remove tag/repository config, create digest file

a repository name and tag aren't necessary for building an image, and
baking them into the image kind of feels like a legacy practice. the OCI
format has no place for the repository to be stored.

in order to continue supporting 'docker load' and identifying the loaded
image, we can instead just write the image's digest to a separate file
in the output. this digest can then be tagged to give it a name:

    docker load -i image.tar
    docker tag $(cat digest) my-name

this feels like a much cleaner split: repository/tag naming is a concern
of pushing to a registry, not of image building, so it should be limited
to the registry-pushing resource (i.e. registry-image) instead of having
to configure it in both.

Signed-off-by: Alex Suraci <[email protected]>

Author: vito

ci/tasks/build-image.yml

@@ -15,7 +15,6 @@ outputs:
 - name: image
 
 params:
-  REPOSITORY: concourse/builder-task
   CONTEXT: builder-task
 
 run:

integration_test.go

@@ -27,9 +27,7 @@ func (s *TaskSuite) SetupTest() {
 
 	s.req = task.Request{
 		ResponsePath: filepath.Join(s.outputsDir, "response.json"),
-		Config: task.Config{
-			Repository: "builder-task-test",
-		},
+		Config:       task.Config{},
 	}
 }
 
@@ -38,18 +36,23 @@ func (s *TaskSuite) TearDownTest() {
 	s.NoError(err)
 }
 
-func (s *TaskSuite) TestMissingRepositoryValidation() {
-	s.req.Config.Repository = ""
+func (s *TaskSuite) TestBasicBuild() {
+	s.req.Config.ContextDir = "testdata/basic"
 
 	_, err := task.Build(s.outputsDir, s.req)
-	s.EqualError(err, "config: repository must be specified")
+	s.NoError(err)
 }
 
-func (s *TaskSuite) TestBasicBuild() {
-	s.req.Config.ContextDir = "testdata/basic"
+func (s *TaskSuite) TestDigestFile() {
+	s.req.Config.ContextDir = "testdata/digest"
 
 	_, err := task.Build(s.outputsDir, s.req)
 	s.NoError(err)
+
+	digest, err := ioutil.ReadFile(s.imagePath("digest"))
+	s.NoError(err)
+
+	s.Equal(string(digest), "sha256:725c9a9e7bbd75b2081c0ca92788a4d29d4d728e4efeec52a1da5f91a3d600b8")
 }
 
 func (s *TaskSuite) TestDockerfilePath() {

task.go

@@ -53,7 +53,8 @@ func Build(outputsDir string, req Request) (Response, error) {
 		return Response{}, errors.Wrap(err, "spawn buildkitd")
 	}
 
-	ociImagePath := filepath.Join(imageDir, "image.tar")
+	imagePath := filepath.Join(imageDir, "image.tar")
+	digestPath := filepath.Join(imageDir, "digest")
 
 	dockerfileDir := filepath.Dir(cfg.DockerfilePath)
 	dockerfileName := filepath.Base(cfg.DockerfilePath)
@@ -65,7 +66,7 @@ func Build(outputsDir string, req Request) (Response, error) {
 		"--local", "dockerfile=" + dockerfileDir,
 		"--opt", "filename=" + dockerfileName,
 		"--export-cache", "type=local,mode=min,dest=" + cacheDir,
-		"--output", "type=docker,dest=" + ociImagePath,
+		"--output", "type=docker,dest=" + imagePath,
 	}
 
 	if _, err := os.Stat(filepath.Join(cacheDir, "index.json")); err == nil {
@@ -95,8 +96,23 @@ func Build(outputsDir string, req Request) (Response, error) {
 		return Response{}, errors.Wrap(err, "build")
 	}
 
+	image, err := tarball.ImageFromPath(imagePath, nil)
+	if err != nil {
+		return Response{}, errors.Wrap(err, "open oci image")
+	}
+
+	manifest, err := image.Manifest()
+	if err != nil {
+		return Response{}, errors.Wrap(err, "get image digest")
+	}
+
+	err = ioutil.WriteFile(digestPath, []byte(manifest.Config.Digest.String()), 0644)
+	if err != nil {
+		return Response{}, errors.Wrap(err, "write digest")
+	}
+
 	if req.Config.UnpackRootfs {
-		err = unpackRootfs(imageDir, ociImagePath, cfg)
+		err = unpackRootfs(imageDir, image, cfg)
 		if err != nil {
 			return Response{}, errors.Wrap(err, "unpack rootfs")
 		}
@@ -105,18 +121,13 @@ func Build(outputsDir string, req Request) (Response, error) {
 	return res, nil
 }
 
-func unpackRootfs(dest string, ociImagePath string, cfg Config) error {
+func unpackRootfs(dest string, image v1.Image, cfg Config) error {
 	rootfsDir := filepath.Join(dest, "rootfs")
 	metadataPath := filepath.Join(dest, "metadata.json")
 
-	image, err := tarball.ImageFromPath(ociImagePath, nil)
-	if err != nil {
-		return errors.Wrap(err, "open oci image")
-	}
-
 	logrus.Info("unpacking image")
 
-	err = unpackImage(rootfsDir, image, cfg.Debug)
+	err := unpackImage(rootfsDir, image, cfg.Debug)
 	if err != nil {
 		return errors.Wrap(err, "unpack image")
 	}
@@ -167,10 +178,6 @@ func writeImageMetadata(metadataPath string, image v1.Image) error {
 }
 
 func sanitize(cfg *Config) error {
-	if cfg.Repository == "" {
-		return errors.New("repository must be specified")
-	}
-
 	if cfg.ContextDir == "" {
 		cfg.ContextDir = "."
 	}
@@ -179,17 +186,6 @@ func sanitize(cfg *Config) error {
 		cfg.DockerfilePath = filepath.Join(cfg.ContextDir, "Dockerfile")
 	}
 
-	if cfg.TagFile != "" {
-		target, err := ioutil.ReadFile(cfg.TagFile)
-		if err != nil {
-			return errors.Wrap(err, "read target file")
-		}
-
-		cfg.Tag = strings.TrimSpace(string(target))
-	} else if cfg.Tag == "" {
-		cfg.Tag = "latest"
-	}
-
 	if cfg.TargetFile != "" {
 		target, err := ioutil.ReadFile(cfg.TargetFile)
 		if err != nil {

testdata/basic/Dockerfile

@@ -1 +1,2 @@
 FROM scratch
+COPY Dockerfile /

testdata/digest/Dockerfile

@@ -0,0 +1,4 @@
+FROM scratch
+
+# nothing; just need an image with a fixed digest
+COPY Dockerfile /

testdata/dockerfile-path/hello.Dockerfile

@@ -1 +1,2 @@
-FROM scratch
+FROM busybox
+RUN true

types.go

@@ -44,13 +44,8 @@ type Response struct {
 // For now, and for backwards-compatibility, we will also support taking values
 // from task params (i.e. env), hence the use of `envconfig:`.
 type Config struct {
-	Repository string `json:"repository"`
-
 	Debug bool `json:"debug" envconfig:"optional"`
 
-	Tag     string `json:"tag"      envconfig:"optional"`
-	TagFile string `json:"tag_file" envconfig:"optional"`
-
 	ContextDir     string `json:"context"              envconfig:"CONTEXT,optional"`
 	DockerfilePath string `json:"dockerfile,omitempty" envconfig:"DOCKERFILE,optional"`
 
@@ -66,10 +61,6 @@ type Config struct {
 	UnpackRootfs bool `json:"unpack_rootfs" envconfig:"optional"`
 }
 
-func (cfg Config) ImageName() string {
-	return cfg.Repository + ":" + cfg.Tag
-}
-
 // ImageMetadata is the schema written to manifest.json when producing the
 // legacy Concourse image format (rootfs/..., metadata.json).
 type ImageMetadata struct {