Whenever a broker stops or crashes leadership for that broker's partitions transfers to other replicas. This means that by default when the broker is restarted it will only be a follower for all its partitions, meaning it will not be used for client reads and writes.

当一个broker停止或崩溃时，这个broker中所有分区的leader将转移给其他副本。这意味着在默认情况下，当这个broker重启之后，它的所有分区都将仅作为follower，不再用于客户端的读写操作。

To avoid this imbalance, Kafka has a notion of preferred replicas. If the list of replicas for a partition is 1,5,9 then node 1 is preferred as the leader to either node 5 or 9 because it is earlier in the replica list. You can have the Kafka cluster try to restore leadership to the restored replicas by running the command:
为了避免这种不平衡，Kafka有一个首选副本的概念。如果一个分区的副本列表是1，5，9，节点1将优先作为其他两个副本5和9的leader，因为它较早存在于副本中。你可以通过运行以下命令让Kafka集群尝试恢复已恢复正常的副本的leader地位：

>
 bin/kafka-preferred-replica-election.sh --zookeeper zk_host:port/chroot

Since running this command can be tedious you can also configure Kafka to do this automatically by setting the following configuration:

手动运行很无趣，你可以通过这个配置设置为自动执行：

    auto.leader.rebalance.enable=true