kafka叢集擴容後，新的broker上面不會資料進入這些節點，也就是說，這些節點是空閒的；它只有在建立新的topic時才會參與工作。除非將已有的partition遷移到新的伺服器上面；
所以需要將一些topic的分割槽遷移到新的broker上。

kafka-reassign-partitions.sh是kafka提供的用來重新分配partition和replica到broker上的工具
簡單實現重新分配需要三步：

• 生成分配計劃（generate）
• 執行分配（execute）
• 檢查分配的狀態（verify）

具體操作如下：

1. 生成分配計劃

編寫分配指令碼：
vi topics-to-move.json

內容如下：

{"topics":
    [{"topic":"event_request"}],
    "version": 1
}

執行分配計劃生成指令碼：

kafka-reassign-partitions.sh --zookeeper $ZK_CONNECT --topics-to-move-json-file topics-to-move.json --broker-list "5,6,7,8" --generate

執行結果如下：

[[email protected] topic_reassgin]$ kafka-reassign-partitions.sh --zookeeper $ZK_CONNECT --topics-to-move-json-file topics-to-move.json --broker-list "5,6,7,8" --generate
Current partition replica assignment  #當前分割槽的副本分配

{"version":1,"partitions":[{"topic":"event_request","partition":0,"replicas":[3,4]},{"topic":"event_request","partition":1,"replicas":[4,5]}]}
Proposed partition reassignment configuration #建議的分割槽配置

{"version":1,"partitions":[{"topic":"event_request","partition":0,"replicas":[6,5]},{"topic":"event_request","partition":1,"replicas":[7,6]}]}
 

Proposed partition reassignment configuration 後是根據命令列的指定的brokerlist生成的分割槽分配計劃json格式。將 Proposed partition reassignment configuration的配置copy儲存到一個檔案中 topic-reassignment.json
vi topic-reassignment.json

{"version":1,"partitions":[{"topic":"event_request","partition":0,"replicas":[6,5]},{"topic":"event_request","partition":1,"replicas":[7,6]}]}
 

2. 執行分配（execute）

根據step1 生成的分配計劃配置json檔案topic-reassignment.json，進行topic的重新分配。

kafka-reassign-partitions.sh --zookeeper $ZK_CONNECT --reassignment-json-file topic-reassignment.json --execute

執行前的分割槽分佈：

[[email protected] topic_reassgin]$ le-kafka-topics.sh --describe --topic event_request
Topic:event_request PartitionCount:2    ReplicationFactor:2 Configs:
    Topic: event_request    Partition: 0    Leader: 3   Replicas: 3,4   Isr: 3,4
    Topic: event_request    Partition: 1    Leader: 4   Replicas: 4,5   Isr: 4,5

執行後的分割槽分佈：

[[email protected] topic_reassgin]$ le-kafka-topics.sh --describe --topic event_request
Topic:event_request PartitionCount:2    ReplicationFactor:4 Configs:
    Topic: event_request    Partition: 0    Leader: 3   Replicas: 6,5,3,4   Isr: 3,4
    Topic: event_request    Partition: 1    Leader: 4   Replicas: 7,6,4,5   Isr: 4,5

3. 檢查分配的狀態

檢視分配的狀態：正在進行

[[email protected] topic_reassgin]$ kafka-reassign-partitions.sh --zookeeper $ZK_CONNECT --reassignment-json-file topic-reassignment.json --verify
Status of partition reassignment:
Reassignment of partition [event_request,0] is still in progress
Reassignment of partition [event_request,1] is still in progress
[[email protected] topic_reassgin]$ 

檢視“is still in progress” 狀態時的分割槽，副本分佈狀態：

發現Replicas有4個哦，說明在重新分配的過程中新舊的副本都在進行工作。

[[email protected] topic_reassgin]$ le-kafka-topics.sh --describe --topic event_request
Topic:event_request PartitionCount:2    ReplicationFactor:4 Configs:
    Topic: event_request    Partition: 0    Leader: 3   Replicas: 6,5,3,4   Isr: 3,4
    Topic: event_request    Partition: 1    Leader: 4   Replicas: 7,6,4,5   Isr: 4,5

檢視分配的狀態：分配完成。

[[email protected] topic_reassgin]$ kafka-reassign-partitions.sh --zookeeper $ZK_CONNECT --reassignment-json-file topic-reassignment.json --verify
Status of partition reassignment:
Reassignment of partition [event_request,0] completed successfully
Reassignment of partition [event_request,1] completed successfully

檢視“completed successfully”狀態的分割槽，副本狀態：

已經按照生成的分配計劃正確的完成了分割槽的重新分配。

[[email protected] topic_reassgin]$ le-kafka-topics.sh --describe --topic event_request
Topic:event_request PartitionCount:2    ReplicationFactor:2 Configs:
    Topic: event_request    Partition: 0    Leader: 6   Replicas: 6,5   Isr: 6,5
    Topic: event_request    Partition: 1    Leader: 7   Replicas: 7,6   Isr: 6,7