Add a pre-connect hook

This can be used for hooks that should run before connecting to remote
hosts. An example use case is pre-warming DNS.

README.md

@@ -880,17 +880,21 @@ fine-grained audit reporting, e.g. for triggering deployment reports or
 firing a JSON webhook. These variables include:
 - `MRSK_RECORDED_AT` - UTC timestamp in ISO 8601 format, e.g. `2023-04-14T17:07:31Z`
 - `MRSK_PERFORMER` - the local user performing the command (from `whoami`)
-- `MRSK_MESSAGE` - the full audit message, e.g. "Deployed app@150b24f"
-- `MRSK_SERVICE_VERSION` - an abbreviated version (for use in messages)
+- `MRSK_SERVICE_VERSION` - an abbreviated service and version for use in messages, e.g. app@150b24f
+- `MRSK_VERSION` - an full version being deployed
 - `MRSK_DESTINATION` - optional: destination, e.g. "staging"
+- `MRSK_HOSTS` - a comma separated list of the hosts targeted by the command
 - `MRSK_ROLE` - optional: role targeted, e.g. "web"
 
-There are two hooks:
+There are three hooks:
 
-1. pre-build
+1. pre-connect
+Called before taking the deploy lock. For checks that need to run before connecting to remote hosts - e.g. DNS warming.
+
+2. pre-build
 Used for pre-build checks - e.g. there are no uncommitted changes or that CI has passed.
 
-2. post-deploy - run after a deploy, redeploy or rollback
+3. post-deploy - run after a deploy, redeploy or rollback
 
 This hook is also passed a `MRSK_RUNTIME` env variable.
 

lib/mrsk/cli/base.rb

@@ -76,6 +76,8 @@ module Mrsk::Cli
         if MRSK.holding_lock?
           yield
         else
+          run_hook "pre-connect"
+
           acquire_lock
 
           begin
@@ -135,7 +137,7 @@ module Mrsk::Cli
         if !options[:skip_hooks] && MRSK.hook.hook_exists?(hook)
           say "Running the #{hook} hook...", :magenta
           run_locally do
-            MRSK.with_verbosity(:debug) { execute *MRSK.hook.run(hook, **details) }
+            MRSK.with_verbosity(:debug) { execute *MRSK.hook.run(hook, **details, hosts: MRSK.hosts.join(",")) }
           rescue SSHKit::Command::Failed
             raise HookError.new("Hook `#{hook}` failed")
           end

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

@@ -12,6 +12,8 @@
 # MRSK_RECORDED_AT
 # MRSK_PERFORMER
 # MRSK_VERSION
+# MRSK_HOSTS
+# MRSK_ROLE (if set)
 # MRSK_DESTINATION (if set)
 # MRSK_RUNTIME
 

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

@@ -12,6 +12,8 @@
 # MRSK_RECORDED_AT
 # MRSK_PERFORMER
 # MRSK_VERSION
+# MRSK_HOSTS
+# MRSK_ROLE (if set)
 # MRSK_DESTINATION (if set)
 
 if [ -n "$(git status --porcelain)" ]; then

lib/mrsk/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:
+# MRSK_RECORDED_AT
+# MRSK_PERFORMER
+# MRSK_VERSION
+# MRSK_HOSTS
+# MRSK_ROLE (if set)
+# MRSK_DESTINATION (if set)
+# MRSK_RUNTIME
+
+hosts = ENV["MRSK_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 ]

test/cli/main_test.rb

@@ -23,6 +23,7 @@ class CliMainTest < CliTestCase
     Mrsk::Commands::Hook.any_instance.stubs(:hook_exists?).returns(true)
 
     run_command("deploy").tap do |output|
+      assert_match /Running the pre-connect hook.../, output
       assert_match /Log into image registry/, output
       assert_match /Build and push app image/, output
       assert_match /Ensure Traefik is running/, output

test/integration/docker/deployer/app/.mrsk/hooks/pre-connect

@@ -0,0 +1,8 @@
+#!/bin/sh
+
+echo "About to lock..."
+if [ "$MRSK_HOSTS" != "vm1,vm2" ]; then
+  echo "Expected hosts to be 'vm1,vm2', got $MRSK_HOSTS"
+  exit 1
+fi
+mkdir -p /tmp/${TEST_ID} && touch /tmp/${TEST_ID}/pre-connect

test/integration/main_test.rb

@@ -8,16 +8,16 @@ class MainTest < IntegrationTest
 
     mrsk :deploy
     assert_app_is_up version: first_version
-    assert_hooks_ran "pre-build", "post-deploy"
+    assert_hooks_ran "pre-connect", "pre-build", "post-deploy"
 
     second_version = update_app_rev
 
     mrsk :redeploy
     assert_app_is_up version: second_version
-    assert_hooks_ran "pre-build", "post-deploy"
+    assert_hooks_ran "pre-connect", "pre-build", "post-deploy"
 
     mrsk :rollback, first_version
-    assert_hooks_ran "post-deploy"
+    assert_hooks_ran "pre-connect", "post-deploy"
     assert_app_is_up version: first_version
 
     details = mrsk :details, capture: true