GoogleContainerTools/skaffold · error

marshalling yaml: %w

Error message

marshalling yaml: %w

What it means

applyDebuggingTransforms decodes each Kubernetes manifest from YAML, applies debugging transforms to inject the debugging support containers, and re-encodes the object back to YAML. This error is returned when the mutated object cannot be marshalled back into YAML by encodeAsYaml. It indicates the transformed in-memory Kubernetes object (signature, port, env, annotation fields injected by the debugger retriever) failed json/yaml serialization.

Source

Thrown at pkg/skaffold/kubernetes/debugging/transform.go:102

	kind = gvk.Kind
	if group == "" {
		description = fmt.Sprintf("%s/%s", strings.ToLower(kind), name)
	} else {
		description = fmt.Sprintf("%s.%s/%s", strings.ToLower(kind), group, name)
	}
	return
}

func applyDebuggingTransforms(l manifest.ManifestList, retriever debug.ConfigurationRetriever, debugHelpersRegistry string) (manifest.ManifestList, error) {
	var updated manifest.ManifestList
	for _, manifest := range l {
		obj, _, err := decodeFromYaml(manifest, nil, nil)
		if err != nil {
			log.Entry(context.Background()).Debugf("Unable to interpret manifest for debugging: %v\n", err)
		} else if transformManifest(obj, retriever, debugHelpersRegistry) {
			manifest, err = encodeAsYaml(obj)
			if err != nil {
				return nil, fmt.Errorf("marshalling yaml: %w", err)
			}
			if log.IsDebugLevelEnabled() {
				log.Entry(context.Background()).Debugln("Applied debugging transform:\n", string(manifest))
			}
		}
		updated = append(updated, manifest)
	}

	return updated, nil
}

// isPortAvailable returns true if none of the pod's containers specify the given port.
func isPortAvailable(podSpec *v1.PodSpec, port int32) bool {
	for _, container := range podSpec.Containers {
		for _, portSpec := range container.Ports {
			if portSpec.ContainerPort == port {
				return false
			}

View on GitHub (pinned to a1189de023)

Solutions

1. Check the wrapped error in the message to identify which field failed to marshal
2. Verify the manifest decodes cleanly: run the skaffold debug pipeline on a minimal, standard k8s YAML to isolate the offending resource
3. Update the runtime/serialization dependencies (sigs.k8s.io/yaml, k8s.io/apimachinery) to match the k8s library version Skaffold expects
4. If only a specific artifact fails, temporarily disable debugging for that artifact (--profile without debug) to confirm the transform is the cause

Example fix

// before: transform injects a value the encoder chokes on; log and skip the transform
manifest, err = encodeAsYaml(obj)
if err != nil {
    return nil, fmt.Errorf("marshalling yaml: %w", err)
}
// after: fall back to the untransformed manifest
manifest, err = encodeAsYaml(obj)
if err != nil {
    log.Entry(context.Background()).Warnf("skipping debugging transform, encode failed: %v", err)
    // keep original manifest
}

// pre-validate the manifest decodes
var raw map[string]interface{}
if err := yaml.Unmarshal([]byte(manifest), &raw); err != nil {
    return fmt.Errorf("manifest is not valid YAML, debugging transform would fail later: %w", err)
}

func isMarshallable(obj runtime.Object) bool {
    _, err := json.Marshal(obj)
    return err == nil
}

updated, err := debug.ApplyDebuggingTransforms(ctx, manifests, retriever)
if err != nil {
    if strings.Contains(err.Error(), "marshalling yaml") {
        log.Warnf("debug transform failed on a manifest, continuing untransformed: %v", err)
        return originalManifests, nil
    }
    return nil, err
}

When it happens

Trigger: An artifact with debugging support enabled is deployed; decodeFromYaml succeeds but transformManifest returns true (transforms were applied) and encodeAsYaml then fails on the mutated object — e.g. the transform injected a value that the k8s runtime serializer cannot marshal.

Common situations: Debugging a container runtarget with an unusual base image where the retrieved debugger config produces non-serializable values; Kubernetes manifest files containing unusual types; a broken/unsupported resource kind that partially decodes and then fails on encode after transformation.

Related errors

• marshalling yaml: %w
• invalid local-registry-hosting ConfigMap
• marshalling configuration: %w
• marshaling new config: %w
• marshaling config: %w

AI-assisted analysis of GoogleContainerTools/skaffold@a1189de023 (2026-09-05). Data as JSON: /api/errors/ad27012d1fa07de1. Report an issue: GitHub.