What causes "invalid context directory - %s" in slimtoolkit/slim?

Fix the `build.context` path in the compose file so it points to an existing directory relative to the compose file's directory

slimtoolkit/slim · error

invalid context directory - %s

Error message

invalid context directory - %s

What it means

buildImage resolves the build context directory for a service's build config; if the resolved contextDir (joined with the base compose dir when relative) does not exist or is not a directory per os.Stat, it returns 'invalid context directory - %s'. The image build cannot proceed without a valid context directory.

Source

Thrown at pkg/app/master/compose/execution.go:1194

	}

	//TODO: investigate []string to string
	if len(config.ExtraHosts) > 0 {
		buildOptions.ExtraHosts = config.ExtraHosts[0]
	}

	if strings.HasPrefix(config.Context, "http://") || strings.HasPrefix(config.Context, "https://") {
		buildOptions.Remote = config.Context
	} else {
		contextDir := config.Context
		if !strings.HasPrefix(contextDir, "/") {
			contextDir = filepath.Join(basePath, contextDir)
		}

		if info, err := os.Stat(contextDir); err == nil && info.IsDir() {
			buildOptions.ContextDir = contextDir
		} else {
			return fmt.Errorf("invalid context directory - %s", contextDir)
		}
	}

	if err := apiClient.BuildImage(buildOptions); err != nil {
		log.Debugf("buildImage: dockerapi.BuildImage() error = %v", err)
		return err
	}

	fmt.Println("build output:")
	fmt.Println(output.String())
	fmt.Println("build output [DONE]")

	return nil
}

func durationToSeconds(d *types.Duration) int {
	if d == nil {
		return 0

View on GitHub (pinned to 81940d17fa)

Solutions

Fix the `build.context` path in the compose file so it points to an existing directory relative to the compose file's directory
Verify the directory exists with ls/os.stat at the resolved location (base compose dir + context)
If running from a different cwd or inside a container, ensure the base compose directory and the build context are accessible/mounted

Example fix

// before (docker-compose.yml)
  app:
    build:
      context: ./sr          # typo, directory missing
// after
  app:
    build:
      context: ./src

Defensive patterns

Strategy: validation

Validate before calling

func checkBuildContext(baseDir string, svc types.ServiceConfig) error {
    if svc.Build == nil {
        return nil
    }
    ctx := svc.Build.Context
    if !filepath.IsAbs(ctx) {
        ctx = filepath.Join(baseDir, ctx)
    }
    info, err := os.Stat(ctx)
    if err != nil || !info.IsDir() {
        return fmt.Errorf("build context %q does not exist or is not a dir", ctx)
    }
    return nil
}

Try / catch

if err := compose.BuildImage(ctx, cli, baseDir, imgName, buildCfg); err != nil {
    if strings.HasPrefix(err.Error(), "invalid context directory") {
        return fmt.Errorf("fix build.context path: %w", err)
    }
    return err
}

Prevention

Use paths relative to the compose file location and verify they exist
Run `docker compose config` to see resolved build contexts
When running in containers, mount the build context directory
Commit Dockerfile directories to the repo so they always exist

When it happens

Trigger: Building a service whose `build.context` points to a nonexistent path, a file instead of a directory, or a path that is wrong once joined with the base compose dir (relative paths resolved against the wrong base).

Common situations: Typos in build.context; running the tool from a different working directory than expected; a Dockerfile directory deleted or renamed; using an absolute path valid on another machine; missing volume mount in containerized runs.

Related errors

AI-assisted analysis of slimtoolkit/slim@81940d17fa (2026-08-31). Data as JSON: /api/errors/8dac4b9d51e93d76. Report an issue: GitHub.