docs: @Override
      public String serviceToUrl(String protocol, String serviceId, String tag, String requestKey) {
          URL url = loadBalance.select(discovery(protocol, serviceId, tag), requestKey);
          if(logger.isDebugEnabled()) logger.debug("final url after load balance = " + url);
          // construct a url in string
          return protocol + "://" + url.getHost() + ":" + url.getPort();
      }