docs: function chRoute(client, serverType, msg, cb) {
      const servers = client._station.serversMap[serverType];
      if (!servers || !servers.length) {
          utils.invokeCallback(cb, new Error(`rpc servers not exist with serverType: ${serverType}`));
          return;
      }
      let con;
      if (!client.chParam) {
          client.chParam = {};
      }
      if (client.chParam[serverType]) {
          con = client.chParam[serverType].consistentHash;
      } else {
          client.opts.station = client._station;
          con = new ConsistentHash(servers, client.opts);
      }
      const hashFieldIndex = client.opts.hashFieldIndex;
      const field = msg.args[hashFieldIndex] || JSON.stringify(msg);
      utils.invokeCallback(cb, null, con.getNode(field));
      client.chParam[serverType] = { consistentHash: con };
  }