code: func validateServiceExternalTrafficFieldsValue(service *core.Service) field.ErrorList {
  	allErrs := field.ErrorList{}
  
  	// Check first class fields.
  	if service.Spec.ExternalTrafficPolicy != "" &&
  		service.Spec.ExternalTrafficPolicy != core.ServiceExternalTrafficPolicyTypeCluster &&
  		service.Spec.ExternalTrafficPolicy != core.ServiceExternalTrafficPolicyTypeLocal {
  		allErrs = append(allErrs, field.Invalid(field.NewPath("spec").Child("externalTrafficPolicy"), service.Spec.ExternalTrafficPolicy,
  			fmt.Sprintf("ExternalTrafficPolicy must be empty, %v or %v", core.ServiceExternalTrafficPolicyTypeCluster, core.ServiceExternalTrafficPolicyTypeLocal)))
  	}
  	if service.Spec.HealthCheckNodePort < 0 {
  		allErrs = append(allErrs, field.Invalid(field.NewPath("spec").Child("healthCheckNodePort"), service.Spec.HealthCheckNodePort,
  			"HealthCheckNodePort must be not less than 0"))
  	}
  
  	return allErrs
  }
docs: // validateServiceExternalTrafficFieldsValue validates ExternalTraffic related annotations
  // have legal value.