code: public void shutdown() {
          for (Channel c : channels) {
              ChannelPipeline pipeline = c.getPipeline();
              RedisAsyncConnection<?, ?> connection = pipeline.get(RedisAsyncConnection.class);
              connection.close();
          }
          ChannelGroupFuture future = channels.close();
          future.awaitUninterruptibly();
          bootstrap.releaseExternalResources();
      }
docs: Shutdown this client and close all open connections. The client should be
  discarded after calling shutdown.