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.

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 ]