假如Kafka集群中一个broker宕机无法恢复，应该如何处理？

假如Kafka集群中一个broker宕机无法恢复, 应该如何处理?

今天面试时遇到这个问题, 网上资料说添加新的broker, 是不会自动同步旧数据的.

笨办法

环境介绍

三个broker的集群, zk,kafka装在一起

| broker | IP | broker.id |
|---------|---------------|-----------|
| broker1 | 172.18.12.211 | 211 |
| broker2 | 172.18.12.212 | 212 |
| broker3 | 172.18.12.213 | 213 |

创建测试topic

#./bin/kafka-topics.sh --zookeeper 172.18.12.212:2181 --create --topic test1 --replication-factor 3 --partitions 1
Created topic "test1".

查看

#./bin/kafka-topics.sh --zookeeper 172.18.12.212:2181 --describe --topic test1
Topic:test1 PartitionCount:1 ReplicationFactor:3 Configs:
        Topic: test1 Partition: 0 Leader: 213 Replicas: 213,212,211 Isr: 213,212,211

注意当前
Replicas: 213,212,211
Isr: 213,212,211

造一些消息

#./bin/kafka-console-producer.sh --broker-list 172.18.12.212:9092 --topic test1
>1
>2
>3

kill broker2

[root@node024212 ~]# ps -ef| grep kafka
root 17633 1 1 Feb17 ? 00:55:18 /usr/local/java/bin/java -server -Xmx2g - ...
[root@node024212 ~]# kill -9 17633
[root@node024212 ~]# ps -ef| grep kafka
root 21875 21651 0 11:27 pts/2 00:00:00 grep --color=auto kafka

稍等一会, 再次describe test1

#./bin/kafka-topics.sh --zookeeper 172.18.12.212:2181 --describe --topic test1
Topic:test1 PartitionCount:1 ReplicationFactor:3 Configs:
        Topic: test1 Partition: 0 Leader: 213 Replicas: 213,212,211 Isr: 213,211

可看到副本仍然是Replicas: 213,212,211
ISR已经变为Isr: 213,211

在212启动新broker

创建一份新的配置文件, 自动一个新的broker

# cp server.properties server2.properties 
# vim server2.properties 
只修改这两个参数
broker.id=218
log.dirs=/DATA21/kafka/kafka-logs,/DATA22/kafka/kafka-logs,/DATA23/kafka/kafka-logs,/DATA24/kafka/kafka-logs

创建相应目录

mkdir -p /DATA21/kafka/kafka-logs
mkdir -p /DATA22/kafka/kafka-logs
mkdir -p /DATA23/kafka/kafka-logs
mkdir -p /DATA24/kafka/kafka-logs

启动新broker

./bin/kafka-server-start.sh -daemon config/server2.properties 

稍等, 查看 test1 状态

#./bin/kafka-topics.sh --zookeeper 172.18.12.212:2181 --describe --topic test1
Topic:test1 PartitionCount:1 ReplicationFactor:3 Configs:
        Topic: test2 Partition: 0 Leader: 213 Replicas: 213,212,211 Isr: 213,218,211

可以看到 test1 副本仍然是Replicas: 213,212,211
ISR为Isr: 213,218,211. 也就是说缺失的副本不会自动迁移到新broker上.

使用kafka-reassign-partitions.sh重分配分区

将212删除,添加218

[root@node024211 12:04:48 /usr/local/kafka]
#echo '{"version":1,"partitions":[{"topic":"test1","partition":0,"replicas":[211,213,218]}]}' > increase-replication-factor.json

[root@node024211 12:58:30 /usr/local/kafka]
#./bin/kafka-reassign-partitions.sh --zookeeper 172.18.12.211:2181 --reassignment-json-file increase-replication-factor.json --execute
Current partition replica assignment

{"version":1,"partitions":[{"topic":"test1","partition":0,"replicas":[213,212,211],"log_dirs":["any","any","any"]}]}

Save this to use as the --reassignment-json-file option during rollback
Successfully started reassignment of partitions.

[root@node024211 12:58:49 /usr/local/kafka]
#./bin/kafka-reassign-partitions.sh --zookeeper 172.18.12.211:2181 --reassignment-json-file increase-replication-factor.json --verify
Status of partition reassignment: 
Reassignment of partition test1-0 completed successfully

查看topic信息

#./bin/kafka-topics.sh --zookeeper 172.18.12.212:2181 --describe --topic test1
Topic:test1 PartitionCount:1 ReplicationFactor:3 Configs:
        Topic: test1 Partition: 0 Leader: 213 Replicas: 211,213,218 Isr: 213,211,218

验证218是否有全部数据

虽然看副本信息中已经有了218, 但是218是否包含旧消息呢?
我的办法是, kill 211,213, 然后–from-beginning 消费218数据, 实际测试也是可以的

#./bin/kafka-console-consumer.sh --bootstrap-server 172.18.12.212:9092 --topic test1 --from-beginning
1
2
3
4
5
6
7
8
9
10
11
11

看了下211 218的log文件大小也是一样的

[2019-02-21 13:29:19]#ls -l /DATA22/kafka/kafka-logs/test1-0/
[2019-02-21 13:29:19]total 8
[2019-02-21 13:29:19]-rw-r--r--. 1 root root 10485760 Feb 21 12:58 00000000000000000000.index
[2019-02-21 13:29:19]-rw-r--r--. 1 root root 381 Feb 21 13:00 00000000000000000000.log
[2019-02-21 13:29:19]-rw-r--r--. 1 root root 10485756 Feb 21 12:58 00000000000000000000.timeindex
[2019-02-21 13:29:19]-rw-r--r--. 1 root root 16 Feb 21 13:00 leader-epoch-checkpoint

更简单的办法

通过阅读文档发现
https://cwiki.apache.org/confluence/display/KAFKA/FAQ#FAQ-Howtoreplaceafailedbroker

How to replace a failed broker?
When a broker fails, Kafka doesn’t automatically re-replicate the data on the failed broker to other brokers. This is because in the common case, one brings down a broker to apply code or config changes, and will bring up the broker quickly afterward. Re-replicating the data in this case will be wasteful. In the rarer case that a broker fails completely, one will need to bring up another broker with the same broker id on a new server. The new broker will automatically replicate the missing data.

这上面说的,如果服务器真的坏了, 只需要新启动一个broker, 把broker.id设置为 损坏的那个broker的id, 就会自动复制过去丢失的数据。

实际测试了一下, 确实可以恢复。