kubernetes/kops · error

error marshaling json: %v

Error message

error marshaling json: %v

What it means

After assembling the ExecCredential (cached or freshly issued), the helper serializes it with json.MarshalIndent for output to kubectl. A marshaling failure returns this wrapped error. In practice this is nearly impossible with the fixed ExecCredential struct (only string, time.Time fields), so it almost always indicates corrupt in-memory data such as a cache object with a non-serializable time value.

Source

Thrown at pkg/commands/helpers/kubectl_auth.go:138

		klog.Infof("cached credential had wrong api version")
		cached = nil
	}

	isCached := false
	if cached != nil {
		execCredential = cached
		isCached = true
	} else {
		status, err := buildCredentials(ctx, f, options)
		if err != nil {
			return err
		}
		execCredential.Status = *status
	}

	b, err := json.MarshalIndent(execCredential, "", "  ")
	if err != nil {
		return fmt.Errorf("error marshaling json: %v", err)
	}
	_, err = out.Write(b)
	if err != nil {
		return fmt.Errorf("error writing to stdout: %v", err)
	}

	if !isCached {
		if err := os.MkdirAll(filepath.Dir(cacheFilePath), 0o755); err != nil {
			klog.Warningf("failed to make cache directory for %q: %v", cacheFilePath, err)
		}
		if err := os.WriteFile(cacheFilePath, b, 0o600); err != nil {
			klog.Warningf("failed to write cache file %q: %v", cacheFilePath, err)
		}
	}

	return nil
}

View on GitHub (pinned to 4c8573c808)

Solutions

1. Delete the stale cache file under ~/.kube/cache/kops-authentication/ and re-run so credentials are rebuilt.
2. Check klog output for 'cached credential ... was not valid' and remove the referenced file.
3. If reproducible in a custom build, inspect the ExecCredential content with a debugger.

err := helpers.RunKubectlAuthHelper(ctx, f, out, options)
if err != nil && strings.Contains(err.Error(), "error marshaling json") {
    // clear cache and retry once
    os.RemoveAll(filepath.Join(homedir.HomeDir(), ".kube", "cache", "kops-authentication"))
    err = helpers.RunKubectlAuthHelper(ctx, f, out, options)
}

When it happens

Trigger: json.MarshalIndent(execCredential, ...) returns an error — e.g. a cached ExecCredential unmarshaled into the struct carries an invalid/unsupported field state, or an environment where encoding/json is restricted/patched.

Common situations: Hand-edited cache files in ~/.kube/cache/kops-authentication feeding pathological values; running a heavily modified/custom build; extremely rare Go runtime issues.

Understand the failure class

Background: json.Marshal / "failed to marshal" errors in Go: why "unsupported type" happens and how to fix it — this error's family across 22 libraries.

Related errors

• error building annotation patch: %v
• building node patch: %w
• error building node patch: %v
• marshalling nodeupConfig: %w
• error marshaling json: %v

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/af679ec37a78e9a4. Report an issue: GitHub.