docs: function(self, agent, id, cb) {
    let msg = {action: 'subscribe', id: id};
    agent.request(Constants.KEYWORDS.MASTER_WATCHER, msg, function(err, servers) {
      if(err) {
        logger.error('subscribeRequest request to master with error: %j', err.stack);
        utils.invokeCallback(cb, err);
      }
      let res = [];
      for(let id in servers) {
        res.push(servers[id]);
      }
      addServers(self, res);
      utils.invokeCallback(cb);
    });
  }