def add_broker(self, broker):
        """Add broker to current broker-list."""
        if broker not in self._brokers:
            self._brokers.add(broker)
        else:
            self.log.warning(
                'Broker {broker_id} already present in '
                'replication-group {rg_id}'.format(
                    broker_id=broker.id,
                    rg_id=self._id,
                )
            )
Add broker to current broker-list.