kubernetes/kops · error

error building node patch: %v

Error message

error building node patch: %v

What it means

patchNodeLabels marshals a strategic-merge patch (labels map with null for deletions) to JSON before sending it; this wraps json.Marshal failing. The patch structure is built from simple label maps, so a failure here signals an internal bug rather than bad input.

Source

Thrown at cmd/kops-controller/controllers/node_controller.go:161

// patchNodeLabels patches the node labels to set the specified labels
func patchNodeLabels(client *corev1client.CoreV1Client, ctx context.Context, node *corev1.Node, setLabels map[string]string, deleteLabels map[string]struct{}) error {
	nodePatchMetadata := &nodePatchMetadata{
		Labels: make(map[string]*string),
	}
	for k, v := range setLabels {
		v := v
		nodePatchMetadata.Labels[k] = &v
	}
	for k := range deleteLabels {
		nodePatchMetadata.Labels[k] = nil
	}

	nodePatch := &nodePatch{
		Metadata: nodePatchMetadata,
	}
	nodePatchJson, err := json.Marshal(nodePatch)
	if err != nil {
		return fmt.Errorf("error building node patch: %v", err)
	}

	klog.V(2).Infof("sending patch for node %q: %q", node.Name, string(nodePatchJson))

	_, err = client.Nodes().Patch(ctx, node.Name, types.StrategicMergePatchType, nodePatchJson, metav1.PatchOptions{})
	if err != nil {
		return fmt.Errorf("error applying patch to node: %v", err)
	}

	return nil
}

View on GitHub (pinned to 4c8573c808)

Solutions

1. Read the wrapped %v error to see the offending field/type
2. Remove or fix the unmarshalable field in the nodePatch struct
3. Verify all fields have JSON-compatible types and tags

Example fix

// before
Patch Metadata map[string]interface{} `json:"metadata"` // may hold funcs
// after
Patch Metadata *nodePatchMetadata `json:"metadata,omitempty"`

if _, err := json.Marshal(nodePatch); err != nil {
	return fmt.Errorf("error building node patch: %v", err)
}

When it happens

Trigger: json.Marshal(nodePatch) returns an error — practically only if the patch struct contains an unsupported value (e.g. a channel, func, or unmarshalable type added to nodePatch).

Common situations: Extremely rare with the stock struct; would appear if a contributor added a field with a non-serializable type or a bad custom MarshalJSON.

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
• marshaling to json for %v: %w
• error marshaling into JSON: %v
• error parsing version spec %q

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/09c786e5053afb93. Report an issue: GitHub.