code: func (u *Upstream) Identifier() string {
  	name := u.DestinationName
  	if u.DestinationNamespace != "" && u.DestinationNamespace != "default" {
  		name = u.DestinationNamespace + "/" + u.DestinationName
  	}
  	if u.Datacenter != "" {
  		name += "?dc=" + u.Datacenter
  	}
  	typ := u.DestinationType
  	// Service is default type so never prefix it. This is more readable and long
  	// term it is the only type that matters so we can drop the prefix and have
  	// nicer naming in metrics etc.
  	if typ == "" || typ == UpstreamDestTypeService {
  		return name
  	}
  	return typ + ":" + name
  }
docs: // Identifier returns a string representation that uniquely identifies the
  // upstream in a canonical but human readable way.