kubernetes/kops · error

unable to marshal JSON: %v

Error message

unable to marshal JSON: %v

What it means

In RunGetKeypairs' OutputJSON branch, json.Marshal(items) serializes the []*keypairItem slice. If marshaling fails, the command returns "unable to marshal JSON: %v". json.Marshal only errors on unsupported types (channels, funcs, cyclic structures), so this indicates a data/shape problem rather than user input.

Source

Thrown at cmd/kops/get_keypairs.go:249

		columnNames := []string{"NAME", "ID", "ISSUED", "EXPIRES"}
		if options.Distrusted {
			columnNames = append(columnNames, "DISTRUSTED")
		}
		columnNames = append(columnNames, "PRIMARY", "HASPRIVATE")
		return t.Render(items, out, columnNames...)

	case OutputYaml:
		y, err := yaml.Marshal(items)
		if err != nil {
			return fmt.Errorf("unable to marshal YAML: %v", err)
		}
		if _, err := out.Write(y); err != nil {
			return fmt.Errorf("error writing to output: %v", err)
		}
	case OutputJSON:
		j, err := json.Marshal(items)
		if err != nil {
			return fmt.Errorf("unable to marshal JSON: %v", err)
		}
		if _, err := out.Write(j); err != nil {
			return fmt.Errorf("error writing to output: %v", err)
		}

	default:
		return fmt.Errorf("unknown output format: %q", options.Output)
	}

	return nil
}

func completeGetKeypairs(ctx context.Context, f commandutils.Factory, options *GetKeypairsOptions, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
	commandutils.ConfigureKlogForCompletion()

	cluster, clientSet, completions, directive := GetClusterForCompletion(ctx, f, nil)
	if cluster == nil {
		return completions, directive

View on GitHub (pinned to 4c8573c808)

Solutions

1. Read the wrapped %v cause — json.Marshal errors name the exact type it cannot encode.
2. Try `-o yaml` or `-o table` to still inspect the keypairs.
3. Check whether local modifications to cmd/kops/get_keypairs.go introduced an unsupported field; revert or add a marshaler.
4. If caused by store data, verify state-store contents and kOps version compatibility.

Example fix

// before
type keypairItem struct {
	Cert *x509.Certificate // fields fine, but a chan/func field would break Marshal
}
// after
Ensure all exported fields are JSON-encodable, or add:
func (i *keypairItem) MarshalJSON() ([]byte, error) { ... }

if err := runKops("get", "keypairs", "-o", "json"); err != nil {
	if strings.Contains(err.Error(), "unable to marshal JSON") {
		// data-shape problem: fall back to table output and report wrapped cause
	}
	return err
}

When it happens

Trigger: `kops get keypairs -o json` where keypairItem contains a value json.Marshal cannot encode — e.g. a field of an unsupported type or an unexpected data shape loaded from the key store.

Common situations: Custom patches to keypairItem introducing unencodable fields; corrupted or unusual keyset metadata from the state store; version mismatch between the CLI and state-store data format.

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 marshaling json: %v
• error writing json to stdout: %v
• unable to marshal JSON: %v
• unable to marshal JSON: %v
• error marshaling json: %v

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/49f8d7714406aa1a. Report an issue: GitHub.