kubernetes/kops · error

failed to marsal %q into json: %w

Error message

failed to marsal %q into json: %w

What it means

createManagedFieldPatch marshals the constructed patchObject (containing apiVersion, kind, and metadata with the merged managed fields) using json.MarshalIndent for readability. A failure here is wrapped with a typo'd message "failed to marsal %q into json" naming the current object. This aborts creation of the migration patch.

Source

Thrown at pkg/applylib/applyset/managedfields.go:111

		if fixedManagedFields[i].Subresource != fixedManagedFields[j].Subresource {
			return fixedManagedFields[i].Subresource < fixedManagedFields[j].Subresource
		}
		if fixedManagedFields[i].Operation != fixedManagedFields[j].Operation {
			return fixedManagedFields[i].Operation < fixedManagedFields[j].Operation
		}
		return false
	})

	meta := &metav1.ObjectMeta{}
	meta.SetManagedFields(fixedManagedFields)
	patchObject := map[string]interface{}{
		"metadata": meta,
	}

	// MarshalIndent is a little less efficient, but makes this much more readable (also helps tests)
	jsonData, err := json.MarshalIndent(patchObject, "", "  ")
	if err != nil {
		return nil, fmt.Errorf("failed to marsal %q into json: %w", currentObject.GetName(), err)
	}
	return jsonData, nil
}

// fieldManagerKey is the primary key for a ManagedFieldEntry
type fieldManagerKey struct {
	Manager     string
	Operation   metav1.ManagedFieldsOperationType
	Subresource string
}

// mergeFieldManagers merges the managed fields from identical field managers.
// If we don't do this, the apiserver will not currently construct the union for duplicate keys.
func mergeFieldManagers(managedFields []metav1.ManagedFieldsEntry) ([]metav1.ManagedFieldsEntry, error) {
	byKey := make(map[fieldManagerKey][]metav1.ManagedFieldsEntry)
	for _, f := range managedFields {
		k := fieldManagerKey{
			Manager:     f.Manager,

View on GitHub (pinned to 4c8573c808)

Solutions

1. Check the wrapped error for the unencodable type and which object (%q) triggered it.
2. Upgrade/align k8s.io/apimachinery and sigs.k8s.io/structured-merge-diff versions so FieldsV1 round-trips cleanly.
3. As a workaround, re-create the object with server-side apply from scratch (kubectl apply --server-side --force-conflicts) instead of migrating in place.

if _, err := json.MarshalIndent(patchObject, "", "  "); err != nil {
    return fmt.Errorf("patch for %s not marshalable: %w", name, err)
}

if _, err := migrator.Migrate(ctx, obj); err != nil && strings.Contains(err.Error(), "failed to marsal") {
    // fall back to recreating the object via server-side apply
    return recreateWithSSA(ctx, obj)
}

When it happens

Trigger: json.MarshalIndent fails on the patchObject map — typically because a value placed in the patch structure (e.g. an entry from the object's managedFields or a FieldsV1-parsed set) contains a type Go's encoding/json cannot encode, such as NaN floats or non-marshalable internal types.

Common situations: An API server or library version returning managedFields data that, after conversion to fieldpath.Set and back, yields unencodable values; a bug in constructing the patchObject; rarely seen in practice since inputs come from the API server's own types.

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

• failed to create managed-fields patch: %w
• failed to patch object managed-fields for %q: %w
• no managed fields supplied
• cannot merge ManagedFieldsEntry apiVersion %q with apiVersio
• failed to marshal object to JSON: %w

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/7b7c5f072e1f81cc. Report an issue: GitHub.