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feat: allow specifying Kaniko targets for multi-stage dockerfiles #436

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497d803
Added the ability to specify build targets for kaniko build and an op…
Dec 16, 2024
d09ed90
Fixed linting issues
Jan 6, 2025
9bf8257
Missed a linter error
Jan 7, 2025
a77ad2f
Merge branch 'main' into kaniko-skip-unused
johnstcn Feb 6, 2026
8781126
Merge branch 'main' into kaniko-skip-unused
hamishc Apr 11, 2026
8c7eee7
Added tests for building with a target specified
hamishc Apr 11, 2026
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2 changes: 2 additions & 0 deletions devcontainer/devcontainer.go
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Original file line number Diff line number Diff line change
Expand Up @@ -69,6 +69,7 @@ type Compiled struct {
BuildContext string
FeatureContexts map[string]string
BuildArgs []string
Target string

User string
ContainerEnv map[string]string
Expand Down Expand Up @@ -140,6 +141,7 @@ func (s Spec) HasDockerfile() bool {
func (s *Spec) Compile(fs billy.Filesystem, devcontainerDir, scratchDir string, fallbackDockerfile, workspaceFolder string, useBuildContexts bool, lookupEnv func(string) (string, bool)) (*Compiled, error) {
params := &Compiled{
User: s.ContainerUser,
Target: s.Build.Target,
ContainerEnv: s.ContainerEnv,
RemoteEnv: s.RemoteEnv,
}
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21 changes: 21 additions & 0 deletions devcontainer/devcontainer_test.go
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Expand Up @@ -190,6 +190,27 @@ func TestCompileDevContainer(t *testing.T) {
require.Equal(t, filepath.Join(dcDir, "Dockerfile"), params.DockerfilePath)
require.Equal(t, dcDir, params.BuildContext)
})
t.Run("WithBuildTarget", func(t *testing.T) {
t.Parallel()
fs := memfs.New()
dc := &devcontainer.Spec{
Build: devcontainer.BuildSpec{
Dockerfile: "Dockerfile",
Target: "my-target",
},
}
dcDir := "/workspaces/coder/.devcontainer"
err := fs.MkdirAll(dcDir, 0o755)
require.NoError(t, err)
file, err := fs.OpenFile(filepath.Join(dcDir, "Dockerfile"), os.O_CREATE|os.O_WRONLY, 0o644)
require.NoError(t, err)
_, err = io.WriteString(file, "FROM scratch AS my-target\nUSER testuser")
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@johnstcn johnstcn Apr 11, 2026

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Do we want to also add a second target and then assert that we only go up as far as my-target?

e.g.

FROM scratch AS my-target
USER testuser
FROM my-target AS not-my-target
USER nottestuser

and then assert params.User or similar?

Similarly, what is the expected behaviour for --skip-unused-stages?

require.NoError(t, err)
_ = file.Close()
params, err := dc.Compile(fs, dcDir, workingDir, "", "", false, stubLookupEnv)
require.NoError(t, err)
require.Equal(t, "my-target", params.Target)
})
}

func TestImageFromDockerfile(t *testing.T) {
Expand Down
1 change: 1 addition & 0 deletions docs/env-variables.md
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Expand Up @@ -24,6 +24,7 @@
| `--ignore-paths` | `ENVBUILDER_IGNORE_PATHS` | | The comma separated list of paths to ignore when building the workspace. |
| `--build-secrets` | `ENVBUILDER_BUILD_SECRETS` | | The list of secret environment variables to use when building the image. |
| `--skip-rebuild` | `ENVBUILDER_SKIP_REBUILD` | | Skip building if the MagicFile exists. This is used to skip building when a container is restarting. e.g. docker stop -> docker start This value can always be set to true - even if the container is being started for the first time. |
| `--skip-unused-stages` | `ENVBUILDER_SKIP_UNUSED_STAGES` | | Skip building all unused docker stages. Otherwise it builds by default all stages, even the unnecessary ones until it reaches the target stage / end of Dockerfile. |
| `--git-url` | `ENVBUILDER_GIT_URL` | | The URL of a Git repository containing a Devcontainer or Docker image to clone. This is optional. |
| `--git-clone-depth` | `ENVBUILDER_GIT_CLONE_DEPTH` | | The depth to use when cloning the Git repository. |
| `--git-clone-single-branch` | `ENVBUILDER_GIT_CLONE_SINGLE_BRANCH` | | Clone only a single branch of the Git repository. |
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2 changes: 2 additions & 0 deletions envbuilder.go
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Expand Up @@ -539,6 +539,8 @@ func run(ctx context.Context, opts options.Options, execArgs *execArgsInfo) erro
CustomPlatform: platforms.Format(platforms.Normalize(platforms.DefaultSpec())),
SnapshotMode: "redo",
RunV2: true,
SkipUnusedStages: opts.SkipUnusedStages,
Target: buildParams.Target,
RunStdout: stdoutWriter,
RunStderr: stderrWriter,
Destinations: destinations,
Expand Down
12 changes: 12 additions & 0 deletions options/options.go
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Expand Up @@ -100,6 +100,10 @@ type Options struct {
// This value can always be set to true - even if the container is being
// started for the first time.
SkipRebuild bool
// SkipUnusedStages builds only used stages if defined to true. Otherwise,
// it builds by default all stages, even the unnecessary ones until it
// reaches the target stage / end of Dockerfile
SkipUnusedStages bool
// GitURL is the URL of the Git repository to clone. This is optional.
GitURL string
// GitCloneDepth is the depth to use when cloning the Git repository.
Expand Down Expand Up @@ -359,6 +363,14 @@ func (o *Options) CLI() serpent.OptionSet {
"docker start This value can always be set to true - even if the " +
"container is being started for the first time.",
},
{
Flag: "skip-unused-stages",
Env: WithEnvPrefix("SKIP_UNUSED_STAGES"),
Value: serpent.BoolOf(&o.SkipUnusedStages),
Description: "Skip building all unused docker stages. Otherwise it builds by " +
"default all stages, even the unnecessary ones until it reaches the " +
"target stage / end of Dockerfile.",
},
Comment on lines +366 to +373
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@johnstcn johnstcn Apr 11, 2026

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Where is this actually used?

{
Flag: "git-url",
Env: WithEnvPrefix("GIT_URL"),
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6 changes: 6 additions & 0 deletions options/options_test.go
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Expand Up @@ -37,30 +37,36 @@ func TestEnvOptionParsing(t *testing.T) {
t.Run("bool", func(t *testing.T) {
t.Run("lowercase", func(t *testing.T) {
t.Setenv(options.WithEnvPrefix("SKIP_REBUILD"), "true")
t.Setenv(options.WithEnvPrefix("SKIP_UNUSED_STAGES"), "true")
t.Setenv(options.WithEnvPrefix("GIT_CLONE_SINGLE_BRANCH"), "false")
t.Setenv(options.WithEnvPrefix("GIT_CLONE_THINPACK"), "false")
o := runCLI()
require.True(t, o.SkipRebuild)
require.True(t, o.SkipUnusedStages)
require.False(t, o.GitCloneSingleBranch)
require.False(t, o.GitCloneThinPack)
})

t.Run("uppercase", func(t *testing.T) {
t.Setenv(options.WithEnvPrefix("SKIP_REBUILD"), "TRUE")
t.Setenv(options.WithEnvPrefix("SKIP_UNUSED_STAGES"), "TRUE")
t.Setenv(options.WithEnvPrefix("GIT_CLONE_SINGLE_BRANCH"), "FALSE")
t.Setenv(options.WithEnvPrefix("GIT_CLONE_THINPACK"), "FALSE")
o := runCLI()
require.True(t, o.SkipRebuild)
require.True(t, o.SkipUnusedStages)
require.False(t, o.GitCloneSingleBranch)
require.False(t, o.GitCloneThinPack)
})

t.Run("numeric", func(t *testing.T) {
t.Setenv(options.WithEnvPrefix("SKIP_REBUILD"), "1")
t.Setenv(options.WithEnvPrefix("SKIP_UNUSED_STAGES"), "1")
t.Setenv(options.WithEnvPrefix("GIT_CLONE_SINGLE_BRANCH"), "0")
t.Setenv(options.WithEnvPrefix("GIT_CLONE_THINPACK"), "0")
o := runCLI()
require.True(t, o.SkipRebuild)
require.True(t, o.SkipUnusedStages)
require.False(t, o.GitCloneSingleBranch)
require.False(t, o.GitCloneThinPack)
})
Expand Down
5 changes: 5 additions & 0 deletions options/testdata/options.golden
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Expand Up @@ -179,6 +179,11 @@ OPTIONS:
value can always be set to true - even if the container is being
started for the first time.

--skip-unused-stages bool, $ENVBUILDER_SKIP_UNUSED_STAGES
Skip building all unused docker stages. Otherwise it builds by default
all stages, even the unnecessary ones until it reaches the target
stage / end of Dockerfile.

--ssl-cert-base64 string, $ENVBUILDER_SSL_CERT_BASE64
The content of an SSL cert file. This is useful for self-signed
certificates.
Expand Down
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