliases: "-R", type: :boolean, default: false, desc: "Skip remote login"
+  def logout
+    run_locally    { execute *KAMAL.registry.logout } unless options[:skip_local]
+    on(KAMAL.hosts) { execute *KAMAL.registry.logout } unless options[:skip_remote]
+  end
+end

lib/kamal/cli/server.rb

@@ -0,0 +1,49 @@
+class Kamal::Cli::Server < Kamal::Cli::Base
+  desc "exec", "Run a custom command on the server (use --help to show options)"
+  option :interactive, type: :boolean, aliases: "-i", default: false, desc: "Run the command interactively (use for console/bash)"
+  def exec(cmd)
+    hosts = KAMAL.hosts | KAMAL.accessory_hosts
+
+    case
+    when options[:interactive]
+      host = KAMAL.primary_host
+
+      say "Running '#{cmd}' on #{host} interactively...", :magenta
+
+      run_locally { exec KAMAL.server.run_over_ssh(cmd, host: host) }
+    else
+      say "Running '#{cmd}' on #{hosts.join(', ')}...", :magenta
+
+      on(hosts) do |host|
+        execute *KAMAL.auditor.record("Executed cmd '#{cmd}' on #{host}"), verbosity: :debug
+        puts_by_host host, capture_with_info(cmd)
+      end
+    end
+  end
+
+  desc "bootstrap", "Set up Docker to run Kamal apps"
+  def bootstrap
+    with_lock do
+      missing = []
+
+      on(KAMAL.hosts | KAMAL.accessory_hosts) do |host|
+        unless execute(*KAMAL.docker.installed?, raise_on_non_zero_exit: false)
+          if execute(*KAMAL.docker.superuser?, raise_on_non_zero_exit: false)
+            info "Missing Docker on #{host}. Installing…"
+            execute *KAMAL.docker.install
+          else
+            missing << host
+          end
+        end
+
+        execute(*KAMAL.server.ensure_run_directory)
+      end
+
+      if missing.any?
+        raise "Docker is not installed on #{missing.join(", ")} and can't be automatically installed without having root access and either `wget` or `curl`. Install Docker manually: https://docs.docker.com/engine/install/"
+      end
+
+      run_hook "docker-setup"
+    end
+  end
+end

lib/kamal/cli/templates/deploy.yml

@@ -0,0 +1,101 @@
+# Name of your application. Used to uniquely configure containers.
+service: my-app
+
+# Name of the container image.
+image: user/my-app
+
+# Deploy to these servers.
+servers:
+  - 192.168.0.1
+
+# Credentials for your image host.
+registry:
+  # Specify the registry server, if you're not using Docker Hub
+  # server: registry.digitalocean.com / ghcr.io / ...
+  username: my-user
+
+  # Always use an access token rather than real password when possible.
+  password:
+    - KAMAL_REGISTRY_PASSWORD
+
+# Inject ENV variables into containers (secrets come from .env).
+# Remember to run `kamal env push` after making changes!
+# env:
+#   clear:
+#     DB_HOST: 192.168.0.2
+#   secret:
+#     - RAILS_MASTER_KEY
+
+# Use a different ssh user than root
+# ssh:
+#   user: app
+
+# Configure builder setup.
+# builder:
+#   args:
+#     RUBY_VERSION: 3.2.0
+#   secrets:
+#     - GITHUB_TOKEN
+#   remote:
+#     arch: amd64
+#     host: ssh://app@192.168.0.1
+
+# Use accessory services (secrets come from .env).
+# accessories:
+#   db:
+#     image: mysql:8.0
+#     host: 192.168.0.2
+#     port: 3306
+#     env:
+#       clear:
+#         MYSQL_ROOT_HOST: '%'
+#       secret:
+#         - MYSQL_ROOT_PASSWORD
+#     files:
+#       - config/mysql/production.cnf:/etc/mysql/my.cnf
+#       - db/production.sql:/docker-entrypoint-initdb.d/setup.sql
+#     directories:
+#       - data:/var/lib/mysql
+#   redis:
+#     image: redis:7.0
+#     host: 192.168.0.2
+#     port: 6379
+#     directories:
+#       - data:/data
+
+# Configure custom arguments for Traefik. Be sure to reboot traefik when you modify it.
+# traefik:
+#   args:
+#     accesslog: true
+#     accesslog.format: json
+
+# Configure a custom healthcheck (default is /up on port 3000)
+# healthcheck:
+#   path: /healthz
+#   port: 4000
+
+# Bridge fingerprinted assets, like JS and CSS, between versions to avoid
+# hitting 404 on in-flight requests. Combines all files from new and old
+# version inside the asset_path.
+#
+# If your app is using the Sprockets gem, ensure it sets `config.assets.manifest`.
+# See https://github.com/basecamp/kamal/issues/626 for details
+#
+# asset_path: /rails/public/assets
+
+# Configure rolling deploys by setting a wait time between batches of restarts.
+# boot:
+#   limit: 10 # Can also specify as a percentage of total hosts, such as "25%"
+#   wait: 2
+
+# Configure the role used to determine the primary_host. This host takes
+# deploy locks, runs health checks during the deploy, and follow logs, etc.
+#
+# Caution: there's no support for role renaming yet, so be careful to cleanup
+#          the previous role on the deployed hosts.
+# primary_role: web
+
+# Controls if we abort when see a role with no hosts. Disabling this may be
+# useful for more complex deploy configurations.
+#
+# allow_empty_roles: false

lib/kamal/cli/templates/sample_hooks/docker-setup.sample

@@ -0,0 +1,13 @@
+#!/usr/bin/env ruby
+
+# A sample docker-setup hook
+#
+# Sets up a Docker network on defined hosts which can then be used by the application’s containers
+
+hosts = ENV["KAMAL_HOSTS"].split(",")
+
+hosts.each do |ip|
+  destination = "root@#{ip}"
+  puts "Creating a Docker network \"kamal\" on #{destination}"
+  `ssh #{destination} docker network create kamal`
+end

lib/kamal/cli/templates/sample_hooks/post-deploy.sample

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+# A sample post-deploy hook
+#
+# These environment variables are available:
+# KAMAL_RECORDED_AT
+# KAMAL_PERFORMER
+# KAMAL_VERSION
+# KAMAL_HOSTS
+# KAMAL_ROLE (if set)
+# KAMAL_DESTINATION (if set)
+# KAMAL_RUNTIME
+
+echo "$KAMAL_PERFORMER deployed $KAMAL_VERSION to $KAMAL_DESTINATION in $KAMAL_RUNTIME seconds"

lib/kamal/cli/templates/sample_hooks/post-traefik-reboot.sample

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+echo "Rebooted Traefik on $KAMAL_HOSTS"

lib/kamal/cli/templates/sample_hooks/pre-build.sample

@@ -0,0 +1,51 @@
+#!/bin/sh
+
+# A sample pre-build hook
+#
+# Checks:
+# 1. We have a clean checkout
+# 2. A remote is configured
+# 3. The branch has been pushed to the remote
+# 4. The version we are deploying matches the remote
+#
+# These environment variables are available:
+# KAMAL_RECORDED_AT
+# KAMAL_PERFORMER
+# KAMAL_VERSION
+# KAMAL_HOSTS
+# KAMAL_ROLE (if set)
+# KAMAL_DESTINATION (if set)
+
+if [ -n "$(git status --porcelain)" ]; then
+  echo "Git checkout is not clean, aborting..." >&2
+  git status --porcelain >&2
+  exit 1
+fi
+
+first_remote=$(git remote)
+
+if [ -z "$first_remote" ]; then
+  echo "No git remote set, aborting..." >&2
+  exit 1
+fi
+
+current_branch=$(git branch --show-current)
+
+if [ -z "$current_branch" ]; then
+  echo "Not on a git branch, aborting..." >&2
+  exit 1
+fi
+
+remote_head=$(git ls-remote $first_remote --tags $current_branch | cut -f1)
+
+if [ -z "$remote_head" ]; then
+  echo "Branch not pushed to remote, aborting..." >&2
+  exit 1
+fi
+
+if [ "$KAMAL_VERSION" != "$remote_head" ]; then
+  echo "Version ($KAMAL_VERSION) does not match remote HEAD ($remote_head), aborting..." >&2
+  exit 1
+fi
+
+exit 0

lib/kamal/cli/templates/sample_hooks/pre-connect.sample

@@ -0,0 +1,47 @@
+#!/usr/bin/env ruby
+
+# A sample pre-connect check
+#
+# Warms DNS before connecting to hosts in parallel
+#
+# These environment variables are available:
+# KAMAL_RECORDED_AT
+# KAMAL_PERFORMER
+# KAMAL_VERSION
+# KAMAL_HOSTS
+# KAMAL_ROLE (if set)
+# KAMAL_DESTINATION (if set)
+# KAMAL_RUNTIME
+
+hosts = ENV["KAMAL_HOSTS"].split(",")
+results = nil
+max = 3
+
+elapsed = Benchmark.realtime do
+  results = hosts.map do |host|
+    Thread.new do
+      tries = 1
+
+      begin
+        Socket.getaddrinfo(host, 0, Socket::AF_UNSPEC, Socket::SOCK_STREAM, nil, Socket::AI_CANONNAME)
+      rescue SocketError
+        if tries < max
+          puts "Retrying DNS warmup: #{host}"
+          tries += 1
+          sleep rand
+          retry
+        else
+          puts "DNS warmup failed: #{host}"
+          host
+        end
+      end
+
+      tries
+    end
+  end.map(&:value)
+end
+
+retries = results.sum - hosts.size
+nopes = results.count { |r| r == max }
+
+puts "Prewarmed %d DNS lookups in %.2f sec: %d retries, %d failures" % [ hosts.size, elapsed, retries, nopes ]

lib/kamal/cli/templates/sample_hooks/pre-deploy.sample

@@ -0,0 +1,109 @@
+#!/usr/bin/env ruby
+
+# A sample pre-deploy hook
+#
+# Checks the Github status of the build, waiting for a pending build to complete for up to 720 seconds.
+#
+# Fails unless the combined status is "success"
+#
+# These environment variables are available:
+# KAMAL_RECORDED_AT
+# KAMAL_PERFORMER
+# KAMAL_VERSION
+# KAMAL_HOSTS
+# KAMAL_COMMAND
+# KAMAL_SUBCOMMAND
+# KAMAL_ROLE (if set)
+# KAMAL_DESTINATION (if set)
+
+# Only check the build status for production deployments
+if ENV["KAMAL_COMMAND"] == "rollback" || ENV["KAMAL_DESTINATION"] != "production"
+  exit 0
+end
+
+require "bundler/inline"
+
+# true = install gems so this is fast on repeat invocations
+gemfile(true, quiet: true) do
+  source "https://rubygems.org"
+
+  gem "octokit"
+  gem "faraday-retry"
+end
+
+MAX_ATTEMPTS = 72
+ATTEMPTS_GAP = 10
+
+def exit_with_error(message)
+  $stderr.puts message
+  exit 1
+end
+
+class GithubStatusChecks
+  attr_reader :remote_url, :git_sha, :github_client, :combined_status
+
+  def initialize
+    @remote_url = `git config --get remote.origin.url`.strip.delete_prefix("https://github.com/")
+    @git_sha = `git rev-parse HEAD`.strip
+    @github_client = Octokit::Client.new(access_token: ENV["GITHUB_TOKEN"])
+    refresh!
+  end
+
+  def refresh!
+    @combined_status = github_client.combined_status(remote_url, git_sha)
+  end
+
+  def state
+    combined_status[:state]
+  end
+
+  def first_status_url
+    first_status = combined_status[:statuses].find { |status| status[:state] == state }
+    first_status && first_status[:target_url]
+  end
+
+  def complete_count
+    combined_status[:statuses].count { |status| status[:state] != "pending"}
+  end
+
+  def total_count
+    combined_status[:statuses].count
+  end
+
+  def current_status
+    if total_count > 0
+      "Completed #{complete_count}/#{total_count} checks, see #{first_status_url} ..."
+    else
+      "Build not started..."
+    end
+  end
+end
+
+
+$stdout.sync = true
+
+puts "Checking build status..."
+attempts = 0
+checks = GithubStatusChecks.new
+
+begin
+  loop do
+    case checks.state
+    when "success"
+      puts "Checks passed, see #{checks.first_status_url}"
+      exit 0
+    when "failure"
+      exit_with_error "Checks failed, see #{checks.first_status_url}"
+    when "pending"
+      attempts += 1
+    end
+
+    exit_with_error "Checks are still pending, gave up after #{MAX_ATTEMPTS * ATTEMPTS_GAP} seconds" if attempts == MAX_ATTEMPTS
+
+    puts checks.current_status
+    sleep(ATTEMPTS_GAP)
+    checks.refresh!
+  end
+rescue Octokit::NotFound
+  exit_with_error "Build status could not be found"
+end

lib/kamal/cli/templates/sample_hooks/pre-traefik-reboot.sample

@@ -0,0 +1,3 @@
+#!/bin/sh
+
+echo "Rebooting Traefik on $KAMAL_HOSTS..."

lib/kamal/cli/templates/template.env

@@ -0,0 +1,2 @@
+KAMAL_REGISTRY_PASSWORD=change-this
+RAILS_MASTER_KEY=another-env

lib/kamal/cli/traefik.rb

@@ -0,0 +1,122 @@
+class Kamal::Cli::Traefik < Kamal::Cli::Base
+  desc "boot", "Boot Traefik on servers"
+  def boot
+    with_lock do
+      on(KAMAL.traefik_hosts) do
+        execute *KAMAL.registry.login
+        execute *KAMAL.traefik.start_or_run
+      end
+    end
+  end
+
+  desc "reboot", "Reboot Traefik on servers (stop container, remove container, start new container)"
+  option :rolling, type: :boolean, default: false, desc: "Reboot traefik on hosts in sequence, rather than in parallel"
+  option :confirmed, aliases: "-y", type: :boolean, default: false, desc: "Proceed without confirmation question"
+  def reboot
+    confirming "This will cause a brief outage on each host. Are you sure?" do
+      with_lock do
+        host_groups = options[:rolling] ? KAMAL.traefik_hosts : [ KAMAL.traefik_hosts ]
+        host_groups.each do |hosts|
+          host_list = Array(hosts).join(",")
+          run_hook "pre-traefik-reboot", hosts: host_list
+          on(hosts) do
+            execute *KAMAL.auditor.record("Rebooted traefik"), verbosity: :debug
+            execute *KAMAL.registry.login
+            execute *KAMAL.traefik.stop, raise_on_non_zero_exit: false
+            execute *KAMAL.traefik.remove_container
+            execute *KAMAL.traefik.run
+          end
+          run_hook "post-traefik-reboot", hosts: host_list
+        end
+      end
+    end
+  end
+
+  desc "start", "Start existing Traefik container on servers"
+  def start
+    with_lock do
+      on(KAMAL.traefik_hosts) do
+        execute *KAMAL.auditor.record("Started traefik"), verbosity: :debug
+        execute *KAMAL.traefik.start
+      end
+    end
+  end
+
+  desc "stop", "Stop existing Traefik container on servers"
+  def stop
+    with_lock do
+      on(KAMAL.traefik_hosts) do
+        execute *KAMAL.auditor.record("Stopped traefik"), verbosity: :debug
+        execute *KAMAL.traefik.stop, raise_on_non_zero_exit: false
+      end
+    end
+  end
+
+  desc "restart", "Restart existing Traefik container on servers"
+  def restart
+    with_lock do
+      stop
+      start
+    end
+  end
+
+  desc "details", "Show details about Traefik container from servers"
+  def details
+    on(KAMAL.traefik_hosts) { |host| puts_by_host host, capture_with_info(*KAMAL.traefik.info), type: "Traefik" }
+  end
+
+  desc "logs", "Show log lines from Traefik on servers"
+  option :since, aliases: "-s", desc: "Show logs since timestamp (e.g. 2013-01-02T13:23:37Z) or relative (e.g. 42m for 42 minutes)"
+  option :lines, type: :numeric, aliases: "-n", desc: "Number of log lines to pull from each server"
+  option :grep, aliases: "-g", desc: "Show lines with grep match only (use this to fetch specific requests by id)"
+  option :grep_options, aliases: "-o", desc: "Additional options supplied to grep"
+  option :follow, aliases: "-f", desc: "Follow logs on primary server (or specific host set by --hosts)"
+  def logs
+    grep = options[:grep]
+    grep_options = options[:grep_options]
+
+    if options[:follow]
+      run_locally do
+        info "Following logs on #{KAMAL.primary_host}..."
+        info KAMAL.traefik.follow_logs(host: KAMAL.primary_host, grep: grep, grep_options: grep_options)
+        exec KAMAL.traefik.follow_logs(host: KAMAL.primary_host, grep: grep, grep_options: grep_options)
+      end
+    else
+      since = options[:since]
+      lines = options[:lines].presence || ((since || grep) ? nil : 100) # Default to 100 lines if since or grep isn't set
+
+      on(KAMAL.traefik_hosts) do |host|
+        puts_by_host host, capture(*KAMAL.traefik.logs(since: since, lines: lines, grep: grep, grep_options: grep_options)), type: "Traefik"
+      end
+    end
+  end
+
+  desc "remove", "Remove Traefik container and image from servers"
+  def remove
+    with_lock do
+      stop
+      remove_container
+      remove_image
+    end
+  end
+
+  desc "remove_container", "Remove Traefik container from servers", hide: true
+  def remove_container
+    with_lock do
+      on(KAMAL.traefik_hosts) do
+        execute *KAMAL.auditor.record("Removed traefik container"), verbosity: :debug
+        execute *KAMAL.traefik.remove_container
+      end
+    end
+  end
+
+  desc "remove_image", "Remove Traefik image from servers", hide: true
+  def remove_image
+    with_lock do
+      on(KAMAL.traefik_hosts) do
+        execute *KAMAL.auditor.record("Removed traefik image"), verbosity: :debug
+        execute *KAMAL.traefik.remove_image
+      end
+    end
+  end
+end

lib/kamal/commander.rb

@@ -0,0 +1,160 @@
+require "active_support/core_ext/enumerable"
+require "active_support/core_ext/module/delegation"
+
+class Kamal::Commander
+  attr_accessor :verbosity, :holding_lock, :connected
+  delegate :hosts, :roles, :primary_host, :primary_role, :roles_on, :traefik_hosts, :accessory_hosts, to: :specifics
+
+  def initialize
+    self.verbosity = :info
+    self.holding_lock = false
+    self.connected = false
+    @specifics = nil
+  end
+
+  def config
+    @config ||= Kamal::Configuration.create_from(**@config_kwargs).tap do |config|
+      @config_kwargs = nil
+      configure_sshkit_with(config)
+    end
+  end
+
+  def configure(**kwargs)
+    @config, @config_kwargs = nil, kwargs
+  end
+
+  attr_reader :specific_roles, :specific_hosts
+
+  def specific_primary!
+    @specifics = nil
+    self.specific_hosts = [ config.primary_host ]
+  end
+
+  def specific_roles=(role_names)
+    @specifics = nil
+    if role_names.present?
+      @specific_roles = Kamal::Utils.filter_specific_items(role_names, config.roles)
+
+      if @specific_roles.empty?
+        raise ArgumentError, "No --roles match for #{role_names.join(',')}"
+      end
+
+      @specific_roles
+    end
+  end
+
+  def specific_hosts=(hosts)
+    @specifics = nil
+    if hosts.present?
+      @specific_hosts = Kamal::Utils.filter_specific_items(hosts, config.all_hosts)
+
+      if @specific_hosts.empty?
+        raise ArgumentError, "No --hosts match for #{hosts.join(',')}"
+      end
+
+      @specific_hosts
+    end
+  end
+
+  def accessory_names
+    config.accessories&.collect(&:name) || []
+  end
+
+  def accessories_on(host)
+    config.accessories.select { |accessory| accessory.hosts.include?(host.to_s) }.map(&:name)
+  end
+
+
+  def app(role: nil, host: nil)
+    Kamal::Commands::App.new(config, role: role, host: host)
+  end
+
+  def accessory(name)
+    Kamal::Commands::Accessory.new(config, name: name)
+  end
+
+  def auditor(**details)
+    Kamal::Commands::Auditor.new(config, **details)
+  end
+
+  def builder
+    @builder ||= Kamal::Commands::Builder.new(config)
+  end
+
+  def docker
+    @docker ||= Kamal::Commands::Docker.new(config)
+  end
+
+  def healthcheck
+    @healthcheck ||= Kamal::Commands::Healthcheck.new(config)
+  end
+
+  def hook
+    @hook ||= Kamal::Commands::Hook.new(config)
+  end
+
+  def lock
+    @lock ||= Kamal::Commands::Lock.new(config)
+  end
+
+  def prune
+    @prune ||= Kamal::Commands::Prune.new(config)
+  end
+
+  def registry
+    @registry ||= Kamal::Commands::Registry.new(config)
+  end
+
+  def server
+    @server ||= Kamal::Commands::Server.new(config)
+  end
+
+  def traefik
+    @traefik ||= Kamal::Commands::Traefik.new(config)
+  end
+
+
+  def with_verbosity(level)
+    old_level = self.verbosity
+
+    self.verbosity = level
+    SSHKit.config.output_verbosity = level
+
+    yield
+  ensure
+    self.verbosity = old_level
+    SSHKit.config.output_verbosity = old_level
+  end
+
+  def boot_strategy
+    if config.boot.limit.present?
+      { in: :groups, limit: config.boot.limit, wait: config.boot.wait }
+    else
+      {}
+    end
+  end
+
+  def holding_lock?
+    self.holding_lock
+  end
+
+  def connected?
+    self.connected
+  end
+
+  private
+    # Lazy setup of SSHKit
+    def configure_sshkit_with(config)
+      SSHKit::Backend::Netssh.pool.idle_timeout = config.sshkit.pool_idle_timeout
+      SSHKit::Backend::Netssh.configure do |sshkit|
+        sshkit.max_concurrent_starts = config.sshkit.max_concurrent_starts
+        sshkit.ssh_options = config.ssh.options
+      end
+      SSHKit.config.command_map[:docker] = "docker" # No need to use /usr/bin/env, just clogs up the logs
+      SSHKit.config.output_verbosity = verbosity
+    end
+
+    def specifics
+      @specifics ||= Kamal::Commander::Specifics.new(config, specific_hosts, specific_roles)
+    end
+end

lib/kamal/commander/specifics.rb

@@ -0,0 +1,49 @@
+class Kamal::Commander::Specifics
+  attr_reader :primary_host, :primary_role, :hosts, :roles
+  delegate :stable_sort!, to: Kamal::Utils
+
+  def initialize(config, specific_hosts, specific_roles)
+    @config, @specific_hosts, @specific_roles = config, specific_hosts, specific_roles
+
+    @roles, @hosts = specified_roles, specified_hosts
+
+    @primary_host = specific_hosts&.first || primary_specific_role&.primary_host || config.primary_host
+    @primary_role = primary_or_first_role(roles_on(primary_host))
+
+    stable_sort!(roles) { |role| role == primary_role ? 0 : 1 }
+    stable_sort!(hosts) { |host| roles_on(host).any? { |role| role == primary_role } ? 0 : 1 }
+  end
+
+  def roles_on(host)
+    roles.select { |role| role.hosts.include?(host.to_s) }
+  end
+
+  def traefik_hosts
+    config.traefik_hosts & specified_hosts
+  end
+
+  def accessory_hosts
+    specific_hosts || config.accessories.flat_map(&:hosts)
+  end
+
+  private
+    attr_reader :config, :specific_hosts, :specific_roles
+
+    def primary_specific_role
+      primary_or_first_role(specific_roles) if specific_roles.present?
+    end
+
+    def primary_or_first_role(roles)
+      roles.detect { |role| role == config.primary_role } || roles.first
+    end
+
+    def specified_roles
+      (specific_roles || config.roles) \
+        .select { |role| ((specific_hosts || config.all_hosts) & role.hosts).any? }
+    end
+
+    def specified_hosts
+      (specific_hosts || config.all_hosts) \
+        .select { |host| (specific_roles || config.roles).flat_map(&:hosts).include?(host) }
+    end
+end

lib/kamal/commands.rb

@@ -0,0 +1,2 @@
+module Kamal::Commands
+end

lib/kamal/commands/accessory.rb

@@ -1,6 +1,7 @@
-class Mrsk::Commands::Accessory < Mrsk::Commands::Base
+class Kamal::Commands::Accessory < Kamal::Commands::Base
   attr_reader :accessory_config
-  delegate :service_name, :image, :host, :port, :files, :directories, :env_args, :volume_args, :label_args, to: :accessory_config
+  delegate :service_name, :image, :hosts, :port, :files, :directories, :cmd,
+           :publish_args, :env_args, :volume_args, :label_args, :option_args, to: :accessory_config
 
   def initialize(config, name:)
     super(config)
@@ -10,14 +11,16 @@ class Mrsk::Commands::Accessory < Mrsk::Commands::Base
   def run
     docker :run,
       "--name", service_name,
-      "-d",
+      "--detach",
       "--restart", "unless-stopped",
-      "--log-opt", "max-size=#{MAX_LOG_SIZE}",
+      *config.logging_args,
-      "-p", port,
+      *publish_args,
       *env_args,
       *volume_args,
       *label_args,
-      image
+      *option_args,
+      image,
+      cmd
   end
 
   def start
@@ -33,17 +36,17 @@ class Mrsk::Commands::Accessory < Mrsk::Commands::Base
   end
 
 
-  def logs(since: nil, lines: nil, grep: nil)
+  def logs(since: nil, lines: nil, grep: nil, grep_options: nil)
     pipe \
-      docker(:logs, service_name, (" --since #{since}" if since), (" -n #{lines}" if lines), "-t", "2>&1"),
+      docker(:logs, service_name, (" --since #{since}" if since), (" --tail #{lines}" if lines), "--timestamps", "2>&1"),
-      ("grep '#{grep}'" if grep)
+      ("grep '#{grep}'#{" #{grep_options}" if grep_options}" if grep)
   end
 
-  def follow_logs(grep: nil)
+  def follow_logs(grep: nil, grep_options: nil)
     run_over_ssh \
       pipe \
-        docker(:logs, service_name, "-t", "-n", "10", "-f", "2>&1"),
+        docker(:logs, service_name, "--timestamps", "--tail", "10", "--follow", "2>&1"),
-        (%(grep "#{grep}") if grep)
+        (%(grep "#{grep}"#{" #{grep_options}" if grep_options}) if grep)
   end
 
 
@@ -73,7 +76,7 @@ class Mrsk::Commands::Accessory < Mrsk::Commands::Base
   end
 
   def run_over_ssh(command)
-    super command, host: host
+    super command, host: hosts.first
   end
 
 
@@ -83,24 +86,24 @@ class Mrsk::Commands::Accessory < Mrsk::Commands::Base
     end
   end
 
-  def make_directory_for(remote_file)
-    make_directory Pathname.new(remote_file).dirname.to_s
-  end
-
-  def make_directory(path)
-    [ :mkdir, "-p", path ]
-  end
-
   def remove_service_directory
     [ :rm, "-rf", service_name ]
   end
 
   def remove_container
-    docker :container, :prune, "-f", *service_filter
+    docker :container, :prune, "--force", *service_filter
   end
 
   def remove_image
-    docker :image, :prune, "-a", "-f", *service_filter
+    docker :image, :rm, "--force", image
+  end
+
+  def make_env_directory
+    make_directory accessory_config.env.secrets_directory
+  end
+
+  def remove_env_file
+    [ :rm, "-f", accessory_config.env.secrets_file ]
   end
 
   private

lib/kamal/commands/app.rb

@@ -0,0 +1,123 @@
+class Kamal::Commands::App < Kamal::Commands::Base
+  include Assets, Containers, Cord, Execution, Images, Logging
+
+  ACTIVE_DOCKER_STATUSES = [ :running, :restarting ]
+
+  attr_reader :role, :host
+
+  def initialize(config, role: nil, host: nil)
+    super(config)
+    @role = role
+    @host = host
+  end
+
+  def run(hostname: nil)
+    docker :run,
+      "--detach",
+      "--restart unless-stopped",
+      "--name", container_name,
+      *([ "--hostname", hostname ] if hostname),
+      "-e", "KAMAL_CONTAINER_NAME=\"#{container_name}\"",
+      "-e", "KAMAL_VERSION=\"#{config.version}\"",
+      *role.env_args(host),
+      *role.health_check_args,
+      *role.logging_args,
+      *config.volume_args,
+      *role.asset_volume_args,
+      *role.label_args,
+      *role.option_args,
+      config.absolute_image,
+      role.cmd
+  end
+
+  def start
+    docker :start, container_name
+  end
+
+  def status(version:)
+    pipe container_id_for_version(version), xargs(docker(:inspect, "--format", DOCKER_HEALTH_STATUS_FORMAT))
+  end
+
+  def stop(version: nil)
+    pipe \
+      version ? container_id_for_version(version) : current_running_container_id,
+      xargs(config.stop_wait_time ? docker(:stop, "-t", config.stop_wait_time) : docker(:stop))
+  end
+
+  def info
+    docker :ps, *filter_args
+  end
+
+
+  def current_running_container_id
+    current_running_container(format: "--quiet")
+  end
+
+  def container_id_for_version(version, only_running: false)
+    container_id_for(container_name: container_name(version), only_running: only_running)
+  end
+
+  def current_running_version
+    pipe \
+      current_running_container(format: "--format '{{.Names}}'"),
+      extract_version_from_name
+  end
+
+  def list_versions(*docker_args, statuses: nil)
+    pipe \
+      docker(:ps, *filter_args(statuses: statuses), *docker_args, "--format", '"{{.Names}}"'),
+      extract_version_from_name
+  end
+
+
+  def make_env_directory
+    make_directory role.env(host).secrets_directory
+  end
+
+  def remove_env_file
+    [ :rm, "-f", role.env(host).secrets_file ]
+  end
+
+
+  private
+    def container_name(version = nil)
+      [ role.container_prefix, version || config.version ].compact.join("-")
+    end
+
+    def latest_image_id
+      docker :image, :ls, *argumentize("--filter", "reference=#{config.latest_image}"), "--format", "'{{.ID}}'"
+    end
+
+    def current_running_container(format:)
+      pipe \
+        shell(chain(latest_image_container(format: format), latest_container(format: format))),
+        [ :head, "-1" ]
+    end
+
+    def latest_image_container(format:)
+      latest_container format: format, filters: [ "ancestor=$(#{latest_image_id.join(" ")})" ]
+    end
+
+    def latest_container(format:, filters: nil)
+      docker :ps, "--latest", *format, *filter_args(statuses: ACTIVE_DOCKER_STATUSES), argumentize("--filter", filters)
+    end
+
+    def filter_args(statuses: nil)
+      argumentize "--filter", filters(statuses: statuses)
+    end
+
+    def extract_version_from_name
+      # Extract SHA from "service-role-dest-SHA"
+      %(while read line; do echo ${line##{role.container_prefix}-}; done)
+    end
+
+    def filters(statuses: nil)
+      [ "label=service=#{config.service}" ].tap do |filters|
+        filters << "label=destination=#{config.destination}" if config.destination
+        filters << "label=role=#{role}" if role
+        statuses&.each do |status|
+          filters << "status=#{status}"
+        end
+      end
+    end
+end

lib/kamal/commands/app/assets.rb

@@ -0,0 +1,51 @@
+module Kamal::Commands::App::Assets
+  def extract_assets
+    asset_container = "#{role.container_prefix}-assets"
+
+    combine \
+      make_directory(role.asset_extracted_path),
+      [ *docker(:stop, "-t 1", asset_container, "2> /dev/null"), "|| true" ],
+      docker(:run, "--name", asset_container, "--detach", "--rm", config.absolute_image, "sleep 1000000"),
+      docker(:cp, "-L", "#{asset_container}:#{role.asset_path}/.", role.asset_extracted_path),
+      docker(:stop, "-t 1", asset_container),
+      by: "&&"
+  end
+
+  def sync_asset_volumes(old_version: nil)
+    new_extracted_path, new_volume_path = role.asset_extracted_path(config.version), role.asset_volume.host_path
+    if old_version.present?
+      old_extracted_path, old_volume_path = role.asset_extracted_path(old_version), role.asset_volume(old_version).host_path
+    end
+
+    commands = [ make_directory(new_volume_path), copy_contents(new_extracted_path, new_volume_path) ]
+
+    if old_version.present?
+      commands << copy_contents(new_extracted_path, old_volume_path, continue_on_error: true)
+      commands << copy_contents(old_extracted_path, new_volume_path, continue_on_error: true)
+    end
+
+    chain *commands
+  end
+
+  def clean_up_assets
+    chain \
+      find_and_remove_older_siblings(role.asset_extracted_path),
+      find_and_remove_older_siblings(role.asset_volume_path)
+  end
+
+  private
+    def find_and_remove_older_siblings(path)
+      [
+        :find,
+        Pathname.new(path).dirname.to_s,
+        "-maxdepth 1",
+        "-name", "'#{role.container_prefix}-*'",
+        "!", "-name", Pathname.new(path).basename.to_s,
+        "-exec rm -rf \"{}\" +"
+      ]
+    end
+
+    def copy_contents(source, destination, continue_on_error: false)
+      [ :cp, "-rnT", "#{source}", destination, *("|| true" if continue_on_error) ]
+    end
+end

lib/kamal/commands/app/containers.rb

@@ -0,0 +1,31 @@
+module Kamal::Commands::App::Containers
+  DOCKER_HEALTH_LOG_FORMAT    = "'{{json .State.Health}}'"
+
+  def list_containers
+    docker :container, :ls, "--all", *filter_args
+  end
+
+  def list_container_names
+    [ *list_containers, "--format", "'{{ .Names }}'" ]
+  end
+
+  def remove_container(version:)
+    pipe \
+      container_id_for(container_name: container_name(version)),
+      xargs(docker(:container, :rm))
+  end
+
+  def rename_container(version:, new_version:)
+    docker :rename, container_name(version), container_name(new_version)
+  end
+
+  def remove_containers
+    docker :container, :prune, "--force", *filter_args
+  end
+
+  def container_health_log(version:)
+    pipe \
+      container_id_for(container_name: container_name(version)),
+      xargs(docker(:inspect, "--format", DOCKER_HEALTH_LOG_FORMAT))
+  end
+end

lib/kamal/commands/app/cord.rb

@@ -0,0 +1,22 @@
+module Kamal::Commands::App::Cord
+  def cord(version:)
+    pipe \
+      docker(:inspect, "-f '{{ range .Mounts }}{{printf \"%s %s\\n\" .Source .Destination}}{{ end }}'", container_name(version)),
+      [ :awk, "'$2 == \"#{role.cord_volume.container_path}\" {print $1}'" ]
+  end
+
+  def tie_cord(cord)
+    create_empty_file(cord)
+  end
+
+  def cut_cord(cord)
+    remove_directory(cord)
+  end
+
+  private
+    def create_empty_file(file)
+      chain \
+        make_directory_for(file),
+        [ :touch, file ]
+    end
+end

lib/kamal/commands/app/execution.rb

@@ -0,0 +1,29 @@
+module Kamal::Commands::App::Execution
+  def execute_in_existing_container(*command, interactive: false, env:)
+    docker :exec,
+      ("-it" if interactive),
+      *argumentize("--env", env),
+      container_name,
+      *command
+  end
+
+  def execute_in_new_container(*command, interactive: false, env:)
+    docker :run,
+      ("-it" if interactive),
+      "--rm",
+      *role&.env_args(host),
+      *argumentize("--env", env),
+      *config.volume_args,
+      *role&.option_args,
+      config.absolute_image,
+      *command
+  end
+
+  def execute_in_existing_container_over_ssh(*command,  env:)
+    run_over_ssh execute_in_existing_container(*command, interactive: true, env: env), host: host
+  end
+
+  def execute_in_new_container_over_ssh(*command, env:)
+    run_over_ssh execute_in_new_container(*command, interactive: true, env: env), host: host
+  end
+end

lib/kamal/commands/app/images.rb

@@ -0,0 +1,13 @@
+module Kamal::Commands::App::Images
+  def list_images
+    docker :image, :ls, config.repository
+  end
+
+  def remove_images
+    docker :image, :prune, "--all", "--force", *filter_args
+  end
+
+  def tag_latest_image
+    docker :tag, config.absolute_image, config.latest_image
+  end
+end

lib/kamal/commands/app/logging.rb

@@ -0,0 +1,18 @@
+module Kamal::Commands::App::Logging
+  def logs(version: nil, since: nil, lines: nil, grep: nil, grep_options: nil)
+    pipe \
+      version ? container_id_for_version(version) : current_running_container_id,
+      "xargs docker logs#{" --since #{since}" if since}#{" --tail #{lines}" if lines} 2>&1",
+      ("grep '#{grep}'#{" #{grep_options}" if grep_options}" if grep)
+  end
+
+  def follow_logs(host:, lines: nil, grep: nil, grep_options: nil)
+    run_over_ssh \
+      pipe(
+        current_running_container_id,
+        "xargs docker logs --timestamps#{" --tail #{lines}" if lines} --follow 2>&1",
+        (%(grep "#{grep}"#{" #{grep_options}" if grep_options}) if grep)
+      ),
+      host: host
+  end
+end

lib/kamal/commands/auditor.rb

@@ -0,0 +1,30 @@
+class Kamal::Commands::Auditor < Kamal::Commands::Base
+  attr_reader :details
+
+  def initialize(config, **details)
+    super(config)
+    @details = details
+  end
+
+  # Runs remotely
+  def record(line, **details)
+    append \
+      [ :echo, audit_tags(**details).except(:version, :service_version, :service).to_s, line ],
+      audit_log_file
+  end
+
+  def reveal
+    [ :tail, "-n", 50, audit_log_file ]
+  end
+
+  private
+    def audit_log_file
+      file = [ config.service, config.destination, "audit.log" ].compact.join("-")
+
+      File.join(config.run_directory, file)
+    end
+
+    def audit_tags(**details)
+      tags(**self.details, **details)
+    end
+end

lib/kamal/commands/base.rb

@@ -0,0 +1,88 @@
+module Kamal::Commands
+  class Base
+    delegate :sensitive, :argumentize, to: Kamal::Utils
+
+    DOCKER_HEALTH_STATUS_FORMAT = "'{{if .State.Health}}{{.State.Health.Status}}{{else}}{{.State.Status}}{{end}}'"
+
+    attr_accessor :config
+
+    def initialize(config)
+      @config = config
+    end
+
+    def run_over_ssh(*command, host:)
+      "ssh".tap do |cmd|
+        if config.ssh.proxy && config.ssh.proxy.is_a?(Net::SSH::Proxy::Jump)
+          cmd << " -J #{config.ssh.proxy.jump_proxies}"
+        elsif config.ssh.proxy && config.ssh.proxy.is_a?(Net::SSH::Proxy::Command)
+          cmd << " -o ProxyCommand='#{config.ssh.proxy.command_line_template}'"
+        end
+        cmd << " -t #{config.ssh.user}@#{host} -p #{config.ssh.port} '#{command.join(" ").gsub("'", "'\\\\''")}'"
+      end
+    end
+
+    def container_id_for(container_name:, only_running: false)
+      docker :container, :ls, *("--all" unless only_running), "--filter", "name=^#{container_name}$", "--quiet"
+    end
+
+    def make_directory_for(remote_file)
+      make_directory Pathname.new(remote_file).dirname.to_s
+    end
+
+    def make_directory(path)
+      [ :mkdir, "-p", path ]
+    end
+
+    def remove_directory(path)
+      [ :rm, "-r", path ]
+    end
+
+    private
+      def combine(*commands, by: "&&")
+        commands
+          .compact
+          .collect { |command| Array(command) + [ by ] }.flatten # Join commands
+          .tap     { |commands| commands.pop } # Remove trailing combiner
+      end
+
+      def chain(*commands)
+        combine *commands, by: ";"
+      end
+
+      def pipe(*commands)
+        combine *commands, by: "|"
+      end
+
+      def append(*commands)
+        combine *commands, by: ">>"
+      end
+
+      def write(*commands)
+        combine *commands, by: ">"
+      end
+
+      def any(*commands)
+        combine *commands, by: "||"
+      end
+
+      def xargs(command)
+        [ :xargs, command ].flatten
+      end
+
+      def shell(command)
+        [ :sh, "-c", "'#{command.flatten.join(" ").gsub("'", "'\\\\''")}'" ]
+      end
+
+      def docker(*args)
+        args.compact.unshift :docker
+      end
+
+      def git(*args, path: nil)
+        [ :git, *([ "-C", path ] if path), *args.compact ]
+      end
+
+      def tags(**details)
+        Kamal::Tags.from_config(config, **details)
+      end
+  end
+end

lib/kamal/commands/builder.rb

@@ -0,0 +1,72 @@
+require "active_support/core_ext/string/filters"
+
+class Kamal::Commands::Builder < Kamal::Commands::Base
+  delegate :create, :remove, :push, :clean, :pull, :info, :context_hosts, :config_context_hosts, :validate_image,
+           :first_mirror, to: :target
+
+  include Clone
+
+  def name
+    target.class.to_s.remove("Kamal::Commands::Builder::").underscore.inquiry
+  end
+
+  def target
+    if config.builder.multiarch?
+      if config.builder.remote?
+        if config.builder.local?
+          multiarch_remote
+        else
+          native_remote
+        end
+      else
+        multiarch
+      end
+    else
+      if config.builder.cached?
+        native_cached
+      else
+        native
+      end
+    end
+  end
+
+  def native
+    @native ||= Kamal::Commands::Builder::Native.new(config)
+  end
+
+  def native_cached
+    @native ||= Kamal::Commands::Builder::Native::Cached.new(config)
+  end
+
+  def native_remote
+    @native ||= Kamal::Commands::Builder::Native::Remote.new(config)
+  end
+
+  def multiarch
+    @multiarch ||= Kamal::Commands::Builder::Multiarch.new(config)
+  end
+
+  def multiarch_remote
+    @multiarch_remote ||= Kamal::Commands::Builder::Multiarch::Remote.new(config)
+  end
+
+
+  def ensure_local_dependencies_installed
+    if name.native?
+      ensure_local_docker_installed
+    else
+      combine \
+        ensure_local_docker_installed,
+        ensure_local_buildx_installed
+    end
+  end
+
+  private
+    def ensure_local_docker_installed
+      docker "--version"
+    end
+
+    def ensure_local_buildx_installed
+      docker :buildx, "version"
+    end
+end

lib/kamal/commands/builder/base.rb

@@ -0,0 +1,94 @@
+
+class Kamal::Commands::Builder::Base < Kamal::Commands::Base
+  class BuilderError < StandardError; end
+
+  ENDPOINT_DOCKER_HOST_INSPECT = "'{{.Endpoints.docker.Host}}'"
+
+  delegate :argumentize, to: Kamal::Utils
+  delegate :args, :secrets, :dockerfile, :target, :local_arch, :local_host, :remote_arch, :remote_host, :cache_from, :cache_to, :ssh, to: :builder_config
+
+  def clean
+    docker :image, :rm, "--force", config.absolute_image
+  end
+
+  def pull
+    docker :pull, config.absolute_image
+  end
+
+  def build_options
+    [ *build_tags, *build_cache, *build_labels, *build_args, *build_secrets, *build_dockerfile, *build_target, *build_ssh ]
+  end
+
+  def build_context
+    config.builder.context
+  end
+
+  def validate_image
+    pipe \
+      docker(:inspect, "-f", "'{{ .Config.Labels.service }}'", config.absolute_image),
+      any(
+        [ :grep, "-x", config.service ],
+        "(echo \"Image #{config.absolute_image} is missing the 'service' label\" && exit 1)"
+      )
+  end
+
+  def context_hosts
+    :true
+  end
+
+  def config_context_hosts
+    []
+  end
+
+  def first_mirror
+    docker(:info, "--format '{{index .RegistryConfig.Mirrors 0}}'")
+  end
+
+  private
+    def build_tags
+      [ "-t", config.absolute_image, "-t", config.latest_image ]
+    end
+
+    def build_cache
+      if cache_to && cache_from
+        [ "--cache-to", cache_to,
+          "--cache-from", cache_from ]
+      end
+    end
+
+    def build_labels
+      argumentize "--label", { service: config.service }
+    end
+
+    def build_args
+      argumentize "--build-arg", args, sensitive: true
+    end
+
+    def build_secrets
+      argumentize "--secret", secrets.collect { |secret| [ "id", secret ] }
+    end
+
+    def build_dockerfile
+      if Pathname.new(File.expand_path(dockerfile)).exist?
+        argumentize "--file", dockerfile
+      else
+        raise BuilderError, "Missing #{dockerfile}"
+      end
+    end
+
+    def build_target
+      argumentize "--target", target if target.present?
+    end
+
+    def build_ssh
+      argumentize "--ssh", ssh if ssh.present?
+    end
+
+    def builder_config
+      config.builder
+    end
+
+    def context_host(builder_name)
+      docker :context, :inspect, builder_name, "--format", ENDPOINT_DOCKER_HOST_INSPECT
+    end
+end

lib/kamal/commands/builder/clone.rb

@@ -0,0 +1,28 @@
+module Kamal::Commands::Builder::Clone
+  extend ActiveSupport::Concern
+
+  included do
+    delegate :clone_directory, :build_directory, to: :"config.builder"
+  end
+
+  def clone
+    git :clone, Kamal::Git.root, path: clone_directory
+  end
+
+  def clone_reset_steps
+    [
+      git(:remote, "set-url", :origin, Kamal::Git.root, path: build_directory),
+      git(:fetch, :origin, path: build_directory),
+      git(:reset, "--hard", Kamal::Git.revision, path: build_directory),
+      git(:clean, "-fdx", path: build_directory)
+    ]
+  end
+
+  def clone_status
+    git :status, "--porcelain", path: build_directory
+  end
+
+  def clone_revision
+    git :"rev-parse", :HEAD, path: build_directory
+  end
+end

lib/kamal/commands/builder/multiarch.rb

@@ -0,0 +1,41 @@
+class Kamal::Commands::Builder::Multiarch < Kamal::Commands::Builder::Base
+  def create
+    docker :buildx, :create, "--use", "--name", builder_name
+  end
+
+  def remove
+    docker :buildx, :rm, builder_name
+  end
+
+  def info
+    combine \
+      docker(:context, :ls),
+      docker(:buildx, :ls)
+  end
+
+  def push
+    docker :buildx, :build,
+      "--push",
+      "--platform", platform_names,
+      "--builder", builder_name,
+      *build_options,
+      build_context
+  end
+
+  def context_hosts
+    docker :buildx, :inspect, builder_name, "> /dev/null"
+  end
+
+  private
+    def builder_name
+      "kamal-#{config.service}-multiarch"
+    end
+
+    def platform_names
+      if local_arch
+        "linux/#{local_arch}"
+      else
+        "linux/amd64,linux/arm64"
+      end
+    end
+end

lib/kamal/commands/builder/multiarch/remote.rb

@@ -1,4 +1,4 @@
-class Mrsk::Commands::Builder::Multiarch::Remote < Mrsk::Commands::Builder::Multiarch
+class Kamal::Commands::Builder::Multiarch::Remote < Kamal::Commands::Builder::Multiarch
   def create
     combine \
       create_contexts,
@@ -12,6 +12,16 @@ class Mrsk::Commands::Builder::Multiarch::Remote < Mrsk::Commands::Builder::Mult
       super
   end
 
+  def context_hosts
+    chain \
+      context_host(builder_name_with_arch(local_arch)),
+      context_host(builder_name_with_arch(remote_arch))
+  end
+
+  def config_context_hosts
+    [ local_host, remote_host ].compact
+  end
+
   private
     def builder_name
       super + "-remote"
@@ -22,17 +32,17 @@ class Mrsk::Commands::Builder::Multiarch::Remote < Mrsk::Commands::Builder::Mult
     end
 
     def create_local_buildx
-      docker :buildx, :create, "--name", builder_name, builder_name_with_arch(local["arch"]), "--platform", "linux/#{local["arch"]}"
+      docker :buildx, :create, "--name", builder_name, builder_name_with_arch(local_arch), "--platform", "linux/#{local_arch}"
     end
 
     def append_remote_buildx
-      docker :buildx, :create, "--append", "--name", builder_name, builder_name_with_arch(remote["arch"]), "--platform", "linux/#{remote["arch"]}"
+      docker :buildx, :create, "--append", "--name", builder_name, builder_name_with_arch(remote_arch), "--platform", "linux/#{remote_arch}"
     end
 
     def create_contexts
       combine \
-        create_context(local["arch"], local["host"]),
+        create_context(local_arch, local_host),
-        create_context(remote["arch"], remote["host"])
+        create_context(remote_arch, remote_host)
     end
 
     def create_context(arch, host)
@@ -41,19 +51,11 @@ class Mrsk::Commands::Builder::Multiarch::Remote < Mrsk::Commands::Builder::Mult
 
     def remove_contexts
       combine \
-        remove_context(local["arch"]),
+        remove_context(local_arch),
-        remove_context(remote["arch"])
+        remove_context(remote_arch)
     end
 
     def remove_context(arch)
       docker :context, :rm, builder_name_with_arch(arch)
     end
-
-    def local
-      config.builder["local"]
-    end
-
-    def remote
-      config.builder["remote"]
-    end
 end

lib/kamal/commands/builder/native.rb

@@ -0,0 +1,20 @@
+class Kamal::Commands::Builder::Native < Kamal::Commands::Builder::Base
+  def create
+    # No-op on native without cache
+  end
+
+  def remove
+    # No-op on native without cache
+  end
+
+  def info
+    # No-op on native
+  end
+
+  def push
+    combine \
+      docker(:build, *build_options, build_context),
+      docker(:push, config.absolute_image),
+      docker(:push, config.latest_image)
+  end
+end

lib/kamal/commands/builder/native/cached.rb

@@ -0,0 +1,25 @@
+class Kamal::Commands::Builder::Native::Cached < Kamal::Commands::Builder::Native
+  def create
+    docker :buildx, :create, "--name", builder_name, "--use", "--driver=docker-container"
+  end
+
+  def remove
+    docker :buildx, :rm, builder_name
+  end
+
+  def push
+    docker :buildx, :build,
+      "--push",
+      *build_options,
+      build_context
+  end
+
+  def context_hosts
+    docker :buildx, :inspect, builder_name, "> /dev/null"
+  end
+
+  private
+    def builder_name
+      "kamal-#{config.service}-native-cached"
+    end
+end

lib/kamal/commands/builder/native/remote.rb

@@ -1,4 +1,4 @@
-class Mrsk::Commands::Builder::Native::Remote < Mrsk::Commands::Builder::Native
+class Kamal::Commands::Builder::Native::Remote < Kamal::Commands::Builder::Native
   def create
     chain \
       create_context,
@@ -11,48 +11,46 @@ class Mrsk::Commands::Builder::Native::Remote < Mrsk::Commands::Builder::Native
       remove_buildx
   end
 
-  def push
-    docker :buildx, :build,
-      "--push",
-      "--platform", platform,
-      "--builder", builder_name,
-      *build_tags,
-      *build_args,
-      *build_secrets,
-      "."
-  end
-
   def info
     chain \
       docker(:context, :ls),
       docker(:buildx, :ls)
   end
 
+  def push
+    docker :buildx, :build,
+    "--push",
+    "--platform", platform,
+    "--builder", builder_name,
+    *build_options,
+    build_context
+  end
+
+  def context_hosts
+    context_host(builder_name_with_arch)
+  end
+
+  def config_context_hosts
+    [ remote_host ]
+  end
+
 
   private
-    def arch
-      config.builder["remote"]["arch"]
-    end
-
-    def host
-      config.builder["remote"]["host"]
-    end
-
     def builder_name
-      "mrsk-#{config.service}-native-remote"
+      "kamal-#{config.service}-native-remote"
     end
 
     def builder_name_with_arch
-      "#{builder_name}-#{arch}"
+      "#{builder_name}-#{remote_arch}"
     end
 
     def platform
-      "linux/#{arch}"
+      "linux/#{remote_arch}"
     end
 
     def create_context
       docker :context, :create,
-        builder_name_with_arch, "--description", "'#{builder_name} #{arch} native host'", "--docker", "'host=#{host}'"
+        builder_name_with_arch, "--description", "'#{builder_name} #{remote_arch} native host'", "--docker", "'host=#{remote_host}'"
     end
 
     def remove_context

lib/kamal/commands/docker.rb

@@ -0,0 +1,30 @@
+class Kamal::Commands::Docker < Kamal::Commands::Base
+  # Install Docker using the https://github.com/docker/docker-install convenience script.
+  def install
+    pipe get_docker, :sh
+  end
+
+  # Checks the Docker client version. Fails if Docker is not installed.
+  def installed?
+    docker "-v"
+  end
+
+  # Checks the Docker server version. Fails if Docker is not running.
+  def running?
+    docker :version
+  end
+
+  # Do we have superuser access to install Docker and start system services?
+  def superuser?
+    [ '[ "${EUID:-$(id -u)}" -eq 0 ] || command -v sudo >/dev/null || command -v su >/dev/null' ]
+  end
+
+  private
+    def get_docker
+      shell \
+        any \
+          [ :curl, "-fsSL", "https://get.docker.com" ],
+          [ :wget, "-O -", "https://get.docker.com" ],
+          [ :echo, "\"exit 1\"" ]
+    end
+end

lib/kamal/commands/hook.rb

@@ -0,0 +1,5 @@
+class Kamal::Commands::Hook < Kamal::Commands::Base
+  def run(hook, **details)
+    [ Kamal::Hooks.file(hook), env: tags(**details).env ]
+  end
+end

lib/kamal/commands/lock.rb

@@ -0,0 +1,74 @@
+require "active_support/duration"
+require "time"
+require "base64"
+
+class Kamal::Commands::Lock < Kamal::Commands::Base
+  def acquire(message, version)
+    combine \
+      [ :mkdir, lock_dir ],
+      write_lock_details(message, version)
+  end
+
+  def release
+    combine \
+      [ :rm, lock_details_file ],
+      [ :rm, "-r", lock_dir ]
+  end
+
+  def status
+    combine \
+      stat_lock_dir,
+      read_lock_details
+  end
+
+  def ensure_locks_directory
+    [ :mkdir, "-p", locks_dir ]
+  end
+
+  private
+    def write_lock_details(message, version)
+      write \
+        [ :echo, "\"#{Base64.encode64(lock_details(message, version))}\"" ],
+        lock_details_file
+    end
+
+    def read_lock_details
+      pipe \
+        [ :cat, lock_details_file ],
+        [ :base64, "-d" ]
+    end
+
+    def stat_lock_dir
+      write \
+        [ :stat, lock_dir ],
+        "/dev/null"
+    end
+
+    def locks_dir
+      File.join(config.run_directory, "locks")
+    end
+
+    def lock_dir
+      dir_name = [ config.service, config.destination ].compact.join("-")
+
+      File.join(locks_dir, dir_name)
+    end
+
+    def lock_details_file
+      File.join(lock_dir, "details")
+    end
+
+    def lock_details(message, version)
+      <<~DETAILS.strip
+        Locked by: #{locked_by} at #{Time.now.utc.iso8601}
+        Version: #{version}
+        Message: #{message}
+      DETAILS
+    end
+
+    def locked_by
+      Kamal::Git.user_name
+    rescue Errno::ENOENT
+      "Unknown"
+    end
+end

lib/kamal/commands/prune.rb

@@ -0,0 +1,46 @@
+require "active_support/duration"
+require "active_support/core_ext/numeric/time"
+
+class Kamal::Commands::Prune < Kamal::Commands::Base
+  def dangling_images
+    docker :image, :prune, "--force", "--filter", "label=service=#{config.service}"
+  end
+
+  def tagged_images
+    pipe \
+      docker(:image, :ls, *service_filter, "--format", "'{{.ID}} {{.Repository}}:{{.Tag}}'"),
+      "grep -v -w \"#{active_image_list}\"",
+      "while read image tag; do docker rmi $tag; done"
+  end
+
+  def app_containers(retain:)
+    pipe \
+      docker(:ps, "-q", "-a", *service_filter, *stopped_containers_filters),
+      "tail -n +#{retain + 1}",
+      "while read container_id; do docker rm $container_id; done"
+  end
+
+  def healthcheck_containers
+    docker :container, :prune, "--force", *healthcheck_service_filter
+  end
+
+  private
+    def stopped_containers_filters
+      [ "created", "exited", "dead" ].flat_map { |status| [ "--filter", "status=#{status}" ] }
+    end
+
+    def active_image_list
+      # Pull the images that are used by any containers
+      # Append repo:latest - to avoid deleting the latest tag
+      # Append repo:<none> - to avoid deleting dangling images that are in use. Unused dangling images are deleted separately
+      "$(docker container ls -a --format '{{.Image}}\\|' --filter label=service=#{config.service} | tr -d '\\n')#{config.latest_image}\\|#{config.repository}:<none>"
+    end
+
+    def service_filter
+      [ "--filter", "label=service=#{config.service}" ]
+    end
+
+    def healthcheck_service_filter
+      [ "--filter", "label=service=#{config.healthcheck_service}" ]
+    end
+end

lib/kamal/commands/registry.rb

@@ -0,0 +1,14 @@
+class Kamal::Commands::Registry < Kamal::Commands::Base
+  delegate :registry, to: :config
+
+  def login
+    docker :login,
+      registry.server,
+      "-u", sensitive(Kamal::Utils.escape_shell_value(registry.username)),
+      "-p", sensitive(Kamal::Utils.escape_shell_value(registry.password))
+  end
+
+  def logout
+    docker :logout, registry.server
+  end
+end

lib/kamal/commands/server.rb

@@ -0,0 +1,5 @@
+class Kamal::Commands::Server < Kamal::Commands::Base
+  def ensure_run_directory
+    [ :mkdir, "-p", config.run_directory ]
+  end
+end

lib/kamal/commands/traefik.rb

@@ -0,0 +1,85 @@
+class Kamal::Commands::Traefik < Kamal::Commands::Base
+  delegate :argumentize, :optionize, to: Kamal::Utils
+  delegate :port, :publish?, :labels, :env, :image, :options, :args, to: :"config.traefik"
+
+  def run
+    docker :run, "--name traefik",
+      "--detach",
+      "--restart", "unless-stopped",
+      *publish_args,
+      "--volume", "/var/run/docker.sock:/var/run/docker.sock",
+      *env_args,
+      *config.logging_args,
+      *label_args,
+      *docker_options_args,
+      image,
+      "--providers.docker",
+      *cmd_option_args
+  end
+
+  def start
+    docker :container, :start, "traefik"
+  end
+
+  def stop
+    docker :container, :stop, "traefik"
+  end
+
+  def start_or_run
+    any start, run
+  end
+
+  def info
+    docker :ps, "--filter", "name=^traefik$"
+  end
+
+  def logs(since: nil, lines: nil, grep: nil, grep_options: nil)
+    pipe \
+      docker(:logs, "traefik", (" --since #{since}" if since), (" --tail #{lines}" if lines), "--timestamps", "2>&1"),
+      ("grep '#{grep}'#{" #{grep_options}" if grep_options}" if grep)
+  end
+
+  def follow_logs(host:, grep: nil, grep_options: nil)
+    run_over_ssh pipe(
+      docker(:logs, "traefik", "--timestamps", "--tail", "10", "--follow", "2>&1"),
+      (%(grep "#{grep}"#{" #{grep_options}" if grep_options}) if grep)
+    ).join(" "), host: host
+  end
+
+  def remove_container
+    docker :container, :prune, "--force", "--filter", "label=org.opencontainers.image.title=Traefik"
+  end
+
+  def remove_image
+    docker :image, :prune, "--all", "--force", "--filter", "label=org.opencontainers.image.title=Traefik"
+  end
+
+  def make_env_directory
+    make_directory(env.secrets_directory)
+  end
+
+  def remove_env_file
+    [ :rm, "-f", env.secrets_file ]
+  end
+
+  private
+    def publish_args
+      argumentize "--publish", port if publish?
+    end
+
+    def label_args
+      argumentize "--label", labels
+    end
+
+    def env_args
+      env.args
+    end
+
+    def docker_options_args
+      optionize(options)
+    end
+
+    def cmd_option_args
+      optionize args, with: "="
+    end
+end

lib/kamal/configuration.rb

@@ -0,0 +1,322 @@
+require "active_support/ordered_options"
+require "active_support/core_ext/string/inquiry"
+require "active_support/core_ext/module/delegation"
+require "active_support/core_ext/hash/keys"
+require "pathname"
+require "erb"
+require "net/ssh/proxy/jump"
+
+class Kamal::Configuration
+  delegate :service, :image, :labels, :stop_wait_time, to: :raw_config, allow_nil: true
+  delegate :argumentize, :optionize, to: Kamal::Utils
+
+  attr_reader :destination, :raw_config
+  attr_reader :accessories, :boot, :builder, :env, :healthcheck, :logging, :traefik, :servers, :ssh, :sshkit, :registry
+
+  include Validation
+
+  class << self
+    def create_from(config_file:, destination: nil, version: nil)
+      raw_config = load_config_files(config_file, *destination_config_file(config_file, destination))
+
+      new raw_config, destination: destination, version: version
+    end
+
+    private
+      def load_config_files(*files)
+        files.inject({}) { |config, file| config.deep_merge! load_config_file(file) }
+      end
+
+      def load_config_file(file)
+        if file.exist?
+          # Newer Psych doesn't load aliases by default
+          load_method = YAML.respond_to?(:unsafe_load) ? :unsafe_load : :load
+          YAML.send(load_method, ERB.new(IO.read(file)).result).symbolize_keys
+        else
+          raise "Configuration file not found in #{file}"
+        end
+      end
+
+      def destination_config_file(base_config_file, destination)
+        base_config_file.sub_ext(".#{destination}.yml") if destination
+      end
+  end
+
+  def initialize(raw_config, destination: nil, version: nil, validate: true)
+    @raw_config = ActiveSupport::InheritableOptions.new(raw_config)
+    @destination = destination
+    @declared_version = version
+
+    validate! raw_config, example: validation_yml.symbolize_keys, context: "", with: Kamal::Configuration::Validator::Configuration
+
+    # Eager load config to validate it, these are first as they have dependencies later on
+    @servers = Servers.new(config: self)
+    @registry = Registry.new(config: self)
+
+    @accessories = @raw_config.accessories&.keys&.collect { |name| Accessory.new(name, config: self) } || []
+    @boot = Boot.new(config: self)
+    @builder = Builder.new(config: self)
+    @env = Env.new(config: @raw_config.env || {})
+
+    @healthcheck = Healthcheck.new(healthcheck_config: @raw_config.healthcheck)
+    @logging = Logging.new(logging_config: @raw_config.logging)
+    @traefik = Traefik.new(config: self)
+    @ssh = Ssh.new(config: self)
+    @sshkit = Sshkit.new(config: self)
+
+    ensure_destination_if_required
+    ensure_required_keys_present
+    ensure_valid_kamal_version
+    ensure_retain_containers_valid
+    ensure_valid_service_name
+  end
+
+
+  def version=(version)
+    @declared_version = version
+  end
+
+  def version
+    @declared_version.presence || ENV["VERSION"] || git_version
+  end
+
+  def abbreviated_version
+    if version
+      # Don't abbreviate <sha>_uncommitted_<etc>
+      if version.include?("_")
+        version
+      else
+        version[0...7]
+      end
+    end
+  end
+
+  def minimum_version
+    raw_config.minimum_version
+  end
+
+
+  def roles
+    servers.roles
+  end
+
+  def role(name)
+    roles.detect { |r| r.name == name.to_s }
+  end
+
+  def accessory(name)
+    accessories.detect { |a| a.name == name.to_s }
+  end
+
+
+  def all_hosts
+    (roles + accessories).flat_map(&:hosts).uniq
+  end
+
+  def primary_host
+    primary_role&.primary_host
+  end
+
+  def primary_role_name
+    raw_config.primary_role || "web"
+  end
+
+  def primary_role
+    role(primary_role_name)
+  end
+
+  def allow_empty_roles?
+    raw_config.allow_empty_roles
+  end
+
+  def traefik_roles
+    roles.select(&:running_traefik?)
+  end
+
+  def traefik_role_names
+    traefik_roles.flat_map(&:name)
+  end
+
+  def traefik_hosts
+    traefik_roles.flat_map(&:hosts).uniq
+  end
+
+  def repository
+    [ registry.server, image ].compact.join("/")
+  end
+
+  def absolute_image
+    "#{repository}:#{version}"
+  end
+
+  def latest_image
+    "#{repository}:#{latest_tag}"
+  end
+
+  def latest_tag
+    [ "latest", *destination ].join("-")
+  end
+
+  def service_with_version
+    "#{service}-#{version}"
+  end
+
+  def require_destination?
+    raw_config.require_destination
+  end
+
+  def retain_containers
+    raw_config.retain_containers || 5
+  end
+
+
+  def volume_args
+    if raw_config.volumes.present?
+      argumentize "--volume", raw_config.volumes
+    else
+      []
+    end
+  end
+
+  def logging_args
+    logging.args
+  end
+
+
+  def healthcheck_service
+    [ "healthcheck", service, destination ].compact.join("-")
+  end
+
+  def readiness_delay
+    raw_config.readiness_delay || 7
+  end
+
+  def run_id
+    @run_id ||= SecureRandom.hex(16)
+  end
+
+
+  def run_directory
+    raw_config.run_directory || ".kamal"
+  end
+
+  def run_directory_as_docker_volume
+    if Pathname.new(run_directory).absolute?
+      run_directory
+    else
+      File.join "$(pwd)", run_directory
+    end
+  end
+
+  def asset_path
+    raw_config.asset_path
+  end
+
+
+  def host_env_directory
+    File.join(run_directory, "env")
+  end
+
+  def env_tags
+    @env_tags ||= if (tags = raw_config.env["tags"])
+      tags.collect { |name, config| Env::Tag.new(name, config: config) }
+    else
+      []
+    end
+  end
+
+  def env_tag(name)
+    env_tags.detect { |t| t.name == name.to_s }
+  end
+
+
+  def to_h
+    {
+      roles: role_names,
+      hosts: all_hosts,
+      primary_host: primary_host,
+      version: version,
+      repository: repository,
+      absolute_image: absolute_image,
+      service_with_version: service_with_version,
+      volume_args: volume_args,
+      ssh_options: ssh.to_h,
+      sshkit: sshkit.to_h,
+      builder: builder.to_h,
+      accessories: raw_config.accessories,
+      logging: logging_args,
+      healthcheck: healthcheck.to_h
+    }.compact
+  end
+
+  private
+    # Will raise ArgumentError if any required config keys are missing
+    def ensure_destination_if_required
+      if require_destination? && destination.nil?
+        raise ArgumentError, "You must specify a destination"
+      end
+
+      true
+    end
+
+    def ensure_required_keys_present
+      %i[ service image registry servers ].each do |key|
+        raise Kamal::ConfigurationError, "Missing required configuration for #{key}" unless raw_config[key].present?
+      end
+
+      unless role(primary_role_name).present?
+        raise Kamal::ConfigurationError, "The primary_role #{primary_role_name} isn't defined"
+      end
+
+      if primary_role.hosts.empty?
+        raise Kamal::ConfigurationError, "No servers specified for the #{primary_role.name} primary_role"
+      end
+
+      unless allow_empty_roles?
+        roles.each do |role|
+          if role.hosts.empty?
+            raise Kamal::ConfigurationError, "No servers specified for the #{role.name} role. You can ignore this with allow_empty_roles: true"
+          end
+        end
+      end
+
+      true
+    end
+
+    def ensure_valid_service_name
+      raise Kamal::ConfigurationError, "Service name can only include alphanumeric characters, hyphens, and underscores" unless raw_config[:service] =~ /^[a-z0-9_-]+$/i
+
+      true
+    end
+
+    def ensure_valid_kamal_version
+      if minimum_version && Gem::Version.new(minimum_version) > Gem::Version.new(Kamal::VERSION)
+        raise Kamal::ConfigurationError, "Current version is #{Kamal::VERSION}, minimum required is #{minimum_version}"
+      end
+
+      true
+    end
+
+    def ensure_retain_containers_valid
+      raise Kamal::ConfigurationError, "Must retain at least 1 container" if retain_containers < 1
+
+      true
+    end
+
+
+    def role_names
+      raw_config.servers.is_a?(Array) ? [ "web" ] : raw_config.servers.keys.sort
+    end
+
+    def git_version
+      @git_version ||=
+        if Kamal::Git.used?
+          if Kamal::Git.uncommitted_changes.present? && !builder.git_clone?
+            uncommitted_suffix = "_uncommitted_#{SecureRandom.hex(8)}"
+          end
+          [ Kamal::Git.revision, uncommitted_suffix ].compact.join
+        else
+          raise "Can't use commit hash as version, no git repository found in #{Dir.pwd}"
+        end
+    end
+end

lib/kamal/configuration/accessory.rb

@@ -0,0 +1,164 @@
+class Kamal::Configuration::Accessory
+  include Kamal::Configuration::Validation
+
+  delegate :argumentize, :optionize, to: Kamal::Utils
+
+  attr_reader :name, :accessory_config, :env
+
+  def initialize(name, config:)
+    @name, @config, @accessory_config = name.inquiry, config, config.raw_config["accessories"][name]
+
+    validate! \
+      accessory_config,
+      example: validation_yml["accessories"]["mysql"],
+      context: "accessories/#{name}",
+      with: Kamal::Configuration::Validator::Accessory
+
+    @env = Kamal::Configuration::Env.new \
+      config: accessory_config.fetch("env", {}),
+      secrets_file: File.join(config.host_env_directory, "accessories", "#{service_name}.env"),
+      context: "accessories/#{name}/env"
+  end
+
+  def service_name
+    accessory_config["service"] || "#{config.service}-#{name}"
+  end
+
+  def image
+    accessory_config["image"]
+  end
+
+  def hosts
+    hosts_from_host || hosts_from_hosts || hosts_from_roles
+  end
+
+  def port
+    if port = accessory_config["port"]&.to_s
+      port.include?(":") ? port : "#{port}:#{port}"
+    end
+  end
+
+  def publish_args
+    argumentize "--publish", port if port
+  end
+
+  def labels
+    default_labels.merge(accessory_config["labels"] || {})
+  end
+
+  def label_args
+    argumentize "--label", labels
+  end
+
+  def env_args
+    env.args
+  end
+
+  def files
+    accessory_config["files"]&.to_h do |local_to_remote_mapping|
+      local_file, remote_file = local_to_remote_mapping.split(":")
+      [ expand_local_file(local_file), expand_remote_file(remote_file) ]
+    end || {}
+  end
+
+  def directories
+    accessory_config["directories"]&.to_h do |host_to_container_mapping|
+      host_path, container_path = host_to_container_mapping.split(":")
+      [ expand_host_path(host_path), container_path ]
+    end || {}
+  end
+
+  def volumes
+    specific_volumes + remote_files_as_volumes + remote_directories_as_volumes
+  end
+
+  def volume_args
+    argumentize "--volume", volumes
+  end
+
+  def option_args
+    if args = accessory_config["options"]
+      optionize args
+    else
+      []
+    end
+  end
+
+  def cmd
+    accessory_config["cmd"]
+  end
+
+  private
+    attr_accessor :config
+
+    def default_labels
+      { "service" => service_name }
+    end
+
+    def expand_local_file(local_file)
+      if local_file.end_with?("erb")
+        with_clear_env_loaded { read_dynamic_file(local_file) }
+      else
+        Pathname.new(File.expand_path(local_file)).to_s
+      end
+    end
+
+    def with_clear_env_loaded
+      env.clear.each { |k, v| ENV[k] = v }
+      yield
+    ensure
+      env.clear.each { |k, v| ENV.delete(k) }
+    end
+
+    def read_dynamic_file(local_file)
+      StringIO.new(ERB.new(IO.read(local_file)).result)
+    end
+
+    def expand_remote_file(remote_file)
+      service_name + remote_file
+    end
+
+    def specific_volumes
+      accessory_config["volumes"] || []
+    end
+
+    def remote_files_as_volumes
+      accessory_config["files"]&.collect do |local_to_remote_mapping|
+        _, remote_file = local_to_remote_mapping.split(":")
+        "#{service_data_directory + remote_file}:#{remote_file}"
+      end || []
+    end
+
+    def remote_directories_as_volumes
+      accessory_config["directories"]&.collect do |host_to_container_mapping|
+        host_path, container_path = host_to_container_mapping.split(":")
+        [ expand_host_path(host_path), container_path ].join(":")
+      end || []
+    end
+
+    def expand_host_path(host_path)
+      absolute_path?(host_path) ? host_path : File.join(service_data_directory, host_path)
+    end
+
+    def absolute_path?(path)
+      Pathname.new(path).absolute?
+    end
+
+    def service_data_directory
+      "$PWD/#{service_name}"
+    end
+
+    def hosts_from_host
+      [ accessory_config["host"] ] if accessory_config.key?("host")
+    end
+
+    def hosts_from_hosts
+      accessory_config["hosts"] if accessory_config.key?("hosts")
+    end
+
+    def hosts_from_roles
+      if accessory_config.key?("roles")
+        accessory_config["roles"].flat_map { |role| config.role(role).hosts }
+      end
+    end
+end

lib/kamal/configuration/boot.rb

@@ -0,0 +1,25 @@
+class Kamal::Configuration::Boot
+  include Kamal::Configuration::Validation
+
+  attr_reader :boot_config, :host_count
+
+  def initialize(config:)
+    @boot_config = config.raw_config.boot || {}
+    @host_count = config.all_hosts.count
+    validate! boot_config
+  end
+
+  def limit
+    limit = boot_config["limit"]
+
+    if limit.to_s.end_with?("%")
+      [ host_count * limit.to_i / 100, 1 ].max
+    else
+      limit
+    end
+  end
+
+  def wait
+    boot_config["wait"]
+  end
+end

lib/kamal/configuration/builder.rb

@@ -0,0 +1,153 @@
+class Kamal::Configuration::Builder
+  include Kamal::Configuration::Validation
+
+  attr_reader :config, :builder_config
+  delegate :image, :service, to: :config
+  delegate :server, to: :"config.registry"
+
+  def initialize(config:)
+    @config = config
+    @builder_config = config.raw_config.builder || {}
+    @image = config.image
+    @server = config.registry.server
+    @service = config.service
+
+    validate! builder_config, with: Kamal::Configuration::Validator::Builder
+  end
+
+  def to_h
+    builder_config
+  end
+
+  def multiarch?
+    builder_config["multiarch"] != false
+  end
+
+  def local?
+    !!builder_config["local"]
+  end
+
+  def remote?
+    !!builder_config["remote"]
+  end
+
+  def cached?
+    !!builder_config["cache"]
+  end
+
+  def args
+    builder_config["args"] || {}
+  end
+
+  def secrets
+    builder_config["secrets"] || []
+  end
+
+  def dockerfile
+    builder_config["dockerfile"] || "Dockerfile"
+  end
+
+  def target
+    builder_config["target"]
+  end
+
+  def context
+    builder_config["context"] || "."
+  end
+
+  def local_arch
+    builder_config["local"]["arch"] if local?
+  end
+
+  def local_host
+    builder_config["local"]["host"] if local?
+  end
+
+  def remote_arch
+    builder_config["remote"]["arch"] if remote?
+  end
+
+  def remote_host
+    builder_config["remote"]["host"] if remote?
+  end
+
+  def cache_from
+    if cached?
+      case builder_config["cache"]["type"]
+      when "gha"
+        cache_from_config_for_gha
+      when "registry"
+        cache_from_config_for_registry
+      end
+    end
+  end
+
+  def cache_to
+    if cached?
+      case builder_config["cache"]["type"]
+      when "gha"
+        cache_to_config_for_gha
+      when "registry"
+        cache_to_config_for_registry
+      end
+    end
+  end
+
+  def ssh
+    builder_config["ssh"]
+  end
+
+  def git_clone?
+    Kamal::Git.used? && builder_config["context"].nil?
+  end
+
+  def clone_directory
+    @clone_directory ||= File.join Dir.tmpdir, "kamal-clones", [ service, pwd_sha ].compact.join("-")
+  end
+
+  def build_directory
+    @build_directory ||=
+      if git_clone?
+        File.join clone_directory, repo_basename, repo_relative_pwd
+      else
+        "."
+      end
+  end
+
+  private
+    def cache_image
+      builder_config["cache"]&.fetch("image", nil) || "#{image}-build-cache"
+    end
+
+    def cache_image_ref
+      [ server, cache_image ].compact.join("/")
+    end
+
+    def cache_from_config_for_gha
+      "type=gha"
+    end
+
+    def cache_from_config_for_registry
+      [ "type=registry", "ref=#{cache_image_ref}" ].compact.join(",")
+    end
+
+    def cache_to_config_for_gha
+      [ "type=gha", builder_config["cache"]&.fetch("options", nil) ].compact.join(",")
+    end
+
+    def cache_to_config_for_registry
+      [ "type=registry", builder_config["cache"]&.fetch("options", nil), "ref=#{cache_image_ref}" ].compact.join(",")
+    end
+
+    def repo_basename
+      File.basename(Kamal::Git.root)
+    end
+
+    def repo_relative_pwd
+      Dir.pwd.delete_prefix(Kamal::Git.root)
+    end
+
+    def pwd_sha
+      Digest::SHA256.hexdigest(Dir.pwd)[0..12]
+    end
+end

lib/kamal/configuration/docs/accessory.yml

@@ -0,0 +1,90 @@
+# Accessories
+#
+# Accessories can be booted on a single host, a list of hosts, or on specific roles.
+# The hosts do not need to be defined in the Kamal servers configuration.
+#
+# Accessories are managed separately from the main service - they are not updated
+# when you deploy and they do not have zero-downtime deployments.
+#
+# Run `kamal accessory boot <accessory>` to boot an accessory.
+# See `kamal accessory --help` for more information.
+
+# Configuring accessories
+#
+# First define the accessory in the `accessories`
+accessories:
+  mysql:
+
+    # Service name
+    #
+    # This is used in the service label and defaults to `<service>-<accessory>`
+    # where `<service>` is the main service name from the root configuration
+    service: mysql
+
+    # Image
+    #
+    # The Docker image to use, prefix with a registry if not using Docker hub
+    image: mysql:8.0
+
+    # Accessory hosts
+    #
+    # Specify one  of `host`, `hosts` or `roles`
+    host: mysql-db1
+    hosts:
+      - mysql-db1
+      - mysql-db2
+    roles:
+      - mysql
+
+    # Custom command
+    #
+    # You can set a custom command to run in the container, if you do not want to use the default
+    cmd: "bin/mysqld"
+
+    # Port mappings
+    #
+    # See https://docs.docker.com/network/, especially note the warning about the security
+    # implications of exposing ports publicly.
+    port: "127.0.0.1:3306:3306"
+
+    # Labels
+    labels:
+      app: myapp
+
+    # Options
+    # These are passed to the Docker run command in the form `--<name> <value>`
+    options:
+      restart: always
+      cpus: 2
+
+    # Environment variables
+    # See kamal docs env for more information
+    env:
+      ...
+
+    # Copying files
+    #
+    # You can specify files to mount into the container.
+    # The format is `local:remote` where `local` is the path to the file on the local machine
+    # and `remote` is the path to the file in the container.
+    #
+    # They will be uploaded from the local repo to the host and then mounted.
+    #
+    # ERB files will be evaluated before being copied.
+    files:
+      - config/my.cnf.erb:/etc/mysql/my.cnf
+      - config/myoptions.cnf:/etc/mysql/myoptions.cnf
+
+    # Directories
+    #
+    # You can specify directories to mount into the container. They will be created on the host
+    # before being mounted
+    directories:
+      - mysql-logs:/var/log/mysql
+
+    # Volumes
+    #
+    # Any other volumes to mount, in addition to the files and directories.
+    # They are not created or copied before mounting
+    volumes:
+      - /path/to/mysql-logs:/var/log/mysql

lib/kamal/configuration/docs/boot.yml

@@ -0,0 +1,19 @@
+# Booting
+#
+# When deploying to large numbers of hosts, you might prefer not to restart your services on every host at the same time.
+#
+# Kamal’s default is to boot new containers on all hosts in parallel. But you can control this with the boot configuration.
+
+# Fixed group sizes
+#
+# Here we boot 2 hosts at a time with a 10 second gap between each group.
+boot:
+  limit: 2
+  wait: 10
+
+# Percentage of hosts
+#
+# Here we boot 25% of the hosts at a time with a 2 second gap between each group.
+boot:
+  limit: 25%
+  wait: 2

lib/kamal/configuration/docs/builder.yml

@@ -0,0 +1,107 @@
+# Builder
+#
+# The builder configuration controls how the application is built with `docker build` or `docker buildx build`
+#
+# If no configuration is specified, Kamal will:
+# 1. Create a buildx context called `kamal-<service>-multiarch`
+# 2. Use `docker buildx build` to build a multiarch image for linux/amd64,linux/arm64 with that context
+#
+# See https://kamal-deploy.org/docs/configuration/builder-examples/ for more information
+
+# Builder options
+#
+# Options go under the builder key in the root configuration.
+builder:
+
+  # Multiarch
+  #
+  # Enables multiarch builds, defaults to `true`
+  multiarch: false
+
+  # Local configuration
+  #
+  # The build configuration for local builds, only used if multiarch is enabled (the default)
+  #
+  # If there is no remote configuration, by default we build for amd64 and arm64.
+  # If you only want to build for one architecture, you can specify it here.
+  # The docker socket is optional and uses the default docker host socket when not specified
+  local:
+    arch: amd64
+    host: /var/run/docker.sock
+
+  # Remote configuration
+  #
+  # The build configuration for remote builds, also only used if multiarch is enabled.
+  # The arch is required and can be either amd64 or arm64.
+  remote:
+    arch: arm64
+    host: ssh://docker@docker-builder
+
+  # Builder cache
+  #
+  # The type must be either 'gha' or 'registry'
+  #
+  # The image is only used for registry cache
+  cache:
+    type: registry
+    options: mode=max
+    image: kamal-app-build-cache
+
+  # Build context
+  #
+  # If this is not set, then a local git clone of the repo is used.
+  # This ensures a clean build with no uncommitted changes.
+  #
+  # To use the local checkout instead you can set the context to `.`, or a path to another directory.
+  context: .
+
+  # Dockerfile
+  #
+  # The Dockerfile to use for building, defaults to `Dockerfile`
+  dockerfile: Dockerfile.production
+
+  # Build target
+  #
+  # If not set, then the default target is used
+  target: production
+
+  # Build Arguments
+  #
+  # Any additional build arguments, passed to `docker build` with `--build-arg <key>=<value>`
+  args:
+    ENVIRONMENT: production
+
+  # Referencing build arguments
+  #
+  # ```shell
+  # ARG RUBY_VERSION
+  # FROM ruby:$RUBY_VERSION-slim as base
+  # ```
+
+  # Build secrets
+  #
+  # Values are read from the environment.
+  #
+  secrets:
+    - SECRET1
+    - SECRET2
+
+  # Referencing Build Secrets
+  #
+  # ```shell
+  # # Copy Gemfiles
+  # COPY Gemfile Gemfile.lock ./
+  #
+  # # Install dependencies, including private repositories via access token
+  # # Then remove bundle cache with exposed GITHUB_TOKEN)
+  # RUN --mount=type=secret,id=GITHUB_TOKEN \
+  #   BUNDLE_GITHUB__COM=x-access-token:$(cat /run/secrets/GITHUB_TOKEN) \
+  #   bundle install && \
+  #   rm -rf /usr/local/bundle/cache
+  # ```
+
+
+  # SSH
+  #
+  # SSH agent socket or keys to expose to the build
+  ssh: default=$SSH_AUTH_SOCK

lib/kamal/configuration/docs/configuration.yml

@@ -0,0 +1,164 @@
+# Kamal Configuration
+#
+# Configuration is read from the `config/deploy.yml`
+#
+
+# Destinations
+#
+# When running commands, you can specify a destination with the `-d` flag,
+# e.g. `kamal deploy -d staging`
+#
+# In this case the configuration will also be read from `config/deploy.staging.yml`
+# and merged with the base configuration.
+
+# Extensions
+#
+# Kamal will not accept unrecognized keys in the configuration file.
+#
+# However, you might want to declare a configuration block using YAML anchors
+# and aliases to avoid repetition.
+#
+# You can use prefix a configuration section with `x-` to indicate that it is an
+# extension. Kamal will ignore the extension and not raise an error.
+
+# The service name
+# This is a required value. It is used as the container name prefix.
+service: myapp
+
+# The Docker image name
+#
+# The image will be pushed to the configured registry.
+image: my-image
+
+# Labels
+#
+# Additional labels to add to the container
+labels:
+  my-label: my-value
+
+# Additional volumes to mount into the container
+volumes:
+  - /path/on/host:/path/in/container:ro
+
+# Registry
+#
+# The Docker registry configuration, see kamal docs registry
+registry:
+  ...
+
+# Servers
+#
+# The servers to deploy to, optionally with custom roles, see kamal docs servers
+servers:
+  ...
+
+# Environment variables
+#
+# See kamal docs env
+env:
+  ...
+
+# Asset Bridging
+#
+# Used for asset bridging across deployments, default to `nil`
+#
+# If there are changes to CSS or JS files, we may get requests
+# for the old versions on the new container and vice-versa.
+#
+# To avoid 404s we can specify an asset path.
+# Kamal will replace that path in the container with a mapped
+# volume containing both sets of files.
+# This requires that file names change when the contents change
+# (e.g. by including a hash of the contents in the name).
+
+# To configure this, set the path to the assets:
+asset_path: /path/to/assets
+
+# Require destinations
+#
+# Whether deployments require a destination to be specified, defaults to `false`
+require_destination: true
+
+# The primary role
+#
+# This defaults to `web`, but if you have no web role, you can change this
+primary_role: workers
+
+# Allowing empty roles
+#
+# Whether roles with no servers are allowed. Defaults to `false`.
+allow_empty_roles: false
+
+# Stop wait time
+#
+# How long we wait for a container to stop before killing it, defaults to 30 seconds
+stop_wait_time: 60
+
+# Retain containers
+#
+# How many old containers and images we retain, defaults to 5
+retain_containers: 3
+
+# Minimum version
+#
+# The minimum version of Kamal required to deploy this configuration, defaults to nil
+minimum_version: 1.3.0
+
+# Readiness delay
+#
+# Seconds to wait for a container to boot after is running, default 7
+# This only applies to containers that do not specify a healthcheck
+readiness_delay: 4
+
+# Run directory
+#
+# Directory to store kamal runtime files in on the host, default `.kamal`
+run_directory: /etc/kamal
+
+# SSH options
+#
+# See kamal docs ssh
+ssh:
+  ...
+
+# Builder options
+#
+# See kamal docs builder
+builder:
+  ...
+
+# Accessories
+#
+# Additionals services to run in Docker, see kamal docs accessory
+accessories:
+  ...
+
+# Traefik
+#
+# The Traefik proxy is used for zero-downtime deployments, see kamal docs traefik
+traefik:
+  ...
+
+# SSHKit
+#
+# See kamal docs sshkit
+sshkit:
+  ...
+
+# Boot options
+#
+# See kamal docs boot
+boot:
+  ...
+
+# Healthcheck
+#
+# Configuring healthcheck commands, intervals and timeouts, see kamal docs healthcheck
+healthcheck:
+  ...
+
+# Logging
+#
+# Docker logging configuration, see kamal docs logging
+logging:
+  ...

lib/kamal/configuration/docs/env.yml

@@ -0,0 +1,72 @@
+# Environment variables
+#
+# Environment variables can be set directory in the Kamal configuration or
+# for loaded from a .env file, for secrets that should not be checked into Git.
+
+# Reading environment variables from the configuration
+#
+# Environment variables can be set directly in the configuration file.
+#
+# These are passed to the docker run command when deploying.
+env:
+  DATABASE_HOST: mysql-db1
+  DATABASE_PORT: 3306
+
+# Using .env file to load required environment variables
+#
+# Kamal uses dotenv to automatically load environment variables set in the .env file present
+# in the application root.
+#
+# This file can be used to set variables like KAMAL_REGISTRY_PASSWORD or database passwords.
+# But for this reason you must ensure that .env files are not checked into Git or included
+# in your Dockerfile! The format is just key-value like:
+# ```
+# KAMAL_REGISTRY_PASSWORD=pw
+# DB_PASSWORD=secret123
+# ```
+# See https://kamal-deploy.org/docs/commands/env/ for how to use generated .env files.
+#
+# To pass the secrets you should list them under the `secret` key. When you do this the
+# other variables need to be moved under the `clear` key.
+#
+# Unlike clear values, secrets are not passed directly to the container,
+# but are stored in an env file on the host
+# The file is not updated when deploying, only when running `kamal env push`.
+env:
+  clear:
+    DB_USER: app
+  secret:
+    - DB_PASSWORD
+
+# Tags
+#
+# Tags are used to add extra env variables to specific hosts.
+# See kamal docs servers for how to tag hosts.
+#
+# Tags are only allowed in the top level env configuration (i.e not under a role specific env).
+#
+# The env variables can be specified with secret and clear values as explained above.
+env:
+  tags:
+    <tag1>:
+      MYSQL_USER: monitoring
+    <tag2>:
+      clear:
+        MYSQL_USER: readonly
+      secret:
+        - MYSQL_PASSWORD
+
+# Example configuration
+env:
+  clear:
+    MYSQL_USER: app
+  secret:
+    - MYSQL_PASSWORD
+  tags:
+    monitoring:
+      MYSQL_USER: monitoring
+    replica:
+      clear:
+        MYSQL_USER: readonly
+      secret:
+        - READONLY_PASSWORD

lib/kamal/configuration/docs/healthcheck.yml

@@ -0,0 +1,59 @@
+# Healthcheck configuration
+#
+# On roles that are running Traefik, Kamal will supply a default healthcheck to `docker run`.
+# For other roles, by default no healthcheck is supplied.
+#
+# If no healthcheck is supplied and the image does not define one, they we wait for the container
+# to reach a running state and then pause for the readiness delay.
+#
+# The default healthcheck is `curl -f http://localhost:<port>/<path>`, so it assumes that `curl`
+# is available within the container.
+
+# Healthcheck options
+#
+# These go under the `healthcheck` key in the root or role configuration.
+healthcheck:
+
+  # Command
+  #
+  # The command to run, defaults to `curl -f http://localhost:<port>/<path>` on roles running Traefik
+  cmd: "curl -f http://localhost"
+
+  # Interval
+  #
+  # The Docker healthcheck interval, defaults to `1s`
+  interval: 10s
+
+  # Max attempts
+  #
+  # The maximum number of times we poll the container to see if it is healthy, defaults to `7`
+  # Each check is separated by an increasing interval starting with 1 second.
+  max_attempts: 3
+
+  # Port
+  #
+  # The port to use in the healthcheck, defaults to `3000`
+  port: "80"
+
+  # Path
+  #
+  # The path to use in the healthcheck, defaults to `/up`
+  path: /health
+
+  # Cords for zero-downtime deployments
+  #
+  # The cord file is used for zero-downtime deployments. The healthcheck is augmented with a check
+  # for the existance of the file. This allows us to delete the file and force the container to
+  # become unhealthy, causing Traefik to stop routing traffic to it.
+  #
+  # Kamal mounts a volume at this location and creates the file before starting the container.
+  # You can set the value to `false` to disable the cord file, but this loses the zero-downtime
+  # guarantee.
+  #
+  # The default value is `/tmp/kamal-cord`
+  cord: /cord
+
+  # Log lines
+  #
+  # Number of lines to log from the container when the healthcheck fails, defaults to `50`
+  log_lines: 100

lib/kamal/configuration/docs/logging.yml

@@ -0,0 +1,21 @@
+# Custom logging configuration
+#
+# Set these to control the Docker logging driver and options.
+
+# Logging settings
+#
+# These go under the logging key in the configuration file.
+#
+# This can be specified in the root level or for a specific role.
+logging:
+
+  # Driver
+  #
+  # The logging driver to use, passed to Docker via `--log-driver`
+  driver: json-file
+
+  # Options
+  #
+  # Any logging options to pass to the driver, passed to Docker via `--log-opt`
+  options:
+    max-size: 100m

lib/kamal/configuration/docs/registry.yml

@@ -0,0 +1,49 @@
+# Registry
+#
+# The default registry is Docker Hub, but you can change it using registry/server:
+#
+# A reference to secret (in this case DOCKER_REGISTRY_TOKEN) will look up the secret
+# in the local environment.
+
+registry:
+  server: registry.digitalocean.com
+  username:
+    - DOCKER_REGISTRY_TOKEN
+  password:
+    - DOCKER_REGISTRY_TOKEN
+
+# Using AWS ECR as the container registry
+# You will need to have the aws CLI installed locally for this to work.
+# AWS ECR’s access token is only valid for 12hrs. In order to not have to manually regenerate the token every time, you can use ERB in the deploy.yml file to shell out to the aws cli command, and obtain the token:
+
+registry:
+  server: <your aws account id>.dkr.ecr.<your aws region id>.amazonaws.com
+  username: AWS
+  password: <%= %x(aws ecr get-login-password) %>
+
+# Using GCP Artifact Registry as the container registry
+# To sign into Artifact Registry, you would need to
+# [create a service account](https://cloud.google.com/iam/docs/service-accounts-create#creating)
+# and [set up roles and permissions](https://cloud.google.com/artifact-registry/docs/access-control#permissions).
+# Normally, assigning a roles/artifactregistry.writer role should be sufficient.
+#
+# Once the service account is ready, you need to generate and download a JSON key, base64 encode it and add to .env:
+#
+# ```shell
+# echo "KAMAL_REGISTRY_PASSWORD=$(base64 -i /path/to/key.json)" | tr -d "\\n"  >> .env
+# ```
+# Use the env variable as password along with _json_key_base64 as username.
+# Here’s the final configuration:
+
+registry:
+  server: <your registry region>-docker.pkg.dev
+  username: _json_key_base64
+  password:
+    - KAMAL_REGISTRY_PASSWORD
+
+# Validating the configuration
+#
+# You can validate the configuration by running:
+# ```shell
+# kamal registry login
+# ```

lib/kamal/configuration/docs/role.yml

@@ -0,0 +1,52 @@
+# Roles
+#
+# Roles are used to configure different types of servers in the deployment.
+# The most common use for this is to run a web servers and job servers.
+#
+# Kamal expects there to be a `web` role, unless you set a different `primary_role`
+# in the root configuration.
+
+# Role configuration
+#
+# Roles are specified under the servers key
+servers:
+
+  # Simple role configuration
+  #
+  #
+  # This can be a list of hosts, if you don't need custom configuration for the role.
+  #
+  # You can set tags on the hosts for custom env variables (see kamal docs env)
+  web:
+    - 172.1.0.1
+    - 172.1.0.2: experiment1
+    - 172.1.0.2: [ experiment1, experiment2 ]
+
+  # Custom role configuration
+  #
+  # When there are other options to set, the list of hosts goes under the `hosts` key
+  #
+  # By default only the primary role uses Traefik, but you can set `traefik` to change
+  # it.
+  #
+  # You can also set a custom cmd to run in the container, and overwrite other settings
+  # from the root configuration.
+  workers:
+    hosts:
+      - 172.1.0.3
+      - 172.1.0.4: experiment1
+    traefik: true
+    cmd: "bin/jobs"
+    options:
+      memory: 2g
+      cpus: 4
+    healthcheck:
+      ...
+    logging:
+      ...
+    labels:
+      my-label: workers
+    env:
+      ...
+    asset_path: /public
+

lib/kamal/configuration/docs/servers.yml

@@ -0,0 +1,27 @@
+# Servers
+#
+# Servers are split into different roles, with each role having its own configuration.
+#
+# For simpler deployments though where all servers are identical, you can just specify a list of servers
+# They will be implicitly assigned to the `web` role.
+servers:
+  - 172.0.0.1
+  - 172.0.0.2
+  - 172.0.0.3
+
+# Tagging servers
+#
+# Servers can be tagged, with the tags used to add custom env variables (see kamal docs env).
+servers:
+  - 172.0.0.1
+  - 172.0.0.2: experiments
+  - 172.0.0.3: [ experiments, three ]
+
+# Roles
+#
+# For more complex deployments (e.g. if you are running job hosts), you can specify roles, and configure each separately (see kamal docs role)
+servers:
+  web:
+    ...
+  workers:
+    ...

lib/kamal/configuration/docs/ssh.yml

@@ -0,0 +1,66 @@
+# SSH configuration
+#
+# Kamal uses SSH to connect run commands on your hosts.
+# By default it will attempt to connect to the root user on port 22
+#
+# If you are using non-root user, you may need to bootstrap your servers manually, before using them with Kamal. On Ubuntu, you’d do:
+#
+# ```shell
+# sudo apt update
+# sudo apt upgrade -y
+# sudo apt install -y docker.io curl git
+# sudo usermod -a -G docker app
+# ```
+
+
+# SSH options
+#
+# The options are specified under the ssh key in the configuration file.
+ssh:
+
+  # The SSH user
+  #
+  # Defaults to `root`
+  #
+  user: app
+
+  # The SSH port
+  #
+  # Defaults to 22
+  port: "2222"
+
+  # Proxy host
+  #
+  # Specified in the form <host> or <user>@<host>
+  proxy: root@proxy-host
+
+  # Proxy command
+  #
+  # A custom proxy command, required for older versions of SSH
+  proxy_command: "ssh -W %h:%p user@proxy"
+
+  # Log level
+  #
+  # Defaults to `fatal`. Set this to debug if you are having
+  # SSH connection issues.
+  log_level: debug
+
+  # Keys Only
+  #
+  # Set to true to use only private keys from keys and key_data parameters, 
+  # even if ssh-agent offers more identities. This option is intended for 
+  # situations where ssh-agent offers many different identites or you have 
+  # a need to overwrite all identites and force a single one.
+  keys_only: false
+
+  # Keys
+  #
+  # An array of file names of private keys to use for publickey
+  # and hostbased authentication
+  keys: [ "~/.ssh/id.pem" ]
+
+  # Key Data
+  #
+  # An array of strings, with each element of the array being
+  # a raw private key in PEM format.
+  key_data: [ "-----BEGIN OPENSSH PRIVATE KEY-----" ]

lib/kamal/configuration/docs/sshkit.yml

@@ -0,0 +1,23 @@
+# SSHKit
+#
+# [SSHKit](https://github.com/capistrano/sshkit) is the SSH toolkit used by Kamal.
+#
+# The default settings should be sufficient for most use cases, but
+# when connecting to a large number of hosts you may need to adjust
+
+# SSHKit options
+#
+# The options are specified under the sshkit key in the configuration file.
+sshkit:
+
+  # Max concurrent starts
+  #
+  # Creating SSH connections concurrently can be an issue when deploying to many servers.
+  # By default Kamal will limit concurrent connection starts to 30 at a time.
+  max_concurrent_starts: 10
+
+  # Pool idle timeout
+  #
+  # Kamal sets a long idle timeout of 900 seconds on connections to try to avoid
+  # re-connection storms after an idle period, like building an image or waiting for CI.
+  pool_idle_timeout: 300

lib/kamal/configuration/docs/traefik.yml

@@ -0,0 +1,62 @@
+# Traefik
+#
+# Traefik is a reverse proxy, used by Kamal for zero-downtime deployments.
+#
+# We start an instance on the hosts in it's own container.
+#
+# During a deployment:
+# 1. We start a new container which Traefik automatically detects due to the labels we have applied
+# 2. Traefik starts routing traffic to the new container
+# 3. We force the old container to fail it's healthcheck, causing Traefik to stop routing traffic to it
+# 4. We stop the old container
+
+# Traefik settings
+#
+# Traekik is configured in the root configuration under `traefik`.
+traefik:
+
+  # Image
+  #
+  # The Traefik image to use, defaults to `traefik:v2.10`
+  image: traefik:v2.9
+
+  # Host port
+  #
+  # The host port to publish the Traefik container on, defaults to `80`
+  host_port: "8080"
+
+  # Disabling publishing
+  #
+  # To avoid publishing the Traefik container, set this to `false`
+  publish: false
+
+  # Labels
+  #
+  # Additional labels to apply to the Traefik container
+  labels:
+    traefik.http.routers.catchall.entryPoints: http
+    traefik.http.routers.catchall.rule: PathPrefix(`/`)
+    traefik.http.routers.catchall.service: unavailable
+    traefik.http.routers.catchall.priority: "1"
+    traefik.http.services.unavailable.loadbalancer.server.port: "0"
+
+  # Arguments
+  #
+  # Additional arguments to pass to the Traefik container
+  args:
+    entryPoints.http.address: ":80"
+    entryPoints.http.forwardedHeaders.insecure: true
+    accesslog: true
+    accesslog.format: json
+
+  # Options
+  #
+  # Additional options to pass to `docker run`
+  options:
+    cpus: 2
+
+  # Environment variables
+  #
+  # See kamal docs env
+  env:
+    ...

lib/kamal/configuration/env.rb

@@ -0,0 +1,36 @@
+class Kamal::Configuration::Env
+  include Kamal::Configuration::Validation
+
+  attr_reader :secrets_keys, :clear, :secrets_file, :context
+  delegate :argumentize, to: Kamal::Utils
+
+  def initialize(config:, secrets_file: nil, context: "env")
+    @clear = config.fetch("clear", config.key?("secret") || config.key?("tags") ? {} : config)
+    @secrets_keys = config.fetch("secret", [])
+    @secrets_file = secrets_file
+    @context = context
+    validate! config, context: context, with: Kamal::Configuration::Validator::Env
+  end
+
+  def args
+    [ "--env-file", secrets_file, *argumentize("--env", clear) ]
+  end
+
+  def secrets_io
+    StringIO.new(Kamal::EnvFile.new(secrets).to_s)
+  end
+
+  def secrets
+    @secrets ||= secrets_keys.to_h { |key| [ key, ENV.fetch(key) ] }
+  end
+
+  def secrets_directory
+    File.dirname(secrets_file)
+  end
+
+  def merge(other)
+    self.class.new \
+      config: { "clear" => clear.merge(other.clear), "secret" => secrets_keys | other.secrets_keys },
+      secrets_file: secrets_file || other.secrets_file
+  end
+end

lib/kamal/configuration/env/tag.rb

@@ -0,0 +1,12 @@
+class Kamal::Configuration::Env::Tag
+  attr_reader :name, :config
+
+  def initialize(name, config:)
+    @name = name
+    @config = config
+  end
+
+  def env
+    Kamal::Configuration::Env.new(config: config)
+  end
+end

lib/kamal/configuration/healthcheck.rb

@@ -0,0 +1,63 @@
+class Kamal::Configuration::Healthcheck
+  include Kamal::Configuration::Validation
+
+  attr_reader :healthcheck_config
+
+  def initialize(healthcheck_config:, context: "healthcheck")
+    @healthcheck_config = healthcheck_config || {}
+    validate! @healthcheck_config, context: context
+  end
+
+  def merge(other)
+    self.class.new healthcheck_config: healthcheck_config.deep_merge(other.healthcheck_config)
+  end
+
+  def cmd
+    healthcheck_config.fetch("cmd", http_health_check)
+  end
+
+  def port
+    healthcheck_config.fetch("port", 3000)
+  end
+
+  def path
+    healthcheck_config.fetch("path", "/up")
+  end
+
+  def max_attempts
+    healthcheck_config.fetch("max_attempts", 7)
+  end
+
+  def interval
+    healthcheck_config.fetch("interval", "1s")
+  end
+
+  def cord
+    healthcheck_config.fetch("cord", "/tmp/kamal-cord")
+  end
+
+  def log_lines
+    healthcheck_config.fetch("log_lines", 50)
+  end
+
+  def set_port_or_path?
+    healthcheck_config["port"].present? || healthcheck_config["path"].present?
+  end
+
+  def to_h
+    {
+      "cmd" => cmd,
+      "interval" => interval,
+      "max_attempts" => max_attempts,
+      "port" => port,
+      "path" => path,
+      "cord" => cord,
+      "log_lines" => log_lines
+    }
+  end
+
+  private
+    def http_health_check
+      "curl -f #{URI.join("http://localhost:#{port}", path)} || exit 1" if path.present? || port.present?
+    end
+end

lib/kamal/configuration/logging.rb

@@ -0,0 +1,33 @@
+class Kamal::Configuration::Logging
+  delegate :optionize, :argumentize, to: Kamal::Utils
+
+  include Kamal::Configuration::Validation
+
+  attr_reader :logging_config
+
+  def initialize(logging_config:, context: "logging")
+    @logging_config = logging_config || {}
+    validate! @logging_config, context: context
+  end
+
+  def driver
+    logging_config["driver"]
+  end
+
+  def options
+    logging_config.fetch("options", {})
+  end
+
+  def merge(other)
+    self.class.new logging_config: logging_config.deep_merge(other.logging_config)
+  end
+
+  def args
+    if driver.present? || options.present?
+      optionize({ "log-driver" => driver }.compact) +
+        argumentize("--log-opt", options)
+    else
+      argumentize("--log-opt", { "max-size" => "10m" })
+    end
+  end
+end

lib/kamal/configuration/registry.rb

@@ -0,0 +1,31 @@
+class Kamal::Configuration::Registry
+  include Kamal::Configuration::Validation
+
+  attr_reader :registry_config
+
+  def initialize(config:)
+    @registry_config = config.raw_config.registry || {}
+    validate! registry_config, with: Kamal::Configuration::Validator::Registry
+  end
+
+  def server
+    registry_config["server"]
+  end
+
+  def username
+    lookup("username")
+  end
+
+  def password
+    lookup("password")
+  end
+
+  private
+    def lookup(key)
+      if registry_config[key].is_a?(Array)
+        ENV.fetch(registry_config[key].first).dup
+      else
+        registry_config[key]
+      end
+    end
+end

lib/kamal/configuration/role.rb

@@ -0,0 +1,251 @@
+class Kamal::Configuration::Role
+  include Kamal::Configuration::Validation
+
+  CORD_FILE = "cord"
+  delegate :argumentize, :optionize, to: Kamal::Utils
+
+  attr_reader :name, :config, :specialized_env, :specialized_logging, :specialized_healthcheck
+
+  alias to_s name
+
+  def initialize(name, config:)
+    @name, @config = name.inquiry, config
+    validate! \
+      specializations,
+      example: validation_yml["servers"]["workers"],
+      context: "servers/#{name}",
+      with: Kamal::Configuration::Validator::Role
+
+    @specialized_env = Kamal::Configuration::Env.new \
+      config: specializations.fetch("env", {}),
+      secrets_file: File.join(config.host_env_directory, "roles", "#{container_prefix}.env"),
+      context: "servers/#{name}/env"
+
+    @specialized_logging = Kamal::Configuration::Logging.new \
+      logging_config: specializations.fetch("logging", {}),
+      context: "servers/#{name}/logging"
+
+    @specialized_healthcheck = Kamal::Configuration::Healthcheck.new \
+      healthcheck_config: specializations.fetch("healthcheck", {}),
+      context: "servers/#{name}/healthcheck"
+  end
+
+  def primary_host
+    hosts.first
+  end
+
+  def hosts
+    tagged_hosts.keys
+  end
+
+  def env_tags(host)
+    tagged_hosts.fetch(host).collect { |tag| config.env_tag(tag) }
+  end
+
+  def cmd
+    specializations["cmd"]
+  end
+
+  def option_args
+    if args = specializations["options"]
+      optionize args
+    else
+      []
+    end
+  end
+
+  def labels
+    default_labels.merge(traefik_labels).merge(custom_labels)
+  end
+
+  def label_args
+    argumentize "--label", labels
+  end
+
+  def logging_args
+    logging.args
+  end
+
+  def logging
+    @logging ||= config.logging.merge(specialized_logging)
+  end
+
+
+  def env(host)
+    @envs ||= {}
+    @envs[host] ||= [ config.env, specialized_env, *env_tags(host).map(&:env) ].reduce(:merge)
+  end
+
+  def env_args(host)
+    env(host).args
+  end
+
+  def asset_volume_args
+    asset_volume&.docker_args
+  end
+
+
+  def health_check_args(cord: true)
+    if running_traefik? || healthcheck.set_port_or_path?
+      if cord && uses_cord?
+        optionize({ "health-cmd" => health_check_cmd_with_cord, "health-interval" => healthcheck.interval })
+          .concat(cord_volume.docker_args)
+      else
+        optionize({ "health-cmd" => healthcheck.cmd, "health-interval" => healthcheck.interval })
+      end
+    else
+      []
+    end
+  end
+
+  def healthcheck
+    @healthcheck ||=
+      if running_traefik?
+        config.healthcheck.merge(specialized_healthcheck)
+      else
+        specialized_healthcheck
+      end
+  end
+
+  def health_check_cmd_with_cord
+    "(#{healthcheck.cmd}) && (stat #{cord_container_file} > /dev/null || exit 1)"
+  end
+
+
+  def running_traefik?
+    if specializations["traefik"].nil?
+      primary?
+    else
+      specializations["traefik"]
+    end
+  end
+
+  def primary?
+    self == @config.primary_role
+  end
+
+
+  def uses_cord?
+    running_traefik? && cord_volume && healthcheck.cmd.present?
+  end
+
+  def cord_host_directory
+    File.join config.run_directory_as_docker_volume, "cords", [ container_prefix, config.run_id ].join("-")
+  end
+
+  def cord_volume
+    if (cord = healthcheck.cord)
+      @cord_volume ||= Kamal::Configuration::Volume.new \
+        host_path: File.join(config.run_directory, "cords", [ container_prefix, config.run_id ].join("-")),
+        container_path: cord
+    end
+  end
+
+  def cord_host_file
+    File.join cord_volume.host_path, CORD_FILE
+  end
+
+  def cord_container_directory
+    health_check_options.fetch("cord", nil)
+  end
+
+  def cord_container_file
+    File.join cord_volume.container_path, CORD_FILE
+  end
+
+
+  def container_name(version = nil)
+    [ container_prefix, version || config.version ].compact.join("-")
+  end
+
+  def container_prefix
+    [ config.service, name, config.destination ].compact.join("-")
+  end
+
+
+  def asset_path
+    specializations["asset_path"] || config.asset_path
+  end
+
+  def assets?
+    asset_path.present? && running_traefik?
+  end
+
+  def asset_volume(version = nil)
+    if assets?
+      Kamal::Configuration::Volume.new \
+        host_path: asset_volume_path(version), container_path: asset_path
+    end
+  end
+
+  def asset_extracted_path(version = nil)
+    File.join config.run_directory, "assets", "extracted", container_name(version)
+  end
+
+  def asset_volume_path(version = nil)
+    File.join config.run_directory, "assets", "volumes", container_name(version)
+  end
+
+  private
+    def tagged_hosts
+      {}.tap do |tagged_hosts|
+        extract_hosts_from_config.map do |host_config|
+          if host_config.is_a?(Hash)
+            host, tags = host_config.first
+            tagged_hosts[host] = Array(tags)
+          elsif host_config.is_a?(String)
+            tagged_hosts[host_config] = []
+          end
+        end
+      end
+    end
+
+    def extract_hosts_from_config
+      if config.raw_config.servers.is_a?(Array)
+        config.raw_config.servers
+      else
+        servers = config.raw_config.servers[name]
+        servers.is_a?(Array) ? servers : Array(servers["hosts"])
+      end
+    end
+
+    def default_labels
+      { "service" => config.service, "role" => name, "destination" => config.destination }
+    end
+
+    def specializations
+      if config.raw_config.servers.is_a?(Array) || config.raw_config.servers[name].is_a?(Array)
+        {}
+      else
+        config.raw_config.servers[name]
+      end
+    end
+
+    def traefik_labels
+      if running_traefik?
+        {
+          # Setting a service property ensures that the generated service name will be consistent between versions
+          "traefik.http.services.#{traefik_service}.loadbalancer.server.scheme" => "http",
+
+          "traefik.http.routers.#{traefik_service}.rule" => "PathPrefix(`/`)",
+          "traefik.http.routers.#{traefik_service}.priority" => "2",
+          "traefik.http.middlewares.#{traefik_service}-retry.retry.attempts" => "5",
+          "traefik.http.middlewares.#{traefik_service}-retry.retry.initialinterval" => "500ms",
+          "traefik.http.routers.#{traefik_service}.middlewares" => "#{traefik_service}-retry@docker"
+        }
+      else
+        {}
+      end
+    end
+
+    def traefik_service
+      container_prefix
+    end
+
+    def custom_labels
+      Hash.new.tap do |labels|
+        labels.merge!(config.labels) if config.labels.present?
+        labels.merge!(specializations["labels"]) if specializations["labels"].present?
+      end
+    end
+end

lib/kamal/configuration/servers.rb

@@ -0,0 +1,18 @@
+class Kamal::Configuration::Servers
+  include Kamal::Configuration::Validation
+
+  attr_reader :config, :servers_config, :roles
+
+  def initialize(config:)
+    @config = config
+    @servers_config = config.raw_config.servers
+    validate! servers_config, with: Kamal::Configuration::Validator::Servers
+
+    @roles = role_names.map { |role_name| Kamal::Configuration::Role.new role_name, config: config }
+  end
+
+  private
+    def role_names
+      servers_config.is_a?(Array) ? [ "web" ] : servers_config.keys.sort
+    end
+end

lib/kamal/configuration/ssh.rb

@@ -0,0 +1,57 @@
+class Kamal::Configuration::Ssh
+  LOGGER = ::Logger.new(STDERR)
+
+  include Kamal::Configuration::Validation
+
+  attr_reader :ssh_config
+
+  def initialize(config:)
+    @ssh_config = config.raw_config.ssh || {}
+    validate! ssh_config
+  end
+
+  def user
+    ssh_config.fetch("user", "root")
+  end
+
+  def port
+    ssh_config.fetch("port", 22)
+  end
+
+  def proxy
+    if (proxy = ssh_config["proxy"])
+      Net::SSH::Proxy::Jump.new(proxy.include?("@") ? proxy : "root@#{proxy}")
+    elsif (proxy_command = ssh_config["proxy_command"])
+      Net::SSH::Proxy::Command.new(proxy_command)
+    end
+  end
+
+  def keys_only
+    ssh_config["keys_only"]
+  end
+
+  def keys
+    ssh_config["keys"]
+  end
+
+  def key_data
+    ssh_config["key_data"]
+  end
+
+  def options
+    { user: user, port: port, proxy: proxy, logger: logger, keepalive: true, keepalive_interval: 30, keys_only: keys_only, keys: keys, key_data: key_data }.compact
+  end
+
+  def to_h
+    options.except(:logger).merge(log_level: log_level)
+  end
+
+  private
+    def logger
+      LOGGER.tap { |logger| logger.level = log_level }
+    end
+
+    def log_level
+      ssh_config.fetch("log_level", :fatal)
+    end
+end

lib/kamal/configuration/sshkit.rb

@@ -0,0 +1,22 @@
+class Kamal::Configuration::Sshkit
+  include Kamal::Configuration::Validation
+
+  attr_reader :sshkit_config
+
+  def initialize(config:)
+    @sshkit_config = config.raw_config.sshkit || {}
+    validate! sshkit_config
+  end
+
+  def max_concurrent_starts
+    sshkit_config.fetch("max_concurrent_starts", 30)
+  end
+
+  def pool_idle_timeout
+    sshkit_config.fetch("pool_idle_timeout", 900)
+  end
+
+  def to_h
+    sshkit_config
+  end
+end

lib/kamal/configuration/traefik.rb

@@ -0,0 +1,60 @@
+class Kamal::Configuration::Traefik
+  DEFAULT_IMAGE = "traefik:v2.10"
+  CONTAINER_PORT = 80
+  DEFAULT_ARGS = {
+    "log.level" => "DEBUG"
+  }
+  DEFAULT_LABELS = {
+    # These ensure we serve a 502 rather than a 404 if no containers are available
+    "traefik.http.routers.catchall.entryPoints" => "http",
+    "traefik.http.routers.catchall.rule" => "PathPrefix(`/`)",
+    "traefik.http.routers.catchall.service" => "unavailable",
+    "traefik.http.routers.catchall.priority" => 1,
+    "traefik.http.services.unavailable.loadbalancer.server.port" => "0"
+  }
+
+  include Kamal::Configuration::Validation
+
+  attr_reader :config, :traefik_config
+
+  def initialize(config:)
+    @config = config
+    @traefik_config = config.raw_config.traefik || {}
+    validate! traefik_config
+  end
+
+  def publish?
+    traefik_config["publish"] != false
+  end
+
+  def labels
+    DEFAULT_LABELS.merge(traefik_config["labels"] || {})
+  end
+
+  def env
+    Kamal::Configuration::Env.new \
+      config: traefik_config.fetch("env", {}),
+      secrets_file: File.join(config.host_env_directory, "traefik", "traefik.env"),
+      context: "traefik/env"
+  end
+
+  def host_port
+    traefik_config.fetch("host_port", CONTAINER_PORT)
+  end
+
+  def options
+    traefik_config.fetch("options", {})
+  end
+
+  def port
+    "#{host_port}:#{CONTAINER_PORT}"
+  end
+
+  def args
+    DEFAULT_ARGS.merge(traefik_config.fetch("args", {}))
+  end
+
+  def image
+    traefik_config.fetch("image", DEFAULT_IMAGE)
+  end
+end

lib/kamal/configuration/validation.rb

@@ -0,0 +1,27 @@
+require "yaml"
+require "active_support/inflector"
+
+module Kamal::Configuration::Validation
+  extend ActiveSupport::Concern
+
+  class_methods do
+    def validation_doc
+      @validation_doc ||= File.read(File.join(File.dirname(__FILE__), "docs", "#{validation_config_key}.yml"))
+    end
+
+    def validation_config_key
+      @validation_config_key ||= name.demodulize.underscore
+    end
+  end
+
+  def validate!(config, example: nil, context: nil, with: Kamal::Configuration::Validator)
+    context ||= self.class.validation_config_key
+    example ||= validation_yml[self.class.validation_config_key]
+
+    with.new(config, example: example, context: context).validate!
+  end
+
+  def validation_yml
+    @validation_yml ||= YAML.load(self.class.validation_doc)
+  end
+end

lib/kamal/configuration/validator.rb

@@ -0,0 +1,153 @@
+class Kamal::Configuration::Validator
+  attr_reader :config, :example, :context
+
+  def initialize(config, example:, context:)
+    @config = config
+    @example = example
+    @context = context
+  end
+
+  def validate!
+    validate_against_example! config, example
+  end
+
+  private
+    def validate_against_example!(validation_config, example)
+      validate_type! validation_config, Hash
+
+      check_unknown_keys! validation_config, example
+
+      validation_config.each do |key, value|
+        next if extension?(key)
+        with_context(key) do
+          example_value = example[key]
+
+          if example_value == "..."
+            validate_type! value, *(Array if key == :servers), Hash
+          elsif key == "hosts"
+            validate_servers! value
+          elsif example_value.is_a?(Array)
+            validate_array_of! value, example_value.first.class
+          elsif example_value.is_a?(Hash)
+            case key.to_s
+            when "options", "args"
+              validate_type! value, Hash
+            when "labels"
+              validate_hash_of! value, example_value.first[1].class
+            else
+              validate_against_example! value, example_value
+            end
+          else
+            validate_type! value, example_value.class
+          end
+        end
+      end
+    end
+
+
+    def valid_type?(value, type)
+      value.is_a?(type) ||
+        (type == String && stringish?(value)) ||
+        (boolean?(type) && boolean?(value.class))
+    end
+
+    def type_description(type)
+      if type == Integer || type == Array
+        "an #{type.name.downcase}"
+      elsif type == TrueClass || type == FalseClass
+        "a boolean"
+      else
+        "a #{type.name.downcase}"
+      end
+    end
+
+    def boolean?(type)
+      type == TrueClass || type == FalseClass
+    end
+
+    def stringish?(value)
+      value.is_a?(String) || value.is_a?(Symbol) || value.is_a?(Numeric) || value.is_a?(TrueClass) || value.is_a?(FalseClass)
+    end
+
+    def validate_array_of!(array, type)
+      validate_type! array, Array
+
+      array.each_with_index do |value, index|
+        with_context(index) do
+          validate_type! value, type
+        end
+      end
+    end
+
+    def validate_hash_of!(hash, type)
+      validate_type! hash, Hash
+
+      hash.each do |key, value|
+        with_context(key) do
+          validate_type! value, type
+        end
+      end
+    end
+
+    def validate_servers!(servers)
+      validate_type! servers, Array
+
+      servers.each_with_index do |server, index|
+        with_context(index) do
+          validate_type! server, String, Hash
+
+          if server.is_a?(Hash)
+            error "multiple hosts found" unless server.size == 1
+            host, tags = server.first
+
+            with_context(host) do
+              validate_type! tags, String, Array
+              validate_array_of! tags, String if tags.is_a?(Array)
+            end
+          end
+        end
+      end
+    end
+
+    def validate_type!(value, *types)
+      type_error(*types) unless types.any? { |type| valid_type?(value, type) }
+    end
+
+    def error(message)
+      raise Kamal::ConfigurationError, "#{error_context}#{message}"
+    end
+
+    def type_error(*expected_types)
+      error "should be #{expected_types.map { |type| type_description(type) }.join(" or ")}"
+    end
+
+    def unknown_keys_error(unknown_keys)
+      error "unknown #{"key".pluralize(unknown_keys.count)}: #{unknown_keys.join(", ")}"
+    end
+
+    def error_context
+      "#{context}: " if context.present?
+    end
+
+    def with_context(context)
+      old_context = @context
+      @context = [ @context, context ].select(&:present?).join("/")
+      yield
+    ensure
+      @context = old_context
+    end
+
+    def allow_extensions?
+      false
+    end
+
+    def extension?(key)
+      key.to_s.start_with?("x-")
+    end
+
+    def check_unknown_keys!(config, example)
+      unknown_keys = config.keys - example.keys
+      unknown_keys.reject! { |key| extension?(key) } if allow_extensions?
+      unknown_keys_error unknown_keys if unknown_keys.present?
+    end
+end