# MRSK MRSK ships zero-downtime deploys of Rails apps packed as containers to any host. It uses the dynamic reverse-proxy Traefik to hold requests while the new application container is started and the old one is wound down. It works across multiple hosts at the same time, using SSHKit to execute commands. ## Installation Add the gem with `bundle add mrsk`, then run `rake mrsk:init`, and then edit the new file in `config/deploy.yml` to use the proper service name, image reference, servers to deploy on, and so on. It could look something like this: ```yaml service: hey image: 37s/hey servers: - xxx.xxx.xxx.xxx - xxx.xxx.xxx.xxx env: DATABASE_URL: mysql2://db1/hey_production/ REDIS_URL: redis://redis1:6379/1 registry: server: registry.digitalocean.com username: <%= Rails.application.credentials.registry["username"] %> password: <%= Rails.application.credentials.registry["password"] %> ``` Then ensure your encrypted credentials have the registry username + password by editing them with `rails credentials:edit`: ``` registry: username: real-user-name password: real-password ``` Now you're ready to deploy a multi-arch image (FIXME: currently you need to manually run `docker buildx create --use` once first): ``` rake mrsk:deploy ``` This will: 1. Log into the registry both locally and remotely 2. Build the image using the standard Dockerfile in the root of the application. 3. Push the image to the registry. 4. Pull the image from the registry on the servers. 5. Ensure Traefik is running and accepting traffic on port 80. 6. Stop any containers running a previous versions of the app. 7. Start a new container with the version of the app that matches the current git version hash. 8. 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. ## Operations ### Running job hosts separately If your application uses separate job running hosts, or other roles beyond the default web running, you can specify these hosts and their custom command like so: ```yaml servers: web: - xxx.xxx.xxx.xxx - xxx.xxx.xxx.xxx job: hosts: - xxx.xxx.xxx.xxx - xxx.xxx.xxx.xxx cmd: bin/jobs ``` The application will be deployed to all hosts, but only those in the `web` role will be labeled to run under traefik. If you want to run custom commands on all hosts in a role, you can use `rake mrsk:app:exec:rails CMD=about ROLES=job`. ### Executing commands If you need to execute commands inside the Rails containers, you can use `rake mrsk:app:exec`, `rake mrsk:app:exec:once`, `rake mrsk:app:exec:rails`, and `rake mrsk:app:exec:once:rails`. Examples: ```bash # Runs command on all servers rake mrsk:app:exec CMD='ruby -v' App Host: xxx.xxx.xxx.xxx ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [x86_64-linux] App Host: xxx.xxx.xxx.xxx ruby 3.1.3p185 (2022-11-24 revision 1a6b16756e) [x86_64-linux] # Runs command on first server rake mrsk:app:exec:once CMD='cat .ruby-version' 3.1.3 # Runs Rails command on all servers rake mrsk:app:exec:rails CMD=about App Host: xxx.xxx.xxx.xxx 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: xxx.xxx.xxx.xxx 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 # Runs Rails command on first server rake mrsk:app:exec:once:rails CMD='db:version' database: storage/production.sqlite3 Current version: 20221231233303 ``` ### Inspecting You can see the state of your servers by running `rake mrsk:info`. It'll show something like this: ``` Traefik Host: xxx.xxx.xxx.xxx 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: 164.92.105.119 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: 164.90.145.60 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: 164.92.105.119 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 `rake mrsk:app:info` or just for Traefik with `rake mrsk:traefik:info`. ### Rollback 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 `rake mrsk:app:containers`. It'll give you a presentation similar to `rake mrsk:app:info`, but include all the old containers as well. Showing something like this: ``` App Host: 164.92.105.119 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: 164.90.145.60 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 `rake mrsk:rollback VERSION=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 `rake mrsk:deploy`. ### Removing If you wish to remove the entire application, including Traefik, containers, images, and registry session, you can run `rake mrsk:remove`. This will leave the servers clean. ## Stage of development This is alpha software. Lots of stuff is missing. Here are some of the areas we seek to improve: - Adapterize commands to work with Podman and other container runners - Possibly switching to a bin/mrsk command rather than raw rake - Integrate with cloud CI pipelines ## License MRSK is released under the [MIT License](https://opensource.org/licenses/MIT).