Make `FROM scratch` a special cased 'no-base' spec

There has been a lot of discussion (issues 4242 and 5262) about making
`FROM scratch` either a special case or making `FROM` optional, implying
starting from an empty file system.

This patch makes the build command `FROM scratch` special cased from now on
and if used does not pull/set the the initial layer of the build to the ancient
image ID (511136ea..) but instead marks the build as having no base image. The
next command in the dockerfile will create an image with a parent image ID of "".
This means every image ever can now use one fewer layer!

This also makes the image name `scratch` a reserved name by the TagStore. You
will not be able to tag an image with this name from now on. If any users
currently have an image tagged as `scratch`, they will still be able to use that
image, but will not be able to tag a new image with that name.

Goodbye '511136ea3c5a64f264b78b5433614aec563103b4d4702f3ba7d4d2698e22c158',
it was nice knowing you.

Fixes #4242

Docker-DCO-1.1-Signed-off-by: Josh Hawn <josh.hawn@docker.com> (github: jlhawn)

api/client/commands.go

@@ -1696,7 +1696,12 @@ func (cli *DockerCli) CmdPs(args ...string) error {
 
 		ports.ReadListFrom([]byte(out.Get("Ports")))
 
-		fmt.Fprintf(w, "%s\t%s\t%s\t%s ago\t%s\t%s\t%s\t", outID, out.Get("Image"), outCommand,
+		image := out.Get("Image")
+		if image == "" {
+			image = "<no image>"
+		}
+
+		fmt.Fprintf(w, "%s\t%s\t%s\t%s ago\t%s\t%s\t%s\t", outID, image, outCommand,
 			units.HumanDuration(time.Now().UTC().Sub(time.Unix(out.GetInt64("Created"), 0))),
 			out.Get("Status"), api.DisplayablePorts(ports), strings.Join(outNames, ","))
 

builder/dispatchers.go

@@ -21,6 +21,12 @@ import (
 	"github.com/docker/docker/runconfig"
 )
 
+const (
+	// NoBaseImageSpecifier is the symbol used by the FROM
+	// command to specify that no base image is to be used.
+	NoBaseImageSpecifier string = "scratch"
+)
+
 // dispatch with no layer / parsing. This is effectively not a command.
 func nullDispatch(b *Builder, args []string, attributes map[string]bool, original string) error {
 	return nil
@@ -115,6 +121,12 @@ func from(b *Builder, args []string, attributes map[string]bool, original string
 
 	name := args[0]
 
+	if name == NoBaseImageSpecifier {
+		b.image = ""
+		b.noBaseImage = true
+		return nil
+	}
+
 	image, err := b.Daemon.Repositories().LookupImage(name)
 	if b.Pull {
 		image, err = b.pullImage(name)
@@ -191,7 +203,7 @@ func workdir(b *Builder, args []string, attributes map[string]bool, original str
 // RUN [ "echo", "hi" ] # echo hi
 //
 func run(b *Builder, args []string, attributes map[string]bool, original string) error {
-	if b.image == "" {
+	if b.image == "" && !b.noBaseImage {
 		return fmt.Errorf("Please provide a source image with `from` prior to run")
 	}
 

builder/evaluator.go

@@ -110,7 +110,7 @@ type Builder struct {
 	cmdSet      bool          // indicates is CMD was set in current Dockerfile
 	context     tarsum.TarSum // the context is a tarball that is uploaded by the client
 	contextPath string        // the path of the temporary directory the local context is unpacked to (server side)
-
+	noBaseImage bool          // indicates that this build does not start from any base image, but is being built from an empty file system.
 }
 
 // Run the builder with the context. This is the lynchpin of this package. This

builder/internals.go

@@ -58,7 +58,7 @@ func (b *Builder) readContext(context io.Reader) error {
 }
 
 func (b *Builder) commit(id string, autoCmd []string, comment string) error {
-	if b.image == "" {
+	if b.image == "" && !b.noBaseImage {
 		return fmt.Errorf("Please provide a source image with `from` prior to commit")
 	}
 	b.Config.Image = b.image
@@ -513,7 +513,7 @@ func (b *Builder) probeCache() (bool, error) {
 }
 
 func (b *Builder) create() (*daemon.Container, error) {
-	if b.image == "" {
+	if b.image == "" && !b.noBaseImage {
 		return nil, fmt.Errorf("Please provide a source image with `from` prior to run")
 	}
 	b.Config.Image = b.image

daemon/commit.go

@@ -59,17 +59,17 @@ func (daemon *Daemon) Commit(container *Container, repository, tag, comment, aut
 
 	// Create a new image from the container's base layers + a new layer from container changes
 	var (
-		containerID, containerImage string
-		containerConfig             *runconfig.Config
+		containerID, parentImageID string
+		containerConfig            *runconfig.Config
 	)
 
 	if container != nil {
 		containerID = container.ID
-		containerImage = container.Image
+		parentImageID = container.ImageID
 		containerConfig = container.Config
 	}
 
-	img, err := daemon.graph.Create(rwTar, containerID, containerImage, comment, author, containerConfig, config)
+	img, err := daemon.graph.Create(rwTar, containerID, parentImageID, comment, author, containerConfig, config)
 	if err != nil {
 		return nil, err
 	}

daemon/container.go

@@ -62,8 +62,8 @@ type Container struct {
 	Path string
 	Args []string
 
-	Config *runconfig.Config
-	Image  string
+	Config  *runconfig.Config
+	ImageID string `json:"Image"`
 
 	NetworkSettings *NetworkSettings
 
@@ -186,7 +186,7 @@ func (container *Container) WriteHostConfig() error {
 
 func (container *Container) LogEvent(action string) {
 	d := container.daemon
-	if err := d.eng.Job("log", action, container.ID, d.Repositories().ImageName(container.Image)).Run(); err != nil {
+	if err := d.eng.Job("log", action, container.ID, d.Repositories().ImageName(container.ImageID)).Run(); err != nil {
 		log.Errorf("Error logging event %s for %s: %s", action, container.ID, err)
 	}
 }
@@ -786,7 +786,7 @@ func (container *Container) GetImage() (*image.Image, error) {
 	if container.daemon == nil {
 		return nil, fmt.Errorf("Can't get image of unregistered container")
 	}
-	return container.daemon.graph.Get(container.Image)
+	return container.daemon.graph.Get(container.ImageID)
 }
 
 func (container *Container) Unmount() error {

daemon/create.go

@@ -5,6 +5,7 @@ import (
 
 	"github.com/docker/docker/engine"
 	"github.com/docker/docker/graph"
+	"github.com/docker/docker/image"
 	"github.com/docker/docker/pkg/parsers"
 	"github.com/docker/docker/runconfig"
 	"github.com/docker/libcontainer/label"
@@ -68,15 +69,22 @@ func (daemon *Daemon) Create(config *runconfig.Config, hostConfig *runconfig.Hos
 	var (
 		container *Container
 		warnings  []string
+		img       *image.Image
+		imgID     string
+		err       error
 	)
 
-	img, err := daemon.repositories.LookupImage(config.Image)
-	if err != nil {
-		return nil, nil, err
-	}
-	if err := img.CheckDepth(); err != nil {
-		return nil, nil, err
+	if config.Image != "" {
+		img, err = daemon.repositories.LookupImage(config.Image)
+		if err != nil {
+			return nil, nil, err
+		}
+		if err = img.CheckDepth(); err != nil {
+			return nil, nil, err
+		}
+		imgID = img.ID
 	}
+
 	if warnings, err = daemon.mergeAndVerifyConfig(config, img); err != nil {
 		return nil, nil, err
 	}
@@ -86,13 +94,13 @@ func (daemon *Daemon) Create(config *runconfig.Config, hostConfig *runconfig.Hos
 			return nil, nil, err
 		}
 	}
-	if container, err = daemon.newContainer(name, config, img); err != nil {
+	if container, err = daemon.newContainer(name, config, imgID); err != nil {
 		return nil, nil, err
 	}
 	if err := daemon.Register(container); err != nil {
 		return nil, nil, err
 	}
-	if err := daemon.createRootfs(container, img); err != nil {
+	if err := daemon.createRootfs(container); err != nil {
 		return nil, nil, err
 	}
 	if hostConfig != nil {

daemon/daemon.go

@@ -417,10 +417,10 @@ func (daemon *Daemon) checkDeprecatedExpose(config *runconfig.Config) bool {
 
 func (daemon *Daemon) mergeAndVerifyConfig(config *runconfig.Config, img *image.Image) ([]string, error) {
 	warnings := []string{}
-	if daemon.checkDeprecatedExpose(img.Config) || daemon.checkDeprecatedExpose(config) {
+	if (img != nil && daemon.checkDeprecatedExpose(img.Config)) || daemon.checkDeprecatedExpose(config) {
 		warnings = append(warnings, "The mapping to public ports on your host via Dockerfile EXPOSE (host:port:port) has been deprecated. Use -p to publish the ports.")
 	}
-	if img.Config != nil {
+	if img != nil && img.Config != nil {
 		if err := runconfig.Merge(config, img.Config); err != nil {
 			return nil, err
 		}
@@ -557,7 +557,7 @@ func parseSecurityOpt(container *Container, config *runconfig.HostConfig) error
 	return err
 }
 
-func (daemon *Daemon) newContainer(name string, config *runconfig.Config, img *image.Image) (*Container, error) {
+func (daemon *Daemon) newContainer(name string, config *runconfig.Config, imgID string) (*Container, error) {
 	var (
 		id  string
 		err error
@@ -578,7 +578,7 @@ func (daemon *Daemon) newContainer(name string, config *runconfig.Config, img *i
 		Args:            args, //FIXME: de-duplicate from config
 		Config:          config,
 		hostConfig:      &runconfig.HostConfig{},
-		Image:           img.ID, // Always use the resolved image id
+		ImageID:         imgID,
 		NetworkSettings: &NetworkSettings{},
 		Name:            name,
 		Driver:          daemon.driver.String(),
@@ -590,14 +590,14 @@ func (daemon *Daemon) newContainer(name string, config *runconfig.Config, img *i
 	return container, err
 }
 
-func (daemon *Daemon) createRootfs(container *Container, img *image.Image) error {
+func (daemon *Daemon) createRootfs(container *Container) error {
 	// Step 1: create the container directory.
 	// This doubles as a barrier to avoid race conditions.
 	if err := os.Mkdir(container.root, 0700); err != nil {
 		return err
 	}
 	initID := fmt.Sprintf("%s-init", container.ID)
-	if err := daemon.driver.Create(initID, img.ID); err != nil {
+	if err := daemon.driver.Create(initID, container.ImageID); err != nil {
 		return err
 	}
 	initPath, err := daemon.driver.Get(initID, "")

daemon/image_delete.go

@@ -131,7 +131,7 @@ func (daemon *Daemon) DeleteImage(eng *engine.Engine, name string, imgs *engine.
 
 func (daemon *Daemon) canDeleteImage(imgID string, force bool) error {
 	for _, container := range daemon.List() {
-		parent, err := daemon.Repositories().LookupImage(container.Image)
+		parent, err := daemon.Repositories().LookupImage(container.ImageID)
 		if err != nil {
 			if daemon.Graph().IsNotExist(err) {
 				return nil

daemon/inspect.go

@@ -35,7 +35,7 @@ func (daemon *Daemon) ContainerInspect(job *engine.Job) engine.Status {
 		out.SetList("Args", container.Args)
 		out.SetJson("Config", container.Config)
 		out.SetJson("State", container.State)
-		out.SetJson("Image", container.Image)
+		out.Set("Image", container.ImageID)
 		out.SetJson("NetworkSettings", container.NetworkSettings)
 		out.Set("ResolvConfPath", container.ResolvConfPath)
 		out.Set("HostnamePath", container.HostnamePath)

daemon/list.go

@@ -116,7 +116,7 @@ func (daemon *Daemon) Containers(job *engine.Job) engine.Status {
 		out := &engine.Env{}
 		out.SetJson("Id", container.ID)
 		out.SetList("Names", names[container.ID])
-		out.SetJson("Image", daemon.Repositories().ImageName(container.Image))
+		out.SetJson("Image", daemon.Repositories().ImageName(container.ImageID))
 		if len(container.Args) > 0 {
 			args := []string{}
 			for _, arg := range container.Args {

graph/tags.go

@@ -298,6 +298,9 @@ func validateRepoName(name string) error {
 	if name == "" {
 		return fmt.Errorf("Repository name can't be empty")
 	}
+	if name == "scratch" {
+		return fmt.Errorf("'scratch' is a reserved name")
+	}
 	return nil
 }
 

integration-cli/docker_cli_events_test.go

@@ -230,9 +230,9 @@ func TestEventsRedirectStdout(t *testing.T) {
 
 func TestEventsImagePull(t *testing.T) {
 	since := time.Now().Unix()
-	pullCmd := exec.Command(dockerBinary, "pull", "scratch")
+	pullCmd := exec.Command(dockerBinary, "pull", "hello-world")
 	if out, _, err := runCommandWithOutput(pullCmd); err != nil {
-		t.Fatalf("pulling the scratch image from has failed: %s, %v", out, err)
+		t.Fatalf("pulling the hello-world image from has failed: %s, %v", out, err)
 	}
 
 	eventsCmd := exec.Command(dockerBinary, "events",
@@ -243,7 +243,7 @@ func TestEventsImagePull(t *testing.T) {
 	events := strings.Split(strings.TrimSpace(out), "\n")
 	event := strings.TrimSpace(events[len(events)-1])
 
-	if !strings.HasSuffix(event, "scratch:latest: pull") {
+	if !strings.HasSuffix(event, "hello-world:latest: pull") {
 		t.Fatalf("Missing pull event - got:%q", event)
 	}
 

integration-cli/docker_cli_inspect_test.go

@@ -7,7 +7,7 @@ import (
 )
 
 func TestInspectImage(t *testing.T) {
-	imageTest := "scratch"
+	imageTest := "emptyfs"
 	imageTestID := "511136ea3c5a64f264b78b5433614aec563103b4d4702f3ba7d4d2698e22c158"
 	imagesCmd := exec.Command(dockerBinary, "inspect", "--format='{{.Id}}'", imageTest)
 	out, exitCode, err := runCommandWithOutput(imagesCmd)

integration-cli/docker_cli_pull_test.go

@@ -9,11 +9,11 @@ import (
 
 // pulling an image from the central registry should work
 func TestPullImageFromCentralRegistry(t *testing.T) {
-	pullCmd := exec.Command(dockerBinary, "pull", "scratch")
+	pullCmd := exec.Command(dockerBinary, "pull", "hello-world")
 	if out, _, err := runCommandWithOutput(pullCmd); err != nil {
-		t.Fatalf("pulling the scratch image from the registry has failed: %s, %v", out, err)
+		t.Fatalf("pulling the hello-world image from the registry has failed: %s, %v", out, err)
 	}
-	logDone("pull - pull scratch")
+	logDone("pull - pull hello-world")
 }
 
 // pulling a non-existing image from the central registry should return a non-zero exit code

integration-cli/docker_cli_save_load_test.go

@@ -270,7 +270,7 @@ func TestSaveSingleTag(t *testing.T) {
 func TestSaveImageId(t *testing.T) {
 	repoName := "foobar-save-image-id-test"
 
-	tagCmdFinal := fmt.Sprintf("%v tag scratch:latest %v:latest", dockerBinary, repoName)
+	tagCmdFinal := fmt.Sprintf("%v tag emptyfs:latest %v:latest", dockerBinary, repoName)
 	tagCmd := exec.Command("bash", "-c", tagCmdFinal)
 	if out, _, err := runCommandWithOutput(tagCmd); err != nil {
 		t.Fatalf("failed to tag repo: %s, %v", out, err)
@@ -370,7 +370,7 @@ func TestSaveMultipleNames(t *testing.T) {
 	repoName := "foobar-save-multi-name-test"
 
 	// Make one image
-	tagCmdFinal := fmt.Sprintf("%v tag scratch:latest %v-one:latest", dockerBinary, repoName)
+	tagCmdFinal := fmt.Sprintf("%v tag emptyfs:latest %v-one:latest", dockerBinary, repoName)
 	tagCmd := exec.Command("bash", "-c", tagCmdFinal)
 	if out, _, err := runCommandWithOutput(tagCmd); err != nil {
 		t.Fatalf("failed to tag repo: %s, %v", out, err)
@@ -378,7 +378,7 @@ func TestSaveMultipleNames(t *testing.T) {
 	defer deleteImages(repoName + "-one")
 
 	// Make two images
-	tagCmdFinal = fmt.Sprintf("%v tag scratch:latest %v-two:latest", dockerBinary, repoName)
+	tagCmdFinal = fmt.Sprintf("%v tag emptyfs:latest %v-two:latest", dockerBinary, repoName)
 	tagCmd = exec.Command("bash", "-c", tagCmdFinal)
 	if out, _, err := runCommandWithOutput(tagCmd); err != nil {
 		t.Fatalf("failed to tag repo: %s, %v", out, err)

project/make/.ensure-scratch

@@ -1,13 +1,13 @@
 #!/bin/bash
 
 if ! docker inspect scratch &> /dev/null; then
-	# let's build a "docker save" tarball for "scratch"
+	# let's build a "docker save" tarball for "emptyfs"
 	# see https://github.com/docker/docker/pull/5262
 	# and also https://github.com/docker/docker/issues/4242
 	mkdir -p /docker-scratch
 	(
 		cd /docker-scratch
-		echo '{"scratch":{"latest":"511136ea3c5a64f264b78b5433614aec563103b4d4702f3ba7d4d2698e22c158"}}' > repositories
+		echo '{"emptyfs":{"latest":"511136ea3c5a64f264b78b5433614aec563103b4d4702f3ba7d4d2698e22c158"}}' > repositories
 		mkdir -p 511136ea3c5a64f264b78b5433614aec563103b4d4702f3ba7d4d2698e22c158
 		(
 			cd 511136ea3c5a64f264b78b5433614aec563103b4d4702f3ba7d4d2698e22c158