当broker节点数量发生变化时，需要对已有topics的分区和副本进行重新分配，按照以下步骤来测试一下。
注：--bootstrap-server指定的IP替换为自己的服务器地址
指定主题
首先创建一个json文件，指定要进行重新分配的主题名称
[root@localhost kafka]# vim topics-to-move.json
{
"topics": [
{"topic": "test"}
],
"version": 1
}
先查看一下当前test主题的分配情况，目前分配在0、1、2三个节点上
[root@localhost kafka]# ./bin/kafka-topics.sh --bootstrap-server IP:9092 --topic test --describe
Topic: test TopicId: 8ZUQdSBFSX6bifqtfkqtfw PartitionCount: 3 ReplicationFactor: 3 Configs: segment.bytes=1073741824
Topic: test Partition: 0 Leader: 0 Replicas: 2,1,0 Isr: 2,1,0
Topic: test Partition: 1 Leader: 1 Replicas: 0,2,1 Isr: 1,2,0
Topic: test Partition: 2 Leader: 2 Replicas: 1,0,2 Isr: 0,2,1
生成新的分配计划
使用kafka-reassign-partitions.sh执行以下命令生成一个新的分配计划，其中--broker-list指定要重新分配到哪些broker上（添加或删除后的节点列表）
[root@localhost kafka]# ./bin/kafka-reassign-partitions.sh --bootstrap-server IP:9092 --topics-to-move-json-file topic-to-move.json --broker-list "0,1,2,3" --generate
Current partition replica assignment
{"version":1,"partitions":[{"topic":"test","partition":0,"replicas":[2,1,0],"log_dirs":["any","any","any"]},{"topic":"test","partition":1,"replicas":[1,0,2],"log_dirs":["any","any","any"]},{"topic":"test","partition":2,"replicas":[0,2,1],"log_dirs":["any","any","any"]}]}
Proposed partition reassignment configuration
{"version":1,"partitions":[{"topic":"test","partition":0,"replicas":[0,1,2],"log_dirs":["any","any","any"]},{"topic":"test","partition":1,"replicas":[1,2,3],"log_dirs":["any","any","any"]},{"topic":"test","partition":2,"replicas":[2,3,0],"log_dirs":["any","any","any"]}]}
可以看到Current partition replica assignment是当前分配情况，Proposed partition reassignment configuration是生成的新的分配计划，其中多了一个节点3
创建副本存储计划
把上一步生成的新的分配计划存储到json文件
[root@localhost kafka]# vim increase-replication-factor.json
{"version":1,"partitions":[{"topic":"test","partition":0,"replicas":[0,1,2],"log_dirs":["any","any","any"]},{"topic":"test","partition":1,"replicas":[1,2,3],"log_dirs":["any","any","any"]},{"topic":"test","partition":2,"replicas":[2,3,0],"log_dirs":["any","any","any"]}]}
执行副本存储计划
[root@localhost kafka]# ./bin/kafka-reassign-partitions.sh --bootstrap-server IP:9092 --reassignment-json-file increase-replication-factor.json --execute
Current partition replica assignment
{"version":1,"partitions":[{"topic":"test","partition":0,"replicas":[2,1,0],"log_dirs":["any","any","any"]},{"topic":"test","partition":1,"replicas":[1,0,2],"log_dirs":["any","any","any"]},{"topic":"test","partition":2,"replicas":[0,2,1],"log_dirs":["any","any","any"]}]}
Save this to use as the --reassignment-json-file option during rollback
Successfully started partition reassignments for test-0,test-1,test-2
验证副本存储计划
[root@localhost kafka]# ./bin/kafka-reassign-partitions.sh --bootstrap-server IP:9092 --reassignment-json-file increase-replication-factor.json --verify
Status of partition reassignment:
Reassignment of partition test-0 is complete.
Reassignment of partition test-1 is complete.
Reassignment of partition test-2 is complete.
Clearing broker-level throttles on brokers 0,1,2,3
Clearing topic-level throttles on topic test
重新查看test主题的分配情况，现在0 、1、2、3四个节点都已完成分配
[root@localhost kafka]# ./bin/kafka-topics.sh --bootstrap-server IP:9092 --describe --topic test
Topic: test TopicId: 8ZUQdSBFSX6bifqtfkqtfw PartitionCount: 3 ReplicationFactor: 3 Configs: segment.bytes=1073741824
Topic: test Partition: 0 Leader: 0 Replicas: 0,1,2 Isr: 2,1,0
Topic: test Partition: 1 Leader: 1 Replicas: 1,2,3 Isr: 1,2,3
Topic: test Partition: 2 Leader: 2 Replicas: 2,3,0 Isr: 0,2,3
总结：
- 指定要操作的主题
- 生成副本存储计划
- 执行副本存储计划
- 验证副本存储计划
