参考文章：https://blog.csdn.net/russle/article/details/83421904
一、问题描述
实际项目中我们可能在创建topic时没有设置好正确的replication-factor，（默认情况为1份），导致kafka集群虽然是高可用的，但是该topic所在的broker宕机时，可能发生无法使用的情况。topic一旦使用又不能轻易删除重建，因此动态增加副本因子就成为最终的选择。
二、问题解决
首先本地编辑一个json文件reassign.json如下：
/*
*# The replication factor for the group metadata internal topics "__consumer_offsets" and "__transaction_state"
# For anything other than development testing, a value greater than 1 is recommended for to ensure availability such as 3.
offsets.topic.replication.factor=3
*/
//实际默认为1，即offsets.topic.replication.factor=1
//动态增加之后如下：
{"version":1,
"partitions":[
{"topic":"__consumer_offsets","partition":0,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":1,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":2,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":3,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":4,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":5,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":6,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":7,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":8,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":9,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":10,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":11,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":12,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":13,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":14,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":15,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":16,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":17,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":18,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":19,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":20,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":21,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":22,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":23,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":24,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":25,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":26,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":27,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":28,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":29,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":30,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":31,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":32,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":33,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":34,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":35,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":36,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":37,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":38,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":39,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":40,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":41,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":42,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":43,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":44,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":45,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":46,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":47,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":48,"replicas":[1,2,3]},
{"topic":"__consumer_offsets","partition":49,"replicas":[1,2,3]}
]}
如下保存为reassign.json文件，然后在shell的kafka的bin目录下执行如下命令
kafka-reassign-partitions.sh --zookeeper localhost:2181 --reassignment-json-file reassign.json --execute
这样，就增加了topic的副本数量；防止topic中的offset所在的broker宕机时候不能提供消费；
如果需要指定自身topic中offset的保存replicas位置（broker位置），则需要将"topic":"__consumer_offsets"改为相应的"topic":“topic_xxx”
我犯的错误是：
Partition reassignment data file is empty
被坑的不清，最后发现是json文件格式中最后一行有一个逗号“，”。这还是在别人发现的问题。特此标注。
如下是原始的reassign.json文件
去掉之后，重新执行
kafka-reassign-partitions.sh --zookeeper localhost:2181 --reassignment-json-file reassign.json --execute
topic的replication设置成功！
