在前面的文章《Kafka集群扩展以及重新分布分区》中，我们将介绍如何通过Kafka自带的工具来增加Topic的分区数量。本文将简单地介绍如何通过Kafka自带的工具来动态增加Tpoic的副本数。首先来看看我们操作的Topic相关的信息

[iteblog@www.iteblog.com ~]$ kafka-topics.sh --topic iteblog --describe --zookeeper www.iteblog.com:2181
Topic:iteblog  PartitionCount:2  ReplicationFactor:1 Configs:
  Topic: iteblog Partition: 0  Leader: 2 Replicas: 2 Isr: 2
  Topic: iteblog Partition: 1  Leader: 3 Replicas: 3 Isr: 3

从上面的输出信息可以看出，iteblog主题有两个分区，副本数为1。假如我们需要将这个主题的副本数增加到3，以便提供高可用性。
　　动态地增加相关主题的副本数非常的简单，同样是使用kafka-reassign-partitions.sh工具来执行，所以我们在操作之前得准备一个Json文件，里面详细地记录着每个分区的副本所在机器等信息，具体如下：

{
    "version": 1, 
    "partitions": [
        {
            "topic": "iteblog", 
            "partition": 0, 
            "replicas": [
                2, 
                1, 
                3
            ]
        },
        {
            "topic": "iteblog", 
            "partition": 1, 
            "replicas": [
                3, 
                2, 
                1
            ]
        }
    ]
}

上面已经把主题的副本数变成3了，我们把这个Json数据存放在名为replication.json的文件中。现在我们需要执行这个配置文件，如下：

[iteblog@www.iteblog.com ~]$ kafka-reassign-partitions.sh --zookeeper www.iteblog.com:2181 --reassignment-json-file replication.json --execute
Current partition replica assignment

{"version":1,"partitions":[{"topic":"iteblog","partition":0,"replicas":[2]},{"topic":"iteblog","partition":1,"replicas":[3]}]}

Save this to use as the --reassignment-json-file option during rollback
Successfully started reassignment of partitions {"version":1,"partitions":[{"topic":"iteblog","partition":0,"replicas":[2,1,3]},{"topic":"iteblog","partition":1,"replicas":[3,2,1]}]}

同样我们可以使用verify参数来检查上面的执行计划是否完成，如下：

[iteblog@www.iteblog.com ~]$ kafka-reassign-partitions.sh --zookeeper www.iteblog.com:2181 --reassignment-json-file replication.json --verify
Status of partition reassignment:
Reassignment of partition [iteblog,0] is still in progress
Reassignment of partition [iteblog,1] is still in progress

[iteblog@www.iteblog.com ~]$ kafka-reassign-partitions.sh --zookeeper www.iteblog.com:2181 --reassignment-json-file replication.json --verify
Status of partition reassignment:
Reassignment of partition [iteblog,0] completed successfully
Reassignment of partition [iteblog,1] completed successfully

好了，我们可以看出上面的执行计划已经完成。我们来查看一下现在iteblog主题的相关信息：

[iteblog@www.iteblog.com ~]$ kafka-topics.sh --topic iteblog --describe --zookeeper www.iteblog.com:2181
Topic:iteblog  PartitionCount:2  ReplicationFactor:3 Configs:
  Topic: iteblog Partition: 0  Leader: 2 Replicas: 2,1,3 Isr: 2,1,3
  Topic: iteblog Partition: 1  Leader: 3 Replicas: 3,2,1 Isr: 3,2,1

可以看出，iteblog主题的副本数已经变成了3，好了收工。