Extract app boot steps

The Kamal::Cli::App#boot has a lot to do, so extract the steps to make
things clearer.

lib/kamal/cli/app.rb

@@ -7,56 +7,19 @@ class Kamal::Cli::App < Kamal::Cli::Base
         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
             execute *KAMAL.auditor.record("Tagging #{KAMAL.config.absolute_image} as the latest image"), verbosity: :debug
             execute *KAMAL.app.tag_current_image_as_latest
 
             KAMAL.roles_on(host).each do |role|
-              app = KAMAL.app(role: role)
+              Kamal::Cli::App::PrepareAssets.new(host, role, self).run
-
-              if role.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
           end
 
           on(KAMAL.hosts, **KAMAL.boot_strategy) do |host|
             KAMAL.roles_on(host).each do |role|
-              app = KAMAL.app(role: role)
+              Kamal::Cli::App::Boot.new(host, role, version, self).run
-              auditor = KAMAL.auditor(role: role)
-
-              if capture_with_info(*app.container_id_for_version(version), raise_on_non_zero_exit: false).present?
-                tmp_version = "#{version}_replaced_#{SecureRandom.hex(8)}"
-                info "Renaming container #{version} to #{tmp_version} as already deployed on #{host}"
-                execute *auditor.record("Renaming container #{version} to #{tmp_version}"), verbosity: :debug
-                execute *app.rename_container(version: version, new_version: tmp_version)
-              end
-
-              old_version = capture_with_info(*app.current_running_version, raise_on_non_zero_exit: false).strip
-
-              execute *app.tie_cord(role.cord_host_file) if role.uses_cord?
-
-              execute *auditor.record("Booted app version #{version}"), verbosity: :debug
-
-              execute *app.run(hostname: "#{host}-#{SecureRandom.hex(6)}")
-
-              Kamal::Cli::Healthcheck::Poller.wait_for_healthy(pause_after_ready: true) { capture_with_info(*app.status(version: version)) }
-
-              if old_version.present?
-                if role.uses_cord?
-                  cord = capture_with_info(*app.cord(version: old_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: old_version)) }
-                  end
-                end
-
-                execute *app.stop(version: old_version), raise_on_non_zero_exit: false
-
-                execute *app.clean_up_assets if role.assets?
-              end
             end
           end
         end

lib/kamal/cli/app/boot.rb

@@ -0,0 +1,67 @@
+class Kamal::Cli::App::Boot
+  attr_reader :host, :role, :version, :sshkit
+  delegate :execute, :capture_with_info, :info, to: :sshkit
+  delegate :uses_cord?, :assets?, to: :role
+
+  def initialize(host, role, version, sshkit)
+    @host = host
+    @role = role
+    @version = version
+    @sshkit = sshkit
+  end
+
+  def run
+    old_version = old_version_renamed_if_clashing
+
+    start_new_version
+
+    if old_version
+      stop_old_version(old_version)
+    end
+  end
+
+  private
+    def app
+      @app ||= KAMAL.app(role: role)
+    end
+
+    def auditor
+      @auditor = KAMAL.auditor(role: role)
+    end
+
+    def audit(message)
+      execute *auditor.record(message), verbosity: :debug
+    end
+
+    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?
+      execute *app.run(hostname: "#{host}-#{SecureRandom.hex(6)}")
+      Kamal::Cli::Healthcheck::Poller.wait_for_healthy(pause_after_ready: true) { capture_with_info(*app.status(version: version)) }
+    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
+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)
+    end
+end