Validate the build image

lib/kamal/cli/build.rb

@@ -50,6 +50,7 @@ def pull
         execute *KAMAL.auditor.record("Pulled image with version #{KAMAL.config.version}"), verbosity: :debug
         execute *KAMAL.builder.clean, raise_on_non_zero_exit: false
         execute *KAMAL.builder.pull
+        execute *KAMAL.builder.validate_image
       end
     end
   end

lib/kamal/commands/builder.rb

@@ -1,7 +1,7 @@
 require "active_support/core_ext/string/filters"
 
 class Kamal::Commands::Builder < Kamal::Commands::Base
-  delegate :create, :remove, :push, :clean, :pull, :info, to: :target
+  delegate :create, :remove, :push, :clean, :pull, :info, :validate_image, to: :target
 
   def name
     target.class.to_s.remove("Kamal::Commands::Builder::").underscore.inquiry

lib/kamal/commands/builder/base.rb

@@ -21,6 +21,12 @@ def build_context
     config.builder.context
   end
 
+  def validate_image
+    pipe \
+      docker(:inspect, "-f", "'{{ .Config.Labels.service }}'", config.absolute_image),
+      [:grep, "-x", config.service, "||", "(echo \"Image #{config.absolute_image} is missing the `service` label\" && exit 1)"]
+  end
+
 
   private
     def build_tags

test/cli/build_test.rb

@@ -57,6 +57,7 @@ class CliBuildTest < CliTestCase
     run_command("pull").tap do |output|
       assert_match /docker image rm --force dhh\/app:999/, output
       assert_match /docker pull dhh\/app:999/, output
+      assert_match "docker inspect -f '{{ .Config.Labels.service }}' dhh/app:999 | grep -x app || (echo \"Image dhh/app:999 is missing the `service` label\" && exit 1)", output
     end
   end
 

test/commands/builder_test.rb

@@ -103,6 +103,10 @@ class CommandsBuilderTest < ActiveSupport::TestCase
       builder.push.join(" ")
   end
 
+  test "validate image" do
+    assert_equal "docker inspect -f '{{ .Config.Labels.service }}' dhh/app:123 | grep -x app || (echo \"Image dhh/app:123 is missing the `service` label\" && exit 1)", new_builder_command.validate_image.join(" ")
+  end
+
   private
     def new_builder_command(additional_config = {})
       Kamal::Commands::Builder.new(Kamal::Configuration.new(@config.merge(additional_config), version: "123"))