今天是继续对之前 kafka 集群遗留问题的查漏补缺。
扩容后对副本进行再平衡：
今天检查 kafka manager 发现了一个 __consumer_offsets 主题（消费者分区位移保存主题）的 leader 副本只被部署在了已有三节点中的两个节点上。并没有将三个 broker 上都平均分布上副本，具体表现为
我们点开这个主题
可以发现原本是三个节点的我们，却非常不均匀的只有两个节点承担了存放该 partition 的任务。
所以我们需要重新非配这个 topic 的副本均匀的到三个节点上去。
根据官方文档提供的方法，我们可以借助
./kafka-reassign-partitions.sh --zookeeper 10.171.97.1:2181 --topics-to-move-json-file ~/consumer_offsets_adjust.json --broker-list "0,1,2" --generate
这里的 consumer_offsets_adjust.json 的格式 官方给了一个格式
> cat topics-to-move.json {"topics": [{"topic": "foo1"}, {"topic": "foo2"}], "version":1 }
这里 topics 就是我们想要重新分配的 topics。
命令获得重新分配后的结构。里面的具体参数都很常见在这里不再细说，执行这个命令之后我们会获得一份 再分区前的数据情况，和再分区之后的情况。
我这里贴一份提供格式化之后的 proposed partition reaasigment 我们看下
{ "version": 1, "partitions": [{ "topic": "__consumer_offsets", "partition": 19, "replicas": [2], "log_dirs": ["any"] }, { "topic": "__consumer_offsets", "partition": 10, "replicas": [2], "log_dirs": ["any"] }, { "topic": "__consumer_offsets", "partition": 14, "replicas": [0], "log_dirs": ["any"] }
//中间省略若干 partitions
}
可以看到 replicas 现在有 0 1 2 三个 broker 了。之后我们选择执行该方案，将该方案拷贝进 ~/target.json 文件中再运行：
./kafka-reassign-partitions.sh --zookeeper 10.171.97.1:2181 --reassignment-json-file ~/target.json --execute
就可以开始执行再分配的任务了 另外 kafka 会返回给我们消息
Current partition replica assignment {"version":1,"partitions":[{"topic":"__consumer_offsets","partition":19,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":30,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":47,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":29,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":41,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":39,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":10,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":17,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":14,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":40,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":18,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":26,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":0,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":24,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":33,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":20,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":21,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":3,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":5,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":22,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":12,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":8,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":23,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":15,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":48,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":11,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":13,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":49,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":6,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":28,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":4,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":37,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":31,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":44,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":42,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":34,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":46,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":25,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":45,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":27,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":32,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":43,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":36,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":35,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":7,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":9,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":38,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":1,"replicas":[0],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":16,"replicas":[1],"log_dirs":["any"]},{"topic":"__consumer_offsets","partition":2,"replicas":[1],"log_dirs":["any"]}]} Save this to use as the --reassignment-json-file option during rollback Successfully started reassignment of partitions.
提供给了我们 rollback 的方案，另外这个时候其实就已经开始 ressign 了。ressign 肯定会通知 controller 负责来做这些改变。
我们可以通过命令
./kafka-reassign-partitions.sh --zookeeper 10.171.97.1:2181 --reassignment-json-file ~/target.json --verify
来检查 ressign 进度
Reassignment of partition __consumer_offsets-38 completed successfully Reassignment of partition __consumer_offsets-13 completed successfully Reassignment of partition __consumer_offsets-8 completed successfully Reassignment of partition __consumer_offsets-5 completed successfully Reassignment of partition __consumer_offsets-39 completed successfully Reassignment of partition __consumer_offsets-36 completed successfully Reassignment of partition __consumer_offsets-40 completed successfully Reassignment of partition __consumer_offsets-45 completed successfully
到此位置我们可以来检查一下扩容是否已经成功，leader 副本是否已经被成功的被平均分配到了各个节点上。
首先 kafka brokers spread
leader
可以看到我们完成了！ IT WORKED!这里多提一点是，如果我们需要不让某个 broker 来存储该 topic 的副本的时候，我们同样可以使用 ressign 机制，并且在 broker list 那里去掉对应节点即可。
为已有分区增加 replica：
通过上面的截图大家可能也注意到一个问题，由于历史遗留问题，我们最最最重要的 offsets 提交分区只有一个 replica 也就是只有 leader 副本。通常情况下我们会设置三副本机制使得 broker 挂掉可以轻松切换，所以我们需要为其添加新的 replica vi ~/inc.json 。
{"version":1,
"partitions":[{"topic":"__consumer_offsets","partition":0,"replicas":[0,1,2]}]}
./kafka-reassign-partitions.sh --zookeeper 10.171.97.1:2181 --reassignment-json-file ~/inc.json --execute
我这里只延时了调整一个 partition 的事实上我们需要调整 50个 partitions 。。。。 我就不上脚本了
调整完了之后 Replicas 会变成3副本，但是会带来一个问题就是 ISR 副本肯定需要慢慢才能跟上，还没有跟上的 Under Replicated 数也就是落后副本数肯定满载。变成 true。
但是 ISR 副本数会慢慢跟上来
[2020-01-10 12:03:52,781] INFO [Controller id=0] Updated assigned replicas for partition backend-events-21 being reassigned to 0,1,2 (kafka.controller.KafkaController) [2020-01-10 12:03:52,784] INFO [Controller id=0] Removed partition backend-events-21 from the list of reassigned partitions in zookeeper (kafka.controller.KafkaController) [2020-01-10 12:03:53,124] INFO [Controller id=0] 3/3 replicas have caught up with the leader for partition backend-events-36 being reassigned.Resuming partition reassignment (kafka.controller.KafkaController)
最终会全部赶上来变成下图的情况。
但是呢 现在的 Preferred Leader 还是异常。这里是为什么呢，因为 Replicas 的第一个副本如果是 Leader 说明这里是 Preferred Leader，我们注意上图所有是 false 的地方都违反了这个规则并非是 Replicas 的第一个副本是作为 Leader。所以一会儿会触发 kafka 的 preferred replica 选举.
020-01-10 12:07:09,735] INFO [Controller id=0] Starting preferred replica leader election for partitions backend-events-43 (kafka.controller.KafkaController) [2020-01-10 12:07:09,735] INFO [PartitionStateMachine controllerId=0] Invoking state change to OnlinePartition for partitions backend-events-43 (kafka.controller.PartitionStateMachine) [2020-01-10 12:07:09,740] INFO [PreferredReplicaPartitionLeaderSelector]: Current leader 2 for partition backend-events-43 is not the preferred replica. Triggering preferred replica leader election (kafka.controller.PreferredReplicaPartitionLeaderSelector) [2020-01-10 12:07:09,753] DEBUG [PartitionStateMachine controllerId=0] After leader election, leader cache for backend-events-43 is updated to (Leader:0,ISR:2,0,1,LeaderEpoch:3,ControllerEpoch:42) (kafka.controller.PartitionStateMachine) [2020-01-10 12:07:09,753] INFO [Controller id=0] Partition backend-events-43 completed preferred replica leader election. New leader is 0 (kafka.controller.KafkaController)
最终会变成下面的情况
可以看到这明显有问题，这是因为刚才我在设置 replica 的时候无脑写 0 1 2 ，但是因为顺序关系，第一个副本位置会被设置成 Preferred leader 导致我们 leader 严重偏移了。
现在我们要重新纠正一下这个问题重新执行「增加集群的步骤」重新平衡一下即可，如果你的集群没有开启
auto.leader.rebalance.enable = true
执行完后 可能还需要执行一下
./kafka-preferred-replica-election.sh --zookeeper 10.171.97.1:2181
对 Leader 进行重分配。如果不想这样我们可以在上面增加副本的时候提前设置好 Preferred Leader 来避免重新设置 Leader 平衡的过程。
最后这个时候再来看下我们集群的状态
Not Bad!
-----------------------------------------分割线-----------------------------------------
想再分割线下面再补充一点，磁盘的周期性高 io 可能会引起 kafka 响应时间变慢从而导致 controller 认为该节点已经失效，该节点来不及回复来自 zk 的心跳检查而被踢出集群。
影响了集群的稳定性。
[2020-05-07 23:22:38,125] DEBUG [Controller id=0] Removing replica 3 from ISR 1,0 for partition new-play-atom-online-33. (kafka.controller.KafkaController) [2020-05-07 23:22:38,125] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition new-play-atom-online-33 since it is not in the ISR. Leader = 0 ; ISR = List(1, 0) (kafka.controller.KafkaController) [2020-05-07 23:22:38,125] DEBUG [Controller id=0] Removing replica 3 from ISR 1,2 for partition __consumer_offsets-5. (kafka.controller.KafkaController) [2020-05-07 23:22:38,126] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition __consumer_offsets-5 since it is not in the ISR. Leader = 2 ; ISR = List(1, 2) (kafka.controller.KafkaController) [2020-05-07 23:22:38,126] DEBUG [Controller id=0] Removing replica 3 from ISR 2,1 for partition maxwell_mysql_sync_user-4. (kafka.controller.KafkaController) [2020-05-07 23:22:38,126] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition maxwell_mysql_sync_user-4 since it is not in the ISR. Leader = 1 ; ISR = List(2, 1) (kafka.controller.KafkaController) [2020-05-07 23:22:38,126] DEBUG [Controller id=0] Removing replica 3 from ISR 2,0 for partition __consumer_offsets-6. (kafka.controller.KafkaController) [2020-05-07 23:22:38,126] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition __consumer_offsets-6 since it is not in the ISR. Leader = 2 ; ISR = List(2, 0) (kafka.controller.KafkaController) [2020-05-07 23:22:38,126] DEBUG [Controller id=0] Removing replica 3 from ISR 1,2,3 for partition test_sync_tidb-4. (kafka.controller.KafkaController) [2020-05-07 23:22:38,126] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition test_sync_tidb-4 since it is not in the ISR. Leader = 1 ; ISR = List(1, 2) (kafka.controller.KafkaController) [2020-05-07 23:22:38,126] DEBUG [Controller id=0] Removing replica 3 from ISR 1,0 for partition new-atom-online-32. (kafka.controller.KafkaController) [2020-05-07 23:22:38,127] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition new-atom-online-32 since it is not in the ISR. Leader = 0 ; ISR = List(1, 0) (kafka.controller.KafkaController) [2020-05-07 23:22:38,127] DEBUG [Controller id=0] Removing replica 3 from ISR 2,0 for partition double_write-0. (kafka.controller.KafkaController) [2020-05-07 23:22:38,127] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition double_write-0 since it is not in the ISR. Leader = 2 ; ISR = List(2, 0) (kafka.controller.KafkaController) [2020-05-07 23:22:38,127] DEBUG [Controller id=0] Removing replica 3 from ISR 1,0 for partition sync_tidb-23. (kafka.controller.KafkaController) [2020-05-07 23:22:38,127] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition sync_tidb-23 since it is not in the ISR. Leader = 0 ; ISR = List(1, 0) (kafka.controller.KafkaController) [2020-05-07 23:22:38,127] DEBUG [Controller id=0] Removing replica 3 from ISR 0,2 for partition new-play-atom-online-2. (kafka.controller.KafkaController) [2020-05-07 23:22:38,128] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition new-play-atom-online-2 since it is not in the ISR. Leader = 0 ; ISR = List(0, 2) (kafka.controller.KafkaController) [2020-05-07 23:22:38,128] DEBUG [Controller id=0] Removing replica 3 from ISR 1,2,3 for partition sync_to_aliyun-12. (kafka.controller.KafkaController) [2020-05-07 23:22:38,131] INFO [Controller id=0] New leader and ISR for partition sync_to_aliyun-12 is {"leader":2,"leader_epoch":35,"isr":[1,2]} (kafka.controller.KafkaController) [2020-05-07 23:22:38,131] DEBUG [Controller id=0] Removing replica 3 from ISR 0,1 for partition new-atom-online-39. (kafka.controller.KafkaController) [2020-05-07 23:22:38,131] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition new-atom-online-39 since it is not in the ISR. Leader = 0 ; ISR = List(0, 1) (kafka.controller.KafkaController) [2020-05-07 23:22:38,131] DEBUG [Controller id=0] Removing replica 3 from ISR 1,2 for partition refresh-wjh-15. (kafka.controller.KafkaController) [2020-05-07 23:22:38,131] WARN [Controller id=0] Cannot remove replica 3 from ISR of partition refresh-wjh-15 since it is not in the ISR. Leader = 1 ; ISR = List(1, 2) (kafka.controller.KafkaController) [2020-05-07 23:22:38,147] DEBUG The stop replica request (delete = true) sent to broker 3 is (kafka.controller.ControllerBrokerRequestBatch)
从日志可以看到各 partitions 大规模的移除 replica 3 副本。
Reference:
http://kafka.apache.org/10/documentation.html#basic_ops_cluster_expansion
http://kafka.apache.org/10/documentation.html#basic_ops_increase_replication_factor
https://zhuanlan.zhihu.com/p/38721205 KAFKA集群扩容后的数据迁移