kubernetes/kops · error

error writing json to stdout: %v

Error message

error writing json to stdout: %v

What it means

Wraps any error from fullOutputJSON, which serializes the fetched objects to JSON and writes them to stdout. This mirrors error 342 for the JSON path; the underlying failure is either a marshaling/codec error or a write error on the output stream.

Source

Thrown at cmd/kops/get_all.go:136

		for _, group := range instancegroups {
			allObjects = append(allObjects, group)
		}
		for _, additionalObject := range addonObjects {
			allObjects = append(allObjects, additionalObject)
		}
	}

	switch options.Output {
	case OutputYaml:
		if err := fullOutputYAML(out, allObjects...); err != nil {
			return fmt.Errorf("error writing yaml to stdout: %v", err)
		}

		return nil

	case OutputJSON:
		if err := fullOutputJSON(out, false, allObjects...); err != nil {
			return fmt.Errorf("error writing json to stdout: %v", err)
		}
		return nil

	case OutputTable:
		fmt.Fprintf(out, "Cluster\n")
		err = clusterOutputTable([]*api.Cluster{cluster}, out)
		if err != nil {
			return err
		}
		fmt.Fprintf(out, "\nInstance Groups\n")
		err = igOutputTable(cluster, instancegroups, out)
		if err != nil {
			return err
		}
		if len(addonObjects) != 0 {
			fmt.Fprintf(out, "\nAddon Objects\n")
			err = addonsOutputTable(cluster, addonObjects, out)
			if err != nil {

View on GitHub (pinned to 4c8573c808)

Solutions

1. Inspect the wrapped inner error for the marshal vs write distinction
2. Align kops CLI version with the cluster state-store version
3. Use `--name`/full cluster name and rerun; verify state store readability
4. Write to a file instead of a pipe to avoid write failures

Example fix

// before
j, err := fullOutputJSON(out, false, allObjects...)
if err != nil { return fmt.Errorf("error writing json to stdout: %v", err) }
// after
if err := fullOutputJSON(buf, false, allObjects...); err != nil { return err }
_, err = out.Write(buf.Bytes())

if err := fullOutputJSON(out, false, allObjects...); err != nil {
    if errors.Is(err, syscall.EPIPE) {
        return nil // downstream consumer closed stdout
    }
    return fmt.Errorf("error writing json to stdout: %v", err)
}

When it happens

Trigger: `kops get all <cluster> -o json` where object serialization via the codecs fails (unregistered kind, version conversion) or the write to stdout fails.

Common situations: State-store objects from a newer kops version with fields the current codecs reject; piping to a closed pipe; scripting `kops get all -o json` and consuming output while the writer errors.

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

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/df2de8ccba97f5a9. Report an issue: GitHub.