grafana/k6 · error

failed to encode load zone list: %w

Error message

failed to encode load zone list: %w

What it means

`k6 cloud load-zones list --json` (cmdCloudLoadZoneList.outputJSON) encodes the fetched load-zone slice with encoding/json and wraps an encoder failure in this message. For plain data structs like LoadZone, Encode cannot fail in practice — there are no channels, funcs, or cyclic references — so hitting this error indicates an internal defect or memory-level fault rather than a user mistake.

Source

Thrown at internal/cmd/cloud_load_zone_list.go:77

	stackHeader := fmt.Sprintf("Load zones for %s:\n\n", cloudStackName(cloudConfig))

	if len(loadZones) == 0 {
		printToStdout(c.globalState, stackHeader+"No load zones found.\n")
		return nil
	}

	printToStdout(c.globalState, stackHeader+formatLoadZoneTable(loadZones))
	return nil
}

func (c *cmdCloudLoadZoneList) outputJSON(loadZones []cloudapiv6.LoadZone) error {
	buf := &bytes.Buffer{}
	enc := json.NewEncoder(buf)
	enc.SetEscapeHTML(false)
	enc.SetIndent("", "  ")
	if err := enc.Encode(loadZones); err != nil {
		return fmt.Errorf("failed to encode load zone list: %w", err)
	}

	printToStdout(c.globalState, buf.String())
	return nil
}

func formatLoadZoneTable(loadZones []cloudapiv6.LoadZone) string {
	var buf strings.Builder
	w := tabwriter.NewWriter(&buf, 0, 0, 3, ' ', 0)
	_, _ = fmt.Fprintln(w, "ID\tNAME\tTYPE\tAVAILABLE")
	for _, z := range loadZones {
		zoneType := "private"
		if z.Public {
			zoneType = "public"
		}
		available := "no"
		if z.Available {
			available = "yes"

View on GitHub (pinned to 93accf6570)

Solutions

1. Run the command without --json (table output) to confirm the API call itself works
2. Upgrade or downgrade k6 to a version where this path is known-good
3. Report the bug to grafana/k6 with the k6 version and full output

Example fix

# before
k6 cloud load-zones list --json
# after
k6 cloud load-zones list  # table output as a workaround

if err := cmdCloudLoadZoneList.outputJSON(zones); err != nil {
    // fall back to table output; encoder failure is internal, data itself is valid
    printToStdout(gs, formatLoadZoneTable(zones))
}

When it happens

Trigger: Running the load-zone list command with --json output while json.Encoder.Encode returns an error; realistically only reachable if a LoadZone field type stops being serializable in a future k6 version.

Common situations: Essentially never seen; would appear right after a k6 upgrade that changed the LoadZone model, on any invocation regardless of environment.

Related errors

• failed to encode test list: %w
• failed to encode project list: %w
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AI-assisted analysis of grafana/k6@93accf6570 (2026-08-15). Data as JSON: /api/errors/9d7dc47d3bc8635f. Report an issue: GitHub.