'Flags metadata for update, return Future()
Actual update must be handled separately. This method will only
change the reported ttl()
Returns:
kafka.future.Future (value will be the cluster object after update)'

def request_update(self):

    with self._lock:
        self._need_update = True
        if ((not self._future) or self._future.is_done):
            self._future = Future()
        return self._future
