docs: public RemotingCommand invokeSync(RemotingCommand request)
              throws JobTrackerNotFoundException {
  
          Node jobTracker = getJobTrackerNode();
  
          try {
              RemotingCommand response = remotingClient.invokeSync(jobTracker.getAddress(),
                      request, appContext.getConfig().getInvokeTimeoutMillis());
              this.serverEnable = true;
              return response;
          } catch (Exception e) {
              // 将这个JobTracker移除
              jobTrackers.remove(jobTracker);
              try {
                  Thread.sleep(100L);
              } catch (InterruptedException e1) {
                  LOGGER.error(e1.getMessage(), e1);
              }
              // 只要不是节点 不可用, 轮询所有节点请求
              return invokeSync(request);
          }
      }