Prune healthcheck containers

If a deployment is interrupted it could leave stale healthcheck
containers around that prevent dependent images from being pruned.

lib/kamal/cli/prune.rb

@@ -23,7 +23,8 @@ class Kamal::Cli::Prune < Kamal::Cli::Base
     mutating do
       on(KAMAL.hosts) do
         execute *KAMAL.auditor.record("Pruned containers"), verbosity: :debug
-        execute *KAMAL.prune.containers
+        execute *KAMAL.prune.app_containers
+        execute *KAMAL.prune.healthcheck_containers
       end
     end
   end

lib/kamal/commands/healthcheck.rb

@@ -7,8 +7,8 @@ class Kamal::Commands::Healthcheck < Kamal::Commands::Base
       "--detach",
       "--name", container_name_with_version,
       "--publish", "#{exposed_port}:#{config.healthcheck["port"]}",
-      "--label", "service=#{container_name}",
-      "-e", "KAMAL_CONTAINER_NAME=\"#{container_name}\"",
+      "--label", "service=#{config.healthcheck_service}",
+      "-e", "KAMAL_CONTAINER_NAME=\"#{config.healthcheck_service}\"",
       *web.env_args,
       *web.health_check_args(cord: false),
       *config.volume_args,
@@ -38,12 +38,8 @@ class Kamal::Commands::Healthcheck < Kamal::Commands::Base
   end
 
   private
-    def container_name
-      [ "healthcheck", config.service, config.destination ].compact.join("-")
-    end
-
     def container_name_with_version
-      "#{container_name}-#{config.version}"
+      "#{config.healthcheck_service}-#{config.version}"
     end
 
     def container_id

lib/kamal/commands/prune.rb

@@ -13,13 +13,17 @@ class Kamal::Commands::Prune < Kamal::Commands::Base
       "while read image tag; do docker rmi $tag; done"
   end
 
-  def containers(keep_last: 5)
+  def app_containers(keep_last: 5)
     pipe \
       docker(:ps, "-q", "-a", *service_filter, *stopped_containers_filters),
       "tail -n +#{keep_last + 1}",
       "while read container_id; do docker rm $container_id; done"
   end
 
+  def healthcheck_containers
+    docker :container, :prune, "--force", *healthcheck_service_filter
+  end
+
   private
     def stopped_containers_filters
       [ "created", "exited", "dead" ].flat_map { |status| ["--filter", "status=#{status}"] }
@@ -35,4 +39,8 @@ class Kamal::Commands::Prune < Kamal::Commands::Base
     def service_filter
       [ "--filter", "label=service=#{config.service}" ]
     end
-end
+
+    def healthcheck_service_filter
+      [ "--filter", "label=service=#{config.healthcheck_service}" ]
+    end
+  end

lib/kamal/configuration.rb

@@ -152,6 +152,10 @@ class Kamal::Configuration
     { "path" => "/up", "port" => 3000, "max_attempts" => 7, "exposed_port" => 3999, "cord" => "/tmp/kamal-cord" }.merge(raw_config.healthcheck || {})
   end
 
+  def healthcheck_service
+    [ "healthcheck", service, destination ].compact.join("-")
+  end
+
   def readiness_delay
     raw_config.readiness_delay || 7
   end