feat: Add buildx option for daemon-less BuildKit support

`docker buildx build` can be configured to execute a remote buildkit instance.
No docker daemon is necessary for this to work.

This commit removes dependencies on docker daemon if `buildx` is used, so `skaffold build` can be used in a CI without docker daemon.

pkg/skaffold/build/docker/docker.go

@@ -72,7 +72,7 @@ func (b *Builder) Build(ctx context.Context, out io.Writer, a *latest.Artifact,
 	// ignore useCLI boolean if buildkit is enabled since buildkit is only implemented for docker CLI at the moment in skaffold.
 	// we might consider a different approach in the future.
 	// use CLI for cross-platform builds
-	if b.useCLI || (b.useBuildKit != nil && *b.useBuildKit) || len(a.DockerArtifact.CliFlags) > 0 || matcher.IsNotEmpty() {
+	if b.useCLI || b.buildx || (b.useBuildKit != nil && *b.useBuildKit) || len(a.DockerArtifact.CliFlags) > 0 || matcher.IsNotEmpty() {
 		imageID, err = b.dockerCLIBuild(ctx, output.GetUnderlyingWriter(out), a.ImageName, a.Workspace, dockerfile, a.ArtifactType.DockerArtifact, opts, pl)
 	} else {
 		imageID, err = b.localDocker.Build(ctx, out, a.Workspace, a.ImageName, a.ArtifactType.DockerArtifact, opts)
@@ -93,6 +93,9 @@ func (b *Builder) Build(ctx context.Context, out io.Writer, a *latest.Artifact,
 
 func (b *Builder) dockerCLIBuild(ctx context.Context, out io.Writer, name string, workspace string, dockerfilePath string, a *latest.DockerArtifact, opts docker.BuildOptions, pl v1.Platform) (string, error) {
 	args := []string{"build", workspace, "--file", dockerfilePath, "-t", opts.Tag}
+	if b.buildx {
+		args = append([]string{"buildx"}, args...)
+	}
 	imgRef, err := docker.ParseReference(opts.Tag)
 	if err != nil {
 		return "", fmt.Errorf("couldn't parse image tag: %w", err)
@@ -110,6 +113,9 @@ func (b *Builder) dockerCLIBuild(ctx context.Context, out io.Writer, name string
 	if err != nil {
 		return "", fmt.Errorf("getting docker build args: %w", err)
 	}
+	if b.buildx && b.pushImages {
+		cliArgs = append(cliArgs, "--push")
+	}
 	args = append(args, cliArgs...)
 
 	if b.cfg.Prune() {
@@ -142,7 +148,11 @@ func (b *Builder) dockerCLIBuild(ctx context.Context, out io.Writer, name string
 		return "", tryExecFormatErr(fmt.Errorf("running build: %w", err), errBuffer)
 	}
 
-	return b.localDocker.ImageID(ctx, opts.Tag)
+	if b.buildx {
+		return "", nil // TODO: return id from CLI
+	} else {
+		return b.localDocker.ImageID(ctx, opts.Tag)
+	}
 }
 
 func (b *Builder) pullCacheFromImages(ctx context.Context, out io.Writer, a *latest.DockerArtifact, pl v1.Platform) error {

pkg/skaffold/build/docker/docker_test.go

@@ -161,7 +161,7 @@ func TestDockerCLIBuild(t *testing.T) {
 			}
 			t.Override(&util.OSEnviron, func() []string { return []string{"KEY=VALUE"} })
 
-			builder := NewArtifactBuilder(fakeLocalDaemonWithExtraEnv(test.extraEnv), test.cfg, test.localBuild.UseDockerCLI, test.localBuild.UseBuildkit, false, mockArtifactResolver{make(map[string]string)}, nil)
+			builder := NewArtifactBuilder(fakeLocalDaemonWithExtraEnv(test.extraEnv), test.cfg, test.localBuild.UseDockerCLI, false, test.localBuild.UseBuildkit, false, mockArtifactResolver{make(map[string]string)}, nil)
 
 			artifact := &latest.Artifact{
 				Workspace: ".",
@@ -242,7 +242,7 @@ func TestDockerCLICheckCacheFromArgs(t *testing.T) {
 			)
 			t.Override(&util.DefaultExecCommand, mockCmd)
 
-			builder := NewArtifactBuilder(fakeLocalDaemonWithExtraEnv([]string{}), mockConfig{}, true, util.Ptr(false), false, mockArtifactResolver{make(map[string]string)}, nil)
+			builder := NewArtifactBuilder(fakeLocalDaemonWithExtraEnv([]string{}), mockConfig{}, true, false, util.Ptr(false), false, mockArtifactResolver{make(map[string]string)}, nil)
 			_, err := builder.Build(context.Background(), io.Discard, &a, test.tag, platform.Matcher{})
 			t.CheckNoError(err)
 		})

pkg/skaffold/build/docker/errors_test.go

@@ -60,7 +60,7 @@ Refer https://skaffold.dev/docs/references/yaml/#build-artifacts-docker for deta
 				"docker build . --file "+dockerfilePath+" -t tag",
 			))
 			t.Override(&docker.DefaultAuthHelper, stubAuth{})
-			builder := NewArtifactBuilder(fakeLocalDaemonWithExtraEnv([]string{}), mockConfig{}, true, nil, false, mockArtifactResolver{make(map[string]string)}, nil)
+			builder := NewArtifactBuilder(fakeLocalDaemonWithExtraEnv([]string{}), mockConfig{}, true, false, nil, false, mockArtifactResolver{make(map[string]string)}, nil)
 
 			artifact := &latest.Artifact{
 				ImageName: "test-image",

pkg/skaffold/build/docker/types.go

@@ -29,6 +29,7 @@ type Builder struct {
 	cfg                docker.Config
 	pushImages         bool
 	useCLI             bool
+	buildx             bool
 	useBuildKit        *bool
 	artifacts          ArtifactResolver
 	sourceDependencies TransitiveSourceDependenciesResolver
@@ -45,12 +46,13 @@ type TransitiveSourceDependenciesResolver interface {
 }
 
 // NewBuilder returns an new instance of a docker builder
-func NewArtifactBuilder(localDocker docker.LocalDaemon, cfg docker.Config, useCLI bool, useBuildKit *bool, pushImages bool, ar ArtifactResolver, dr TransitiveSourceDependenciesResolver) *Builder {
+func NewArtifactBuilder(localDocker docker.LocalDaemon, cfg docker.Config, useCLI bool, buildx bool, useBuildKit *bool, pushImages bool, ar ArtifactResolver, dr TransitiveSourceDependenciesResolver) *Builder {
 	return &Builder{
 		localDocker:        localDocker,
 		pushImages:         pushImages,
 		cfg:                cfg,
 		useCLI:             useCLI,
+		buildx:             buildx,
 		useBuildKit:        useBuildKit,
 		artifacts:          ar,
 		sourceDependencies: dr,

pkg/skaffold/build/local/local.go

@@ -90,11 +90,16 @@ func (b *Builder) buildArtifact(ctx context.Context, out io.Writer, a *latest.Ar
 
 	imageID := digestOrImageID
 	b.builtImages = append(b.builtImages, imageID)
-	return build.TagWithImageID(ctx, tag, imageID, b.localDocker)
+
+	if b.local.Buildx {
+		return "", nil
+	} else {
+		return build.TagWithImageID(ctx, tag, imageID, b.localDocker)
+	}
 }
 
 func (b *Builder) runBuildForArtifact(ctx context.Context, out io.Writer, a *latest.Artifact, tag string, platforms platform.Matcher) (string, error) {
-	if !b.pushImages {
+	if !b.local.Buildx && !b.pushImages {
 		// All of the builders will rely on a local Docker:
 		// + Either to build the image,
 		// + Or to docker load it.

pkg/skaffold/build/local/types.go

@@ -148,7 +148,7 @@ type artifactBuilder interface {
 func newPerArtifactBuilder(b *Builder, a *latest.Artifact) (artifactBuilder, error) {
 	switch {
 	case a.DockerArtifact != nil:
-		return dockerbuilder.NewArtifactBuilder(b.localDocker, b.cfg, b.local.UseDockerCLI, b.local.UseBuildkit, b.pushImages, b.artifactStore, b.sourceDependencies), nil
+		return dockerbuilder.NewArtifactBuilder(b.localDocker, b.cfg, b.local.UseDockerCLI, b.local.Buildx, b.local.UseBuildkit, b.pushImages, b.artifactStore, b.sourceDependencies), nil
 
 	case a.BazelArtifact != nil:
 		return bazel.NewArtifactBuilder(b.localDocker, b.cfg, b.pushImages), nil

pkg/skaffold/schema/latest/config.go

@@ -311,6 +311,8 @@ type LocalBuild struct {
 	// UseDockerCLI use `docker` command-line interface instead of Docker Engine APIs.
 	UseDockerCLI bool `yaml:"useDockerCLI,omitempty"`
 
+	Buildx bool `yaml:"buildx,omitempty"`
+
 	// UseBuildkit use BuildKit to build Docker images. If unspecified, uses the Docker default.
 	UseBuildkit *bool `yaml:"useBuildkit,omitempty"`