buildkit: introduce initial support

This patch adds a new entry `Buildkit` to the RFC2822 image manifest
files, allowing individual image components to opt into buildkit
support, using docker buildx.

Additionally, docker build is changed to explicitly set
DOCKER_BUILDKIT=0 to force a non-buildkit build in preparation for
switching the default in any upcoming docker versions.

Signed-off-by: Justin Chadwell <me@jedevc.com>

cmd/bashbrew/cmd-build.go

@@ -2,6 +2,7 @@ package main
 
 import (
  "fmt"
+ "strings"
 
  "github.com/urfave/cli"
 )
@@ -77,6 +78,18 @@ func cmdBuild(c *cli.Context) error {
  return cli.NewMultiError(fmt.Errorf(`failed calculating "cache hash" for %q (tags %q)`, r.RepoName, entry.TagsString()), err)
  }
 
+ var buildkit bool
+ switch strings.ToLower(entry.Buildkit) {
+ case "false":
+ buildkit = false
+ case "true":
+ buildkit = true
+ case "":
+ buildkit = false
+ default:
+ return cli.NewMultiError(fmt.Errorf(`invalid value for buildkit %s, expected "true" or "false"`, entry.Buildkit))
+ }
+
  // check whether we've already built this artifact
  _, err = dockerInspect("{{.Id}}", cacheTag)
  if err != nil {
@@ -95,16 +108,20 @@ func cmdBuild(c *cli.Context) error {
 
  // TODO use "meta.StageNames" to do "docker build --target" so we can tag intermediate stages too for cache (streaming "git archive" directly to "docker build" makes that a little hard to accomplish without re-streaming)
 
- var extraEnv []string = nil
- if fromScratch {
- // https://github.com/docker/cli/blob/v20.10.7/cli/command/image/build.go#L163
- extraEnv = []string{"DOCKER_DEFAULT_PLATFORM=" + ociArch.String()}
- // ideally, we would set this via an explicit "--platform" flag on "docker build", but it's not supported without buildkit until 20.10+ and this is a trivial way to get Docker to do the right thing in both cases without explicitly trying to detect whether we're on 20.10+
- }
-
- err = dockerBuild(cacheTag, entry.ArchFile(arch), archive, extraEnv)
- if err != nil {
- return cli.NewMultiError(fmt.Errorf(`failed building %q (tags %q)`, r.RepoName, entry.TagsString()), err)
+ if buildkit {
+ err = dockerBuildx(cacheTag, entry.ArchFile(arch), archive, ociArch.String())
+ if err != nil {
+ return cli.NewMultiError(fmt.Errorf(`failed building %q (tags %q)`, r.RepoName, entry.TagsString()), err)
+ }
+ } else {
+ var platform string
+ if fromScratch {
+ platform = ociArch.String()
+ }
+ err = dockerBuild(cacheTag, entry.ArchFile(arch), archive, platform)
+ if err != nil {
+ return cli.NewMultiError(fmt.Errorf(`failed building %q (tags %q)`, r.RepoName, entry.TagsString()), err)
+ }
  }
  archive.Close() // be sure this happens sooner rather than later (defer might take a while, and we want to reap zombies more aggressively)
  }

cmd/bashbrew/docker.go

@@ -13,8 +13,8 @@ import (
  "strconv"
  "strings"
 
- "github.com/urfave/cli"
  "github.com/docker-library/bashbrew/manifest"
+ "github.com/urfave/cli"
 )
 
 type dockerfileMetadata struct {
@@ -237,16 +237,57 @@ func (r Repo) dockerBuildUniqueBits(entry *manifest.Manifest2822Entry) ([]string
  return uniqueBits, nil
 }
 
-func dockerBuild(tag string, file string, context io.Reader, extraEnv []string) error {
+func dockerBuild(tag string, file string, context io.Reader, platform string) error {
  args := []string{"build", "--tag", tag, "--file", file, "--rm", "--force-rm"}
  args = append(args, "-")
  cmd := exec.Command("docker", args...)
- if extraEnv != nil {
- cmd.Env = append(os.Environ(), extraEnv...)
+ cmd.Env = append(os.Environ(), "DOCKER_BUILDKIT=0")
+ if debugFlag {
+ fmt.Println("$ export DOCKER_BUILDKIT=0")
+ }
+ if platform != "" {
+ // ideally, we would set this via an explicit "--platform" flag on "docker build", but it's not supported without buildkit until 20.10+ and this is a trivial way to get Docker to do the right thing in both cases without explicitly trying to detect whether we're on 20.10+
+ // https://github.com/docker/cli/blob/v20.10.7/cli/command/image/build.go#L163
+ cmd.Env = append(cmd.Env, "DOCKER_DEFAULT_PLATFORM="+platform)
  if debugFlag {
- fmt.Printf("$ export %q\n", extraEnv)
+ fmt.Printf("$ export DOCKER_DEFAULT_PLATFORM=%q\n", platform)
+ }
+ }
+ cmd.Stdin = context
+ if debugFlag {
+ cmd.Stdout = os.Stdout
+ cmd.Stderr = os.Stderr
+ fmt.Printf("$ docker %q\n", args)
+ return cmd.Run()
+ } else {
+ buf := &bytes.Buffer{}
+ cmd.Stdout = buf
+ cmd.Stderr = buf
+ err := cmd.Run()
+ if err != nil {
+ err = cli.NewMultiError(err, fmt.Errorf(`docker %q output:%s`, args, "\n"+buf.String()))
  }
+ return err
+ }
+}
+
+const dockerfileSyntax = "docker/dockerfile:1"
+
+func dockerBuildx(tag string, file string, context io.Reader, platform string) error {
+ args := []string{
+ "buildx",
+ "build",
+ "--progress", "plain",
+ "--build-arg", "BUILDKIT_SYNTAX=" + dockerfileSyntax,
+ "--tag", tag,
+ "--file", file,
+ }
+ if platform != "" {
+ args = append(args, "--platform", platform)
  }
+ args = append(args, "-")
+
+ cmd := exec.Command("docker", args...)
  cmd.Stdin = context
  if debugFlag {
  cmd.Stdout = os.Stdout

manifest/rfc2822.go

@@ -44,6 +44,8 @@ type Manifest2822Entry struct {
  Directory string
  File string
 
+ Buildkit string
+
  // architecture-specific versions of the above fields
  ArchValues map[string]string
  // "ARCH-FIELD: VALUE"