Zero downtime deployment with cord file

lib/kamal/cli/app.rb

@@ -18,8 +18,9 @@ def boot
             roles.each do |role|
               app = KAMAL.app(role: role)
               auditor = KAMAL.auditor(role: role)
+              role_config = KAMAL.config.role(role)
 
-              if capture_with_info(*app.container_id_for_version(version, only_running: true), raise_on_non_zero_exit: false).present?
+              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
@@ -29,11 +30,25 @@ def boot
               execute *auditor.record("Booted app version #{version}"), verbosity: :debug
 
               old_version = capture_with_info(*app.current_running_version, raise_on_non_zero_exit: false).strip
-              execute *app.start_or_run(hostname: "#{host}-#{SecureRandom.hex(6)}")
+
+              if role_config.uses_cord?
+                execute *app.tie_cord(role_config.cord_host_file)
+              end
+
+              execute *app.run(hostname: "#{host}-#{SecureRandom.hex(6)}")
 
               Kamal::Utils::HealthcheckPoller.wait_for_healthy(pause_after_ready: true) { capture_with_info(*app.status(version: version)) }
 
-              execute *app.stop(version: old_version), raise_on_non_zero_exit: false if old_version.present?
+              if old_version.present?
+                if role_config.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::Utils::HealthcheckPoller.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
+              end
             end
           end
         end

lib/kamal/commands/app.rb

@@ -1,34 +1,29 @@
 class Kamal::Commands::App < Kamal::Commands::Base
   ACTIVE_DOCKER_STATUSES = [ :running, :restarting ]
 
-  attr_reader :role
+  attr_reader :role, :role_config
 
   def initialize(config, role: nil)
     super(config)
     @role = role
-  end
-
-  def start_or_run(hostname: nil)
-    combine start, run(hostname: hostname), by: "||"
+    @role_config = config.role(self.role)
   end
 
   def run(hostname: nil)
-    role = config.role(self.role)
-
     docker :run,
       "--detach",
       "--restart unless-stopped",
       "--name", container_name,
       *(["--hostname", hostname] if hostname),
       "-e", "KAMAL_CONTAINER_NAME=\"#{container_name}\"",
-      *role.env_args,
-      *role.health_check_args,
+      *role_config.env_args,
+      *role_config.health_check_args,
       *config.logging_args,
       *config.volume_args,
-      *role.label_args,
-      *role.option_args,
+      *role_config.label_args,
+      *role_config.option_args,
       config.absolute_image,
-      role.cmd
+      role_config.cmd
   end
 
   def start
@@ -76,14 +71,12 @@ def execute_in_existing_container(*command, interactive: false)
   end
 
   def execute_in_new_container(*command, interactive: false)
-    role = config.role(self.role)
-
     docker :run,
       ("-it" if interactive),
       "--rm",
-      *role&.env_args,
+      *role_config&.env_args,
       *config.volume_args,
-      *role&.option_args,
+      *role_config&.option_args,
       config.absolute_image,
       *command
   end
@@ -112,7 +105,7 @@ def current_running_version
   def list_versions(*docker_args, statuses: nil)
     pipe \
       docker(:ps, *filter_args(statuses: statuses), *docker_args, "--format", '"{{.Names}}"'),
-      %(while read line; do echo ${line##{service_role_dest}-}; done) # Extract SHA from "service-role-dest-SHA"
+      %(while read line; do echo ${line##{role_config.full_name}-}; done) # Extract SHA from "service-role-dest-SHA"
   end
 
   def list_containers
@@ -150,16 +143,30 @@ def tag_current_as_latest
   end
 
   def make_env_directory
-    make_directory config.role(role).host_env_directory
+    make_directory role_config.host_env_directory
   end
 
   def remove_env_file
-    [:rm, "-f", config.role(role).host_env_file_path]
+    [:rm, "-f", role_config.host_env_file_path]
+  end
+
+  def cord(version:)
+    pipe \
+      docker(:inspect, "-f '{{ range .Mounts }}{{ .Source }} {{ .Destination }} {{ end }}'", container_name(version)),
+      [:awk, "'$2 == \"#{role_config.cord_container_directory}\" {print $1}'"]
+  end
+
+  def tie_cord(cord)
+    create_empty_file(cord)
+  end
+
+  def cut_cord(cord)
+    remove_directory(cord)
   end
 
   private
     def container_name(version = nil)
-      [ config.service, role, config.destination, version || config.version ].compact.join("-")
+      [ role_config.full_name, version || config.version ].compact.join("-")
     end
 
     def filter_args(statuses: nil)

lib/kamal/commands/base.rb

@@ -34,6 +34,10 @@ def make_directory(path)
       [ :mkdir, "-p", path ]
     end
 
+    def remove_directory(path)
+      [ :rm, "-r", path ]
+    end
+
     private
       def combine(*commands, by: "&&")
         commands
@@ -69,5 +73,11 @@ def docker(*args)
       def tags(**details)
         Kamal::Tags.from_config(config, **details)
       end
+
+      def create_empty_file(file)
+        chain \
+          make_directory_for(file),
+          [:touch, file]
+      end
   end
 end

lib/kamal/commands/healthcheck.rb

@@ -10,7 +10,7 @@ def run
       "--label", "service=#{container_name}",
       "-e", "KAMAL_CONTAINER_NAME=\"#{container_name}\"",
       *web.env_args,
-      *web.health_check_args,
+      *web.health_check_args(cord: false),
       *config.volume_args,
       *web.option_args,
       config.absolute_image,

lib/kamal/configuration.rb

@@ -61,6 +61,14 @@ 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 roles
     @roles ||= role_names.collect { |role_name| Role.new(role_name, config: self) }
@@ -141,7 +149,7 @@ def sshkit
 
 
   def healthcheck
-    { "path" => "/up", "port" => 3000, "max_attempts" => 7, "exposed_port" => 3999 }.merge(raw_config.healthcheck || {})
+    { "path" => "/up", "port" => 3000, "max_attempts" => 7, "exposed_port" => 3999, "cord" => "/tmp/kamal-cord" }.merge(raw_config.healthcheck || {})
   end
 
   def readiness_delay
@@ -199,6 +207,10 @@ def host_env_directory
     "#{run_directory}/env"
   end
 
+  def run_id
+    @run_id ||= SecureRandom.hex(16)
+  end
+
   private
     # Will raise ArgumentError if any required config keys are missing
     def ensure_required_keys_present

lib/kamal/configuration/role.rb

@@ -1,4 +1,5 @@
 class Kamal::Configuration::Role
+  CORD_FILE = "cord"
   delegate :argumentize, :env_file_with_secrets, :optionize, to: Kamal::Utils
 
   attr_accessor :name
@@ -47,28 +48,52 @@ def env_args
     argumentize "--env-file", host_env_file_path
   end
 
-  def health_check_args
+  def health_check_args(cord: true)
     if health_check_cmd.present?
-      optionize({ "health-cmd" => health_check_cmd, "health-interval" => health_check_interval })
+      if cord && uses_cord?
+        optionize({ "health-cmd" => health_check_cmd_with_cord, "health-interval" => health_check_interval })
+          .concat(["--volume", "#{cord_host_directory}:#{cord_container_directory}"])
+      else
+        optionize({ "health-cmd" => health_check_cmd, "health-interval" => health_check_interval })
+      end
     else
       []
     end
   end
 
   def health_check_cmd
-    options = specializations["healthcheck"] || {}
-    options = config.healthcheck.merge(options) if running_traefik?
+    health_check_options["cmd"] || http_health_check(port: health_check_options["port"], path: health_check_options["path"])
+  end
 
-    options["cmd"] || http_health_check(port: options["port"], path: options["path"])
+  def health_check_cmd_with_cord
+    "(#{health_check_cmd}) && (stat #{cord_container_file} > /dev/null || exit 1)"
   end
 
   def health_check_interval
-    options = specializations["healthcheck"] || {}
-    options = config.healthcheck.merge(options) if running_traefik?
+    health_check_options["interval"] || "1s"
+  end
+
+  def uses_cord?
+    running_traefik? && cord_container_directory.present? && health_check_cmd.present?
+  end
+
+  def cord_host_directory
+    File.join config.run_directory_as_docker_volume, "cords", [full_name, config.run_id].join("-")
+  end
+
+  def cord_host_file
+    File.join cord_host_directory, CORD_FILE
+  end
+
+  def cord_container_directory
+    health_check_options.fetch("cord", nil)
+  end
 
-    options["interval"] || "1s"
+  def cord_container_file
+    File.join cord_container_directory, CORD_FILE
   end
 
+
   def cmd
     specializations["cmd"]
   end
@@ -85,6 +110,10 @@ def running_traefik?
     name.web? || specializations["traefik"]
   end
 
+  def full_name
+    [ config.service, name, config.destination ].compact.join("-")
+  end
+
   private
     attr_accessor :config
 
@@ -164,4 +193,12 @@ def merged_env_with_secrets
     def http_health_check(port:, path:)
       "curl -f #{URI.join("http://localhost:#{port}", path)} || exit 1" if path.present? || port.present?
     end
+
+    def health_check_options
+      @health_check_options ||= begin
+        options = specializations["healthcheck"] || {}
+        options = config.healthcheck.merge(options) if running_traefik?
+        options
+      end
+    end
 end

lib/kamal/utils/healthcheck_poller.rb

@@ -1,5 +1,5 @@
 class Kamal::Utils::HealthcheckPoller
-  TRAEFIK_HEALTHY_DELAY = 2
+  TRAEFIK_UPDATE_DELAY = 2
 
   class HealthcheckError < StandardError; end
 
@@ -11,7 +11,7 @@ def wait_for_healthy(pause_after_ready: false, &block)
       begin
         case status = block.call
         when "healthy"
-          sleep TRAEFIK_HEALTHY_DELAY if pause_after_ready
+          sleep TRAEFIK_UPDATE_DELAY if pause_after_ready
         when "running" # No health check configured
           sleep KAMAL.config.readiness_delay if pause_after_ready
         else
@@ -31,6 +31,31 @@ def wait_for_healthy(pause_after_ready: false, &block)
       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 HealthcheckError, "container not unhealthy (#{status})"
+        end
+      rescue HealthcheckError => 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)

test/cli/app_test.rb

@@ -11,10 +11,11 @@ class CliAppTest < CliTestCase
   end
 
   test "boot will rename if same version is already running" do
+    Object.any_instance.stubs(:sleep)
     run_command("details") # Preheat Kamal const
 
     SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
-      .with(:docker, :container, :ls, "--filter", "name=^app-web-latest$", "--quiet", raise_on_non_zero_exit: false)
+      .with(:docker, :container, :ls, "--all", "--filter", "name=^app-web-latest$", "--quiet", raise_on_non_zero_exit: false)
       .returns("12345678") # running version
 
     SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
@@ -25,6 +26,14 @@ class CliAppTest < CliTestCase
       .with(:docker, :ps, "--filter", "label=service=app", "--filter", "label=role=web", "--filter", "status=running", "--filter", "status=restarting", "--latest", "--format", "\"{{.Names}}\"", "|", "while read line; do echo ${line#app-web-}; done", raise_on_non_zero_exit: false)
       .returns("123") # old version
 
+    SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+      .with(:docker, :inspect, "-f '{{ range .Mounts }}{{ .Source }} {{ .Destination }} {{ end }}'", "app-web-123", "|", :awk, "'$2 == \"/tmp/kamal-cord\" {print $1}'", :raise_on_non_zero_exit => false)
+      .returns("cordfile") # old version
+
+    SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+      .with(:docker, :container, :ls, "--all", "--filter", "name=^app-web-123$", "--quiet", "|", :xargs, :docker, :inspect, "--format", "'{{if .State.Health}}{{.State.Health.Status}}{{else}}{{.State.Status}}{{end}}'")
+      .returns("unhealthy") # old version unhealthy
+
     run_command("boot").tap do |output|
       assert_match /Renaming container .* to .* as already deployed on 1.1.1.1/, output # Rename
       assert_match /docker rename app-web-latest app-web-latest_replaced_[0-9a-f]{16}/, output
@@ -180,10 +189,16 @@ def run_command(*command, config: :with_accessories)
     end
 
     def stub_running
+      Object.any_instance.stubs(:sleep)
+
       SSHKit::Backend::Abstract.any_instance.stubs(:capture_with_info).returns("123") # old version
 
       SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
         .with(:docker, :container, :ls, "--all", "--filter", "name=^app-web-latest$", "--quiet", "|", :xargs, :docker, :inspect, "--format", "'{{if .State.Health}}{{.State.Health.Status}}{{else}}{{.State.Status}}{{end}}'")
         .returns("running") # health check
+
+      SSHKit::Backend::Abstract.any_instance.expects(:capture_with_info)
+        .with(:docker, :container, :ls, "--all", "--filter", "name=^app-web-123$", "--quiet", "|", :xargs, :docker, :inspect, "--format", "'{{if .State.Health}}{{.State.Health.Status}}{{else}}{{.State.Status}}{{end}}'")
+        .returns("unhealthy") # health check
     end
 end

test/cli/healthcheck_test.rb

@@ -6,6 +6,7 @@ class CliHealthcheckTest < CliTestCase
     Thread.report_on_exception = false
 
     Kamal::Utils::HealthcheckPoller.stubs(:sleep) # No sleeping when retrying
+    Kamal::Configuration.any_instance.stubs(:run_id).returns("12345678901234567890123456789012")
 
     SSHKit::Backend::Abstract.any_instance.stubs(:execute)
       .with(:docker, :container, :ls, "--all", "--filter", "name=^healthcheck-app-999$", "--quiet", "|", :xargs, :docker, :stop, raise_on_non_zero_exit: false)