docs: function failover(code, tracer, serverId, msg, opts, cb) {
      let servers;
      const self = this;
      const serverType = msg.serverType;
      if (!tracer.servers) {
          servers = self.serversMap[serverType];
      } else {
          servers = tracer.servers;
      }
  
      const index = servers.indexOf(serverId);
      if (index >= 0) {
          servers.splice(index, 1);
      }
      tracer.servers = servers;
  
      if (!servers.length) {
          logger.error('[dreamix-rpc] rpc failed with all this type of servers, with serverType: %s', serverType);
          utils.invokeCallback(cb, new Error(`rpc failed with all this type of servers, with serverType: ${serverType}`));
          return;
      }
      self.dispatch.call(self, tracer, servers[0], msg, opts, cb);
  }