code: public boolean request(String nodeId, String message) {
          if (!channelAvailable(nodeId)) {
              try {
                  lazyInit(nodeId);
              } catch (ApplicationInstanceOfflineException nodeOffline) {
                  LOG.warn("Warning, node is offline.", nodeOffline);
                  return false;
              } catch (Exception e) {
                  LOG.error("Error, unexpected exception.", e);
                  return false;
              }
          }
          if (LOG.isDebugEnabled())
              LOG.debug(String.format(">>>> rpc to %s  >>> remoteAddress=%s", nodeId, nodeId_to_connectedChannel_map.get(nodeId).remoteAddress()));
          nodeId_to_connectedChannel_map.get(nodeId).writeAndFlush(message + Constant.RPC_DELIMITER);
          return true;
      }
docs: 异步发送器，如果要同步，请在你自己那一层阻塞，如果消息发送失败则返回false