code: func GetServiceNetworkTier(service *v1.Service) (cloud.NetworkTier, error) {
  	l, ok := service.Annotations[NetworkTierAnnotationKey]
  	if !ok {
  		return cloud.NetworkTierDefault, nil
  	}
  
  	v := cloud.NetworkTier(l)
  	switch v {
  	case cloud.NetworkTierStandard:
  		fallthrough
  	case cloud.NetworkTierPremium:
  		return v, nil
  	default:
  		return cloud.NetworkTierDefault, fmt.Errorf("unsupported network tier: %q", v)
  	}
  }
docs: // GetServiceNetworkTier returns the network tier of GCP load balancer
  // which should be assembled, and an error if the specified tier is not
  // supported.