kubernetes/kops · error

failed to serialize kops-controller config: %v

Error message

failed to serialize kops-controller config: %v

What it means

After building the kops-controller config struct, KopsControllerConfig serializes it with json.Marshal (JSON is a subset of YAML). If marshaling fails, this error wraps it. In practice json.Marshal of a plain struct essentially never fails, so this indicates a marshaling edge case or corruption of the config struct (e.g. unsupported types reached via embedded options).

Source

Thrown at upup/pkg/fi/cloudup/template_functions.go:938

			config.Server.Provider.Linode = &linode.LinodeVerifierOptions{}

		case kops.CloudProviderMetal:
			// Use crypto public/private keys for Metal
			config.Server.PKI = &pkibootstrap.Options{}

		default:
			return "", fmt.Errorf("unsupported cloud provider %s", cluster.GetCloudProvider())
		}
	}

	if cluster.Spec.IsKopsControllerIPAM() {
		config.EnableCloudIPAM = true
	}

	// To avoid indentation problems, we marshal as json.  json is a subset of yaml
	b, err := json.Marshal(config)
	if err != nil {
		return "", fmt.Errorf("failed to serialize kops-controller config: %v", err)
	}

	return string(b), nil
}

// KopsControllerArgv returns the args to kops-controller
func (tf *TemplateFunctions) KopsControllerArgv() ([]string, error) {
	var argv []string

	// Verbose, but not excessive logging
	argv = append(argv, "--v=2")

	argv = append(argv, "--conf=/etc/kubernetes/kops-controller/config/config.yaml")

	return argv, nil
}

func (tf *TemplateFunctions) ExternalDNSArgv() ([]string, error) {

View on GitHub (pinned to 4c8573c808)

Solutions

1. Inspect the wrapped error to identify the unmarshalable field/type.
2. If you added a new field to the config struct, change its type to something JSON-marshalable (or add json:"-").
3. Report upstream if hit on an unmodified kOps build.

Example fix

// before
Debug chan struct{} `json:"debug"`
// after
Debug bool `json:"debug"`

// Go
b, err := json.Marshal(config)
if err != nil {
    // log full config struct type to locate the offending field
    klog.Errorf("kops-controller config marshal failed: %v", err)
    return "", fmt.Errorf("failed to serialize kops-controller config: %v", err)
}

When it happens

Trigger: json.Marshal(config) returns an error inside KopsControllerConfig — effectively only if the config struct contains a value that cannot be marshaled (unsupported type, channel, func field, or a custom MarshalJSON returning an error).

Common situations: Extremely rare in normal use; mostly encountered when hacking on kOps itself, adding a new field of an unmarshalable type to pkibootstrap.Options or the kops-controller config struct.

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
• error building node patch: %v
• marshalling nodeupConfig: %w
• error marshaling json: %v

AI-assisted analysis of kubernetes/kops@4c8573c808 (2026-09-05). Data as JSON: /api/errors/6d258f05b54af32d. Report an issue: GitHub.