Allow configuring app directory/path binaries are placed into by UnseenWizzard · Pull Request #1403 · ko-build/ko

UnseenWizzard · 2024-09-20T13:43:50Z

This PR proposes a way to allow optionally modifying under which path binaries are placed inside containers built with ko - as raised in issue #944

Without deeper insight into the code base, this seems like a straightforward addition with limited impact on future maintainability to me - while allowing users migrating to ko to still place binaries in the same location as their previous Docker containers.

Looking forward to your input and any suggestions!

UnseenWizzard · 2024-09-20T13:45:01Z

pkg/build/gobuild_test.go

+	entryPointBasePath string
+}
+
+func validateImage(t *testing.T, img oci.SignedImage, baseLayers int64, creationTime v1.Time, opts validationOptions) {


note that baseLayers being 3 in all test uses triggers the linter - as it's unrelated to the change, I didn't want to change the function to appease the linter. lmk if I should

Thanks, just use your PR locally. Appreciate for the project, but not sure why we need branded entrypoints (Makefile, workflows already has references)...

github-actions · 2024-12-20T01:28:03Z

This Pull Request is stale because it has been open for 90 days with
no activity. It will automatically close after 30 more days of
inactivity. Keep fresh with the 'lifecycle/frozen' label.

maboehm · 2025-04-11T11:51:02Z

@UnseenWizzard @imjasonh
Really a bummer to see this PR get stale and closed. We would really find this feature helpful and that change (while adding some new functionality to maintain) is non-intrusive and non-breaking.

Could we re-open this PR?

UnseenWizzard · 2025-04-11T12:27:11Z

From my perspective I'm very happy to reopen this PR and make any changes needed to get in! Just let me know

I just honestly got the impression from the issue discussions, that a feature like this, while relevant to a part of the user base, is not of interest to maintainers. Which is a pity.

cpanato · 2025-04-11T13:02:24Z

reopened, i also agree with that would be a nice feature

Laubi · 2025-04-15T09:10:21Z

This feature would also be really nice for us, as we don't want to introduce breaking changes into existing images. What is needed to merge this feature?

The currently hardcoded 'ko-app' app directory was used as a hardcoded string in several places in gobuild. To simplify making it overwritable, all occurances are extraced into a constant for the default value.

An option is added to overwrite the default /ko-app folder to place app binaries in. This can be set via cmd line flag or as a default in the config file.

UnseenWizzard · 2025-04-18T18:53:00Z

@cpanato change is rebased and conflicts (in docs/ only) resolved :)
CI ran successfully on my fork - note the comment about linting above, lmk if and how you want that addressed with this PR.

I'd also like to add an E2E test for this change - should that simply be added as another part of the Build and run [...] step in the e2e.yaml action? Or would it make sense to split that action into more than one step?

(Btw I can't view why the license compliance check fails here but it seems to do the same on main?)

rfranzke · 2025-05-07T07:37:58Z

We would also very much like to have this feature :) Can we do something to move this PR forward?

hakman · 2025-06-28T08:54:11Z

This would be very useful to lots of projects.
@justinsb had a similar PR, but I think he missed the feedback from @imjasonh. #1128 (review)
@cpanato @imjasonh could you take another look? Thanks!

imjasonh · 2026-03-23T19:49:17Z

It sounds like there's sufficient interest in this feature that we should move forward on it. I've resolved a merge conflict and will review now.

Copilot

Pull request overview

This PR adds a configurable “app directory” so ko can place built binaries somewhere other than the default /ko-app inside the resulting image, addressing issue #944 for users who need stable absolute binary paths.

Changes:

Add --app-dir flag and .ko.yaml config key defaultAppDirectory, and plumb them into the build options.
Thread the configured app directory through the Go builder so entrypoint/PATH (and debugger paths) use the configured directory.
Add/adjust tests and update reference/configuration docs to document the new flag and config.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
pkg/commands/resolver.go	Passes `BuildOptions.AppDirectory` into the build layer via `build.WithAppDir`.
pkg/commands/options/build.go	Introduces `AppDirectory`, wires `--app-dir`, and loads `defaultAppDirectory` from config.
pkg/build/options.go	Adds `build.WithAppDir` functional option.
pkg/build/gobuild.go	Applies configurable app dir to entrypoint/PATH and layer creation logic.
pkg/build/gobuild_test.go	Updates validation harness and adds tests for custom app dir + debugger interaction.
docs/reference/ko_{run,resolve,create,build,apply}.md	Documents the new `--app-dir` flag in CLI reference output.
docs/configuration.md	Documents `.ko.yaml` config key `defaultAppDirectory` and behavior overview.

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Copilot · 2026-03-23T19:53:29Z

pkg/build/gobuild.go

+		appPath := strings.Replace(path.Join("C:", g.getAppDir(), appFileName), "/", `\`, -1)
 		if g.debug {
 			cfg.Config.Entrypoint = append([]string{"C:\\" + delvePath}, delveArgs...)
 			cfg.Config.Entrypoint = append(cfg.Config.Entrypoint, appPath)
 		} else {
 			cfg.Config.Entrypoint = []string{appPath}
 		}

-		updatePath(cfg, `C:\ko-app`)
+		addDirPath := strings.Replace(path.Join("C:", g.getAppDir()), "/", `\`, -1)
+		updatePath(cfg, addDirPath)


Windows path construction is likely broken when appDir starts with "/" (default and most user values). In Go, path.Join("C:", "/ko-app", ...) discards the "C:" prefix, producing a path like "\ko-app\..." after replacement. This will yield an invalid entrypoint and PATH entry on Windows. Consider handling Windows separately (e.g., trim a leading slash from appDir before joining, or build the path using a Windows-aware join) so the result is always rooted at "C:\".

Copilot · 2026-03-23T19:53:30Z

pkg/build/gobuild.go

 	// Write the parent directories to the tarball archive.
 	// For Windows, the layer must contain a Hives/ directory, and the root
 	// of the actual filesystem goes in a Files/ directory.
 	// For Linux, the binary goes into /ko-app/
-	dirs := []string{"ko-app"}
+	dirs := []string{binaryDir}
 	if platform.OS == "windows" {
 		dirs = []string{
 			"Hives",
 			"Files",
-			"Files/ko-app",
+			path.Join("Files", binaryDir),
 		}
 		name = "Files" + name


tarBinary now writes directory headers using binaryDir directly. If binaryDir is an absolute path like "/ko-app" or "/usr/local/bin", the Windows branch's path.Join("Files", binaryDir) will ignore the "Files" prefix (because the second argument is absolute), and the layer will not contain the expected "Files/..." directory structure. It also only writes a single directory header (not all parent segments) despite the comment saying it writes parent directories. Consider normalizing binaryDir to a relative path for tar entry names (e.g., trim leading "/" and split into segments to write each parent), and for Windows always prefix with "Files/" after normalization.

Copilot · 2026-03-23T19:53:30Z

pkg/build/options.go

+func WithAppDir(dir string) Option {
+	return func(gbo *gobuildOpener) error {
+		gbo.appDir = dir
+		return nil
+	}
+}


WithAppDir accepts any string and passes it through unmodified. Because this value influences tar entry names, the image entrypoint, and PATH, it’s worth normalizing and validating it (e.g., path.Clean, reject empty/"."/".." segments, and require an absolute POSIX path for non-Windows). This avoids surprising runtime failures when users pass relative paths or paths with trailing slashes.

Copilot · 2026-03-23T19:53:30Z

pkg/commands/options/build.go

 	WorkingDirectory string

+	// AppDirectory allows for setting where the Go application binaries will be placed in the resulting container.
+	// Empty string means the default directly /ko-app.


The comment says "Empty string means the default directly /ko-app." which reads like a grammar mistake and is a bit unclear. Suggest rewording to something like "Empty string means the default directory: /ko-app." to avoid ambiguity.

Suggested change

// Empty string means the default directly /ko-app.

// Empty string means the default directory: /ko-app.

Copilot · 2026-03-23T19:53:30Z

pkg/commands/options/build.go

+	if bo.AppDirectory == "" {
+		if appDir := v.GetString("defaultAppDirectory"); appDir != "" {
+			bo.AppDirectory = appDir
+		}
+	}


LoadConfig now supports a new config key (defaultAppDirectory), but there’s no accompanying unit test verifying: (1) the key is read from .ko.yaml, and (2) the CLI flag (--app-dir) properly overrides the config value. Adding a small test in pkg/commands/options/build_test.go (and a testdata .ko.yaml) would prevent regressions.

Copilot · 2026-03-23T19:53:31Z

pkg/build/gobuild_test.go

+		want := "/ko-app/test"
+		if opts.entryPointBasePath != "" {
+			want = path.Join(opts.entryPointBasePath, "test")
+		}
+		if got := entrypoint[0]; got != want {
 			t.Errorf("entrypoint = %v, want %v", got, want)
 		}
 	})


The new app-dir feature is only asserted via config (entrypoint/PATH), but the tests don’t verify that the binary actually exists in the layer at that directory. Since validateImage doesn’t currently inspect the binary layer tar headers, a regression in tarBinary/buildLayer path handling could slip through. Consider extending these assertions to read the binary layer tar and confirm the expected entry (e.g., /test) is present when entryPointBasePath is set.

Copilot · 2026-03-23T19:53:31Z

pkg/build/gobuild_test.go

+		t.Fatalf("Build() not an Image: %T", result)
+	}
+
+	// Check that the entrypoint of the image is not overwritten


This comment seems incorrect: the test is asserting that the entrypoint is overwritten to include dlv and then the app path. Consider rewording to avoid confusion (e.g., "Check that the entrypoint includes the debugger and uses the configured app dir").

Suggested change

// Check that the entrypoint of the image is not overwritten

// Check that the entrypoint includes the debugger and uses the configured app dir

UnseenWizzard commented Sep 20, 2024

View reviewed changes

github-actions bot added the lifecycle/stale label Dec 20, 2024

github-actions bot closed this Jan 19, 2025

cpanato reopened this Apr 11, 2025

cpanato added lifecycle/frozen and removed lifecycle/stale labels Apr 11, 2025

UnseenWizzard force-pushed the feat/allow-overwriting-app-directory branch from 6fa8faf to 2342b17 Compare April 15, 2025 06:25

UnseenWizzard added 3 commits April 18, 2025 20:35

refactor: Extract hardcoded default app dir into a constant

bf307eb

The currently hardcoded 'ko-app' app directory was used as a hardcoded string in several places in gobuild. To simplify making it overwritable, all occurances are extraced into a constant for the default value.

feat: Allow optionally defining in which directory binaries are placed

a1a788d

An option is added to overwrite the default /ko-app folder to place app binaries in. This can be set via cmd line flag or as a default in the config file.

docs: Describe overwriting directory executables are placed into

0795ff9

UnseenWizzard force-pushed the feat/allow-overwriting-app-directory branch from 2342b17 to 0795ff9 Compare April 18, 2025 18:35

timebertt mentioned this pull request May 7, 2025

gardener-node-agent: support images built by ko gardener/gardener#12021

Merged

Merge branch 'main' into feat/allow-overwriting-app-directory

8598244

Copilot AI review requested due to automatic review settings March 23, 2026 19:48

Copilot started reviewing on behalf of imjasonh March 23, 2026 19:49 View session

Copilot AI reviewed Mar 23, 2026

View reviewed changes

	// Empty string means the default directly /ko-app.
	// Empty string means the default directory: /ko-app.

	// Check that the entrypoint of the image is not overwritten
	// Check that the entrypoint includes the debugger and uses the configured app dir

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den-vasyliev Feb 21, 2026 •

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UnseenWizzard commented Apr 11, 2025 •

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