What causes "failed to unmarshal json: %w" in cilium/cilium?

Run the same command manually with `kubectl exec` and confirm it emits a JSON array

failed to unmarshal json: %w

Error message

failed to unmarshal json: %w

What it means

Shared JSON parser for feature-metrics output: `json.Unmarshal([]byte(output), &encStatus)` into []*models.Metric failed. Any caller (agent or operator fetch) surfaces this wrapped error when the command output is not the expected JSON metric array.

Source

Thrown at cilium-cli/features/status.go:367

}

func ciliumOperatorBinary(pod corev1.Pod) string {
	for _, container := range pod.Spec.Containers {
		if container.Name == defaults.OperatorContainerName {
			for _, cmd := range container.Command {
				if strings.Contains(cmd, "cilium-operator") {
					return cmd
				}
			}
		}
	}
	return ""
}

func nodeStatusFromOutput(output string) ([]*models.Metric, error) {
	var encStatus []*models.Metric
	if err := json.Unmarshal([]byte(output), &encStatus); err != nil {
		return []*models.Metric{}, fmt.Errorf("failed to unmarshal json: %w", err)
	}
	return encStatus, nil
}

type statusPrinter interface {
	printHeader(sorted []string) error
	printNode(metricName, labels string, isBinary bool, values map[float64]struct{}, key string, nodesSorted []string, metricsPerNode map[string]map[string]float64)
	end() error
}

// parseNameAndLabels splits the key into name and labels based on the first ";" separator
func parseNameAndLabels(key string) (string, string) {
	if before, after, found := strings.Cut(key, ";"); found {
		return before, after
	}
	return key, ""
}

View on GitHub (pinned to ac7b90affa)

Solutions

Run the same command manually with `kubectl exec` and confirm it emits a JSON array
Fix the container/binary selection so the real cilium binary runs
Align cilium-cli and Cilium versions so the JSON schema matches models.Metric
Callers should catch this and fall back to skipping metrics collection for that node

Example fix

null

Defensive patterns

Strategy: try-catch

Validate before calling

if strings.TrimSpace(output) == "" {
	return errors.New("empty metrics output; cannot unmarshal")
}

Type guard

func parsesAsMetrics(output string) ([]*models.Metric, bool) {
	var m []*models.Metric
	err := json.Unmarshal([]byte(output), &m)
	return m, err == nil
}

Try / catch

enc, err := nodeStatusFromOutput(out)
if err != nil {
	var uerr *json.UnmarshalTypeError
	if errors.As(err, &uerr) {
		log.Printf("schema mismatch at offset %d: %v", uerr.Offset, uerr)
	}
	return degradeGracefully()
}

Prevention

Verify in-pod command output with kubectl exec before integrating
Keep models.Metric schema aligned with the Cilium version's JSON output
Check for command-usage text (wrong binary) as the root cause
Log raw output on unmarshal failure for debugging

When it happens

Trigger: Output of the in-pod command contains non-JSON content — command-not-found usage text, log lines, truncated output, or empty string — so Unmarshal fails.

Common situations: Wrong container command produced help/usage text; pod output buffer truncated; Cilium version emits a different JSON schema than models.Metric.

Related errors

AI-assisted analysis of cilium/cilium@ac7b90affa (2026-08-31). Data as JSON: /api/errors/84cfc3c2c6703670. Report an issue: GitHub.