Kafka集羣擴展以及從新分佈分區

咱們往已經部署好的Kafka集羣裏面添加機器是最正常不過的需求，並且添加起來很是地方便，咱們須要作的事是從已經部署好的Kafka節點中複製相應的配置文件，而後把裏面的broker id修改爲全局惟一的，最後啓動這個節點便可將它加入到現有Kafka集羣中。

　　可是問題來了，新添加的Kafka節點並不會自動地分配數據，因此沒法分擔集羣的負載，除非咱們新建一個topic。可是如今咱們想手動將部分分區移到新添加的Kafka節點上，Kafka內部提供了相關的工具來從新分佈某個topic的分區。在從新分佈topic分區以前，咱們先來看看如今topic的各個分區的分佈位置：

. /bin/kafka-topics .sh --topic iteblog --describe --zookeeper www.iteblog.com:2181 Topic:iteblog PartitionCount:7  ReplicationFactor:2 Configs:    Topic: iteblog  Partition: 0  Leader: 1 Replicas: 1,2 Isr: 1,2    Topic: iteblog  Partition: 1  Leader: 2 Replicas: 2,3 Isr: 2,3    Topic: iteblog  Partition: 2  Leader: 3 Replicas: 3,4 Isr: 3,4    Topic: iteblog  Partition: 3  Leader: 4 Replicas: 4,1 Isr: 4,1    Topic: iteblog  Partition: 4  Leader: 1 Replicas: 1,3 Isr: 1,3    Topic: iteblog  Partition: 5  Leader: 2 Replicas: 2,4 Isr: 2,4    Topic: iteblog  Partition: 6  Leader: 3 Replicas: 3,1 Isr: 3,1

從上面的輸出能夠看出，iteblog主題一共有7個分區，可是咱們broker的個數只有4個，因此會致使某些broker維護更多的分區。如今咱們在現有集羣的基礎上再添加一個Kafka節點，而後使用Kafka自帶的kafka-reassign-partitions.sh工具來從新分佈分區。該工具備三種使用模式：

　　一、generate模式，給定須要從新分配的Topic，自動生成reassign plan（並不執行）
　　二、execute模式，根據指定的reassign plan從新分配Partition
　　三、verify模式，驗證從新分配Partition是否成功

如今咱們須要將原先分佈在broker 1-4節點上的分區從新分佈到broker 1-5節點上，藉助kafka-reassign-partitions.sh工具生成reassign plan，不過咱們先得按照要求定義一個文件，裏面說明哪些topic須要從新分區，文件內容以下：

[iteblog@www.iteblog.com ~]$ cat topics-to-move.json { "topics" : [{ "topic" : "iteblog" }],   "version" :1 }

而後使用kafka-reassign-partitions.sh工具生成reassign plan

[iteblog@www.iteblog.com ~]$ bin/kafka-reassign-partitions.sh --zookeeper www.iteblog.com:2181 --topics-to-move-json-file topics-to-move.json --broker-list "1,2,3,4,5" --generate Current partition replica assignment {"version":1,"partitions":[{"topic":"iteblog","partition":3,"replicas":[4,1]},{"topic":"iteblog","partition":5,"replicas":[2,4]},{"topic":"iteblog","partition":4,"replicas":[1,3]},{"topic":"iteblog","partition":0,"replicas":[1,2]},{"topic":"iteblog","partition":6,"replicas":[3,1]},{"topic":"iteblog","partition":1,"replicas":[2,3]},{"topic":"iteblog","partition":2,"replicas":[3,4]}]} Proposed partition reassignment configuration {"version":1,"partitions":[{"topic":"iteblog","partition":3,"replicas":[3,5]},{"topic":"iteblog","partition":5,"replicas":[5,3]},{"topic":"iteblog","partition":4,"replicas":[4,1]},{"topic":"iteblog","partition":0,"replicas":[5,2]},{"topic":"iteblog","partition":6,"replicas":[1,4]},{"topic":"iteblog","partition":1,"replicas":[1,3]},{"topic":"iteblog","partition":2,"replicas":[2,4]}]} 

Proposed partition reassignment configuration下面生成的就是將分區從新分佈到broker 1-5上的結果。咱們將這些內容保存到名爲result.json文件裏面（文件名不重要，文件格式也不必定要以json爲結尾，只要保證內容是json便可），而後執行這些reassign plan：

[iteblog@www.iteblog.com ~]$ bin/kafka-reassign-partitions.sh --zookeeper www.iteblog.com:2181 --reassignment-json-file result.json --execute Current partition replica assignment {"version":1,"partitions":[{"topic":"iteblog","partition":3,"replicas":[4,1]},{"topic":"iteblog","partition":5,"replicas":[2,4]},{"topic":"iteblog","partition":4,"replicas":[1,3]},{"topic":"iteblog","partition":0,"replicas":[1,2]},{"topic":"iteblog","partition":6,"replicas":[3,1]},{"topic":"iteblog","partition":1,"replicas":[2,3]},{"topic":"iteblog","partition":2,"replicas":[3,4]}]} Save this to use as the --reassignment-json-file option during rollback Successfully started reassignment of partitions {"version":1,"partitions":[{"topic":"iteblog","partition":1,"replicas":[1,3]},{"topic":"iteblog","partition":5,"replicas":[5,3]},{"topic":"iteblog","partition":4,"replicas":[4,1]},{"topic":"iteblog","partition":6,"replicas":[1,4]},{"topic":"iteblog","partition":2,"replicas":[2,4]},{"topic":"iteblog","partition":0,"replicas":[5,2]},{"topic":"iteblog","partition":3,"replicas":[3,5]}]} 

這樣Kafka就在執行reassign plan，咱們能夠校驗reassign plan是否執行完成：

[iteblog@www.iteblog.com ~]$ bin/kafka-reassign-partitions.sh --zookeeper www.iteblog.com:2181 --reassignment-json-file result.json --verify Status of partition reassignment: Reassignment of partition [iteblog,1] completed successfully Reassignment of partition [iteblog,5] is still in progress Reassignment of partition [iteblog,4] completed successfully Reassignment of partition [iteblog,6] completed successfully Reassignment of partition [iteblog,2] completed successfully Reassignment of partition [iteblog,0] is still in progress Reassignment of partition [iteblog,3] completed successfully [iteblog@www.iteblog.com ~]$ bin/kafka-reassign-partitions.sh --zookeeper www.iteblog.com:2181 --reassignment-json-file result.json --verify Status of partition reassignment: Reassignment of partition [iteblog,1] completed successfully Reassignment of partition [iteblog,5] completed successfully Reassignment of partition [iteblog,4] completed successfully Reassignment of partition [iteblog,6] completed successfully Reassignment of partition [iteblog,2] completed successfully Reassignment of partition [iteblog,0] completed successfully Reassignment of partition [iteblog,3] completed successfully 

能夠看出，分區正在Reassignment的狀態是still in progress；若是分區Reassignment完成則completed successfully，而後咱們就能夠看到分區已經按照生成的reassign plan進行，咱們能夠看下topic各個分區如今的分佈狀況：

[iteblog@www.iteblog.com ~]$ ./bin/kafka-topics.sh --topic iteblog --describe --zookeeper www.iteblog.com:2181 Topic:iteblog PartitionCount:7 ReplicationFactor:2 Configs: Topic: iteblog Partition: 0 Leader: 5 Replicas: 5,2 Isr: 2,5 Topic: iteblog Partition: 1 Leader: 1 Replicas: 1,3 Isr: 3,1 Topic: iteblog Partition: 2 Leader: 2 Replicas: 2,4 Isr: 4,2 Topic: iteblog Partition: 3 Leader: 3 Replicas: 3,5 Isr: 3,5 Topic: iteblog Partition: 4 Leader: 1 Replicas: 4,1 Isr: 1,4 Topic: iteblog Partition: 5 Leader: 5 Replicas: 5,3 Isr: 3,5 Topic: iteblog Partition: 6 Leader: 1 Replicas: 1,4 Isr: 1,4 

分區的分佈的確和操做以前不同了，broker 5上已經有分區分佈上去了。可是仔細的同窗應該能夠發現，broker 4上竟然沒有分區的Leader，這確定不是咱們想要的！因此使用kafka-reassign-partitions.sh工具生成的reassign plan只是一個建議，方便你們而已。其實咱們本身徹底能夠編輯一個reassign plan，而後執行它，以下：

{      "version" : 1,      "partitions" : [          {              "topic" : "iteblog" ,              "partition" : 0,              "replicas" : [                  1,                  2              ]          },          {              "topic" : "iteblog" ,              "partition" : 1,              "replicas" : [                  2,                  3              ]          },          {              "topic" : "iteblog" ,              "partition" : 2,              "replicas" : [                  3,                  4              ]          },          {              "topic" : "iteblog" ,              "partition" : 3,              "replicas" : [                  4,                  5              ]          },          {              "topic" : "iteblog" ,              "partition" : 4,              "replicas" : [                  5,                  1              ]          },          {              "topic" : "iteblog" ,              "partition" : 5,              "replicas" : [                  1,                  3              ]          },          {              "topic" : "iteblog" ,              "partition" : 6,              "replicas" : [                  2,                  4              ]          }      ] }

將上面的json數據文件保存到result.json文件中，而後也是執行它：

[iteblog@www.iteblog.com ~]$ bin/kafka-reassign-partitions.sh --zookeeper www.iteblog.com:2181 --reassignment-json-file result.json --execute 

等這個reassign plan執行完，咱們再來看看分區的分佈：

[iteblog@www.iteblog.com ~]$ ./bin/kafka-topics.sh --topic iteblog --describe --zookeeper www.iteblog.com:2181 Topic:iteblog PartitionCount:7 ReplicationFactor:2 Configs: Topic: iteblog Partition: 0 Leader: 1 Replicas: 1,2 Isr: 2,1 Topic: iteblog Partition: 1 Leader: 2 Replicas: 2,3 Isr: 3,2 Topic: iteblog Partition: 2 Leader: 3 Replicas: 3,4 Isr: 4,3 Topic: iteblog Partition: 3 Leader: 4 Replicas: 4,5 Isr: 5,4 Topic: iteblog Partition: 4 Leader: 5 Replicas: 5,1 Isr: 1,5 Topic: iteblog Partition: 5 Leader: 1 Replicas: 1,3 Isr: 3,1 Topic: iteblog Partition: 6 Leader: 2 Replicas: 2,4 Isr: 4,2 

果真已經按照咱們需求分佈了。。