code: func ExtractHostID(hostName string, clusterName string) (string, error) {
  	suffix := "." + clusterName
  	if !strings.HasSuffix(hostName, suffix) {
  		return "", trace.BadParameter("expected suffix %q in %q", suffix, hostName)
  	}
  	return strings.TrimSuffix(hostName, suffix), nil
  }
docs: // ExtractHostID returns host id based on the hostname