Add pack option to the builder options for cloud native buildpacks

lib/kamal/commands/base.rb

@@ -77,6 +77,10 @@ def docker(*args)
         args.compact.unshift :docker
       end
 
+      def pack(*args)
+        args.compact.unshift :pack
+      end
+
       def git(*args, path: nil)
         [ :git, *([ "-C", path ] if path), *args.compact ]
       end

lib/kamal/commands/builder.rb

@@ -18,6 +18,8 @@ def target
         else
           native_remote
         end
+      elsif config.builder.pack?
+        pack
       else
         multiarch
       end
@@ -50,6 +52,9 @@ def multiarch_remote
     @multiarch_remote ||= Kamal::Commands::Builder::Multiarch::Remote.new(config)
   end
 
+  def pack
+    @pack ||= Kamal::Commands::Builder::Native::Pack.new(config)
+  end
 
   def ensure_local_dependencies_installed
     if name.native?

lib/kamal/commands/builder/base.rb

@@ -5,7 +5,7 @@ class BuilderError < StandardError; end
   ENDPOINT_DOCKER_HOST_INSPECT = "'{{.Endpoints.docker.Host}}'"
 
   delegate :argumentize, to: Kamal::Utils
-  delegate :args, :secrets, :dockerfile, :target, :local_arch, :local_host, :remote_arch, :remote_host, :cache_from, :cache_to, :ssh, to: :builder_config
+  delegate :args, :secrets, :dockerfile, :target, :local_arch, :local_host, :pack_arch, :pack_builder, :pack_buildpacks, :remote_arch, :remote_host, :cache_from, :cache_to, :ssh, to: :builder_config
 
   def clean
     docker :image, :rm, "--force", config.absolute_image

lib/kamal/commands/builder/native/pack.rb

@@ -0,0 +1,26 @@
+class Kamal::Commands::Builder::Native::Pack < Kamal::Commands::Builder::Native
+  def push
+    combine \
+      pack(:build,
+        config.absolute_image,
+        "--platform", platform,
+        "--builder", pack_builder,
+        buildpacks,
+        "-t", config.absolute_image,
+        "-t", config.latest_image,
+        "--env", "BP_IMAGE_LABELS=service=#{config.service}",
+        secrets.map { |secret| ["--env", Kamal::Utils.sensitive(ENV[secret])] },
+        "--path", build_context),
+      docker(:push, config.absolute_image),
+      docker(:push, config.latest_image)
+  end
+
+  private
+    def platform
+      "linux/#{pack_arch}"
+    end
+
+    def buildpacks
+      (pack_buildpacks << "paketo-buildpacks/image-labels").map { |buildpack| ["--buildpack", buildpack] }
+    end
+end

lib/kamal/configuration/builder.rb

@@ -35,6 +35,10 @@ def cached?
     !!builder_config["cache"]
   end
 
+  def pack?
+    !!builder_config["pack"]
+  end
+
   def args
     builder_config["args"] || {}
   end
@@ -63,6 +67,18 @@ def local_host
     builder_config["local"]["host"] if local?
   end
 
+  def pack_arch
+    builder_config["pack"]["arch"] if pack?
+  end
+
+  def pack_builder
+    builder_config["pack"]["builder"] if pack?
+  end
+
+  def pack_buildpacks
+    builder_config["pack"]["buildpacks"] if pack?
+  end
+
   def remote_arch
     builder_config["remote"]["arch"] if remote?
   end

lib/kamal/configuration/docs/builder.yml

@@ -37,6 +37,16 @@ builder:
     arch: arm64
     host: ssh://docker@docker-builder
 
+  # Buildpack configuration
+  #
+  # The build configuration for using pack to build a Cloud Native Buildpack image.
+  pack:
+    builder: heroku/builder:24
+    arch: amd64
+    buildpacks:
+    - heroku/ruby
+    - heroku/procfile
+
   # Builder cache
   #
   # The type must be either 'gha' or 'registry'

test/commands/builder_test.rb

@@ -53,6 +53,14 @@ class CommandsBuilderTest < ActiveSupport::TestCase
       builder.push.join(" ")
   end
 
+  test "target pack when pack is set" do
+    builder = new_builder_command(builder: { "pack" => { "arch" => "amd64" , "builder" => "heroku/builder:24", "buildpacks" => [ "heroku/ruby", "heroku/procfile" ] }})
+    assert_equal "native/pack", builder.name
+    assert_equal \
+      "pack build dhh/app:123 --platform linux/amd64 --builder heroku/builder:24 --buildpack heroku/ruby --buildpack heroku/procfile --buildpack paketo-buildpacks/image-labels -t dhh/app:123 -t dhh/app:latest --env BP_IMAGE_LABELS=service=app --path . && docker push dhh/app:123 && docker push dhh/app:latest",
+      builder.push.join(" ")
+  end
+
   test "build args" do
     builder = new_builder_command(builder: { "args" => { "a" => 1, "b" => 2 } })
     assert_equal \

test/configuration/builder_test.rb

@@ -32,6 +32,24 @@ class ConfigurationBuilderTest < ActiveSupport::TestCase
     assert_equal false, config.builder.remote?
   end
 
+  test "pack?" do
+    refute config.builder.pack?
+  end
+
+  test "pack? with pack builder" do
+    @deploy[:builder] = { "pack" => {"builder" => "heroku/builder:24"} }
+
+    assert config.builder.pack?
+  end
+
+  test "pack details" do
+    @deploy[:builder] = { "pack" => {"arch" => "amd64", "builder" => "heroku/builder:24", "buildpacks" => ["heroku/ruby", "heroku/procfile"]} }
+
+    assert_equal "amd64", config.builder.pack_arch
+    assert_equal "heroku/builder:24", config.builder.pack_builder
+    assert_equal ["heroku/ruby", "heroku/procfile"], config.builder.pack_buildpacks
+  end
+
   test "remote_arch" do
     assert_nil config.builder.remote_arch
   end