• 在实际应用中broker可能因为机器，硬件，网络，进程自身等原因挂掉;
• 本章我们来看下一个broker挂掉后整个kafka集群会发生什么事情。

挂掉的broker不是集群的Controller

• 在Kafka集群建立过程分析和KafkaController分析6-Replica状态机我们讲过，KafkaController组件中的ReplicaStateMachine对象在启动时会注册监听BrokerChangeListener事件;
• 当一个broker挂掉后，其在zk的/brokers/ids下面的节点信息将被自动删除;
• ReplicaStateMachine的BrokerChangeListener`将触发：

   val curBrokerIds = currentBrokerList.map(_.toInt).toSet
   val newBrokerIds = curBrokerIds -- controllerContext.liveOrShuttingDownBrokerIds
   val newBrokerInfo = newBrokerIds.map(zkUtils.getBrokerInfo(_))
   val newBrokers = newBrokerInfo.filter(_.isDefined).map(_.get)
   val deadBrokerIds = controllerContext.liveOrShuttingDownBrokerIds -- curBrokerIds
   controllerContext.liveBrokers = curBrokerIds.map(zkUtils.getBrokerInfo(_)).filter(_.isDefined).map(_.get)
newBrokers.foreach(controllerContext.controllerChannelManager.addBroker(_))
              deadBrokerIds.foreach(controllerContext.controllerChannelManager.removeBroker(_))
   if(newBrokerIds.size > 0)
          controller.onBrokerStartup(newBrokerIds.toSeq)
   if(deadBrokerIds.size > 0)
          controller.onBrokerFailure(deadBrokerIds.toSeq)

1. 从zk返回了当前的broker列表信息;
2. val deadBrokerIds = controllerContext.liveOrShuttingDownBrokerIds -- curBrokerIds获取到当前挂掉的broker ids;
3. 更新KafkaControllerContext.liveBrokers;
4. 回调KafkaController.onBrokerFailure(deadBrokerIds.toSeq);

• Broker挂掉的逻辑处理：KafkaController.onBrokerFailure(deadBrokerIds.toSeq)

    val deadBrokersSet = deadBrokers.toSet
    val partitionsWithoutLeader = controllerContext.partitionLeadershipInfo.filter(partitionAndLeader =>
      deadBrokersSet.contains(partitionAndLeader._2.leaderAndIsr.leader) &&
    !deleteTopicManager.isTopicQueuedUpForDeletion(partitionAndLeader._1.topic)).keySet
    partitionStateMachine.handleStateChanges(partitionsWithoutLeader, OfflinePartition)
    partitionStateMachine.triggerOnlinePartitionStateChange()
    var allReplicasOnDeadBrokers = controllerContext.replicasOnBrokers(deadBrokersSet)
    val activeReplicasOnDeadBrokers = allReplicasOnDeadBrokers.filterNot(p => deleteTopicManager.isTopicQueuedUpForDeletion(p.topic))
  replicaStateMachine.handleStateChanges(activeReplicasOnDeadBrokers, OfflineReplica)

1. 先处理KafkacontrollerContext.partitionLeadershipInfo(这里面保存着当前所有topic的各个partition的leader相关信息)，筛选出所有leader为当前挂掉的broker的TopicAndPartiton保存到partitionsWithoutLeader中；
2. 将partitionsWithoutLeader中的partition状态转换成OfflinePartition;
3. 通过partitionStateMachine.triggerOnlinePartitionStateChange()对于上面2中OfflinePartition状态的partition进行重新选主(PartitonStateMachine.electLeaderForPartition);
4. 产生新的LeaderAndIsr Request发送到topic相关的replicas上;
5. 产生新的UpdateMetadata Request发送到各broker上;
6. replicaStateMachine.handleStateChanges(activeReplicasOnDeadBrokers, OfflineReplica): 将相应的replica状态转换为OfflineReplica;
7. 在上面6中的状态转换时会调用controller.removeReplicaFromIsr(topic, partition, replicaId), 生成新的LeaderAndIsr Request, 真正broker挂掉这种情况个人感觉这个调用是多余的,因为在上面的3中新的LeaderAndIsr Request已经发送;

Kafka源码分析-汇总