docs: function laRoute(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;
      }
      const actives = [];
      if (!client.laParam) {
          client.laParam = {};
      }
      if (client.laParam[serverType]) {
          for (let j = 0; j < servers.length; j++) {
              let count = client.laParam[serverType][servers[j]];
              if (!count) {
                  count = 0;
                  client.laParam[servers[j]] = 0;
              }
              actives.push(count);
          }
      } else {
          client.laParam[serverType] = {};
          for (let i = 0; i < servers.length; i++) {
              client.laParam[serverType][servers[i]] = 0;
              actives.push(0);
          }
      }
      let rs = [];
      let minInvoke = Number.MAX_VALUE;
      for (let k = 0; k < actives.length; k++) {
          if (actives[k] < minInvoke) {
              minInvoke = actives[k];
              rs = [];
              rs.push(servers[k]);
          } else if (actives[k] === minInvoke) {
              rs.push(servers[k]);
          }
      }
      const index = Math.floor(Math.random() * rs.length);
      const serverId = rs[index];
      client.laParam[serverType][serverId] += 1;
      utils.invokeCallback(cb, null, serverId);
  }