docs: public synchronized boolean shutdown() {
          if (channel == null) {
              return false;
          }
          Address address = channel.getAddress();
          LOGGER.debug("{0} shutting down clustering service...", address);
          consumers.clear();
  
          // Mark this as not accepting any more ...
          isOpen.set(false);
          
          try {
              // Disconnect from the channel and close it ...
              channel.disconnect();
              channel.removeChannelListener(listener);
              channel.setReceiver(null);
              channel.close();
              LOGGER.debug("{0} successfully closed main channel", address);
          } finally {
              channel = null;
          }
          membersInCluster.set(1);
          return true;
      }