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docs/zh/Kafka分享/Kafka控制器_处理Broker上下线/Kafka控制器_处理Broker上下线.md
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docs/zh/Kafka分享/Kafka控制器_处理Broker上下线/Kafka控制器_处理Broker上下线.md
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# Kafka控制器—处理Broker上下线
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[TOC]
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## 1、前言
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Broker的上下线，除了Broker自身的启停之外呢，Controller还需要对Broker的上下线做元信息的同步等。
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Controller在感知Broker上下线的过程中，主要做了：
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1. 更新本地缓存的元信息；
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2. 下线的关闭连接，新增的增加连接；
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3. 调整下线副本的状态；
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4. 调整需要重新选举Leader的分区；
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5. 进行元信息的同步；
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以上就是Controller做的相关事情，下面我们在细看一下具体的流程。
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## 2、处理上下线
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### 2.1、感知方式
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1. Broker正常上线：Controller感知ZK节点的变化来感知到Broker的上线。
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2. Broker正常下线：Broker主动发送ControlShutdown请求给Controller进行处理后再退出，退出后Controller感知到ZK节点变化后再次进行处理。
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3. Broker异常下线：Controller感知ZK节点的变化来感知Broker的下线。
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那么归结起来，处理上下线就两个流程，一个是通过ZK进行上下线的处理。还有一个是处理ControlShutdown请求来进行Broker下线的处理。
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### 2.2、通过ZK感知Broker上下线
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#### 2.2.1、大体流程
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#### 2.2.2、AddBroker & RemoveBroker
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这块流程非常的简单，这里就不画相关说明图了，我们直接来看一下代码。
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**AddBroker**
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```Java
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def addBroker(broker: Broker): Unit = {
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// be careful here. Maybe the startup() API has already started the request send thread
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brokerLock synchronized {
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if (!brokerStateInfo.contains(broker.id)) {
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addNewBroker(broker)
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startRequestSendThread(broker.id)
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}
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}
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}
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private def addNewBroker(broker: Broker): Unit = {
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// 日志及配置等
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// 创建NetworkClient
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val (networkClient, reconfigurableChannelBuilder) = {
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val channelBuilder = ChannelBuilders.clientChannelBuilder(。。。。。。)
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val reconfigurableChannelBuilder = channelBuilder match {。。。。。。。}
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val selector = new Selector(。。。。。。)
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val networkClient = new NetworkClient(。。。。。。)
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(networkClient, reconfigurableChannelBuilder)
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}
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val threadName = threadNamePrefix match {
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case None => s"Controller-${config.brokerId}-to-broker-${broker.id}-send-thread"
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case Some(name) => s"$name:Controller-${config.brokerId}-to-broker-${broker.id}-send-thread"
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}
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// metrics
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// 创建请求网络IO处理线程
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val requestThread = new RequestSendThread(config.brokerId, controllerContext, messageQueue, networkClient,
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brokerNode, config, time, requestRateAndQueueTimeMetrics, stateChangeLogger, threadName)
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requestThread.setDaemon(false)
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// metrics
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// 缓存创建的信息
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brokerStateInfo.put(broker.id, ControllerBrokerStateInfo(networkClient, brokerNode, messageQueue,
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requestThread, queueSizeGauge, requestRateAndQueueTimeMetrics, reconfigurableChannelBuilder))
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}
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```
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**RemoveBroker**
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```Java
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def removeBroker(brokerId: Int): Unit = {
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brokerLock synchronized {
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removeExistingBroker(brokerStateInfo(brokerId))
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}
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}
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private def removeExistingBroker(brokerState: ControllerBrokerStateInfo): Unit = {
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try {
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// 关闭相关新建的对象
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brokerState.reconfigurableChannelBuilder.foreach(config.removeReconfigurable)
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brokerState.requestSendThread.shutdown()
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brokerState.networkClient.close()
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brokerState.messageQueue.clear()
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removeMetric(QueueSizeMetricName, brokerMetricTags(brokerState.brokerNode.id))
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removeMetric(RequestRateAndQueueTimeMetricName, brokerMetricTags(brokerState.brokerNode.id))
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brokerStateInfo.remove(brokerState.brokerNode.id)
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} catch {
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case e: Throwable => error("Error while removing broker by the controller", e)
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}
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}
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```
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#### 2.2.3、处理Broker上线(onBrokerStartup)
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##### 2.2.3.1、大体流程
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##### 2.2.3.2、相关代码
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```Java
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private def onBrokerStartup(newBrokers: Seq[Int]): Unit = {
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info(s"New broker startup callback for ${newBrokers.mkString(",")}")
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newBrokers.foreach(controllerContext.replicasOnOfflineDirs.remove)
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val newBrokersSet = newBrokers.toSet
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val existingBrokers = controllerContext.liveOrShuttingDownBrokerIds -- newBrokers
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// 发送空的元信息到已存在的broker上
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sendUpdateMetadataRequest(existingBrokers.toSeq, Set.empty)
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// 发送完整的元信息到新增的Broker上
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sendUpdateMetadataRequest(newBrokers, controllerContext.partitionLeadershipInfo.keySet)
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// 或者到所有在新增Broker上的副本
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val allReplicasOnNewBrokers = controllerContext.replicasOnBrokers(newBrokersSet)
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// 变更副本状态
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replicaStateMachine.handleStateChanges(allReplicasOnNewBrokers.toSeq, OnlineReplica)
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// 变更分区状态
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partitionStateMachine.triggerOnlinePartitionStateChange()
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// 恢复迁移
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maybeResumeReassignments { (_, assignment) =>
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assignment.targetReplicas.exists(newBrokersSet.contains)
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}
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// 恢复删除
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val replicasForTopicsToBeDeleted = allReplicasOnNewBrokers.filter(p => topicDeletionManager.isTopicQueuedUpForDeletion(p.topic))
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if (replicasForTopicsToBeDeleted.nonEmpty) {
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// 日志
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topicDeletionManager.resumeDeletionForTopics(replicasForTopicsToBeDeleted.map(_.topic))
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}
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// 注册监听
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registerBrokerModificationsHandler(newBrokers)
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}
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```
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#### 2.2.4、处理Broker下线(onBrokerFailure)
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##### 2.2.4.1、大体流程
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##### 2.2.4.2、相关代码
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```Java
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private def onBrokerFailure(deadBrokers: Seq[Int]): Unit = {
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info(s"Broker failure callback for ${deadBrokers.mkString(",")}")
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// 缓存中移除dead-broker
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// 获取到dead-broker上相关的副本
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val allReplicasOnDeadBrokers = controllerContext.replicasOnBrokers(deadBrokers.toSet)
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// 相关副本状态处理
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onReplicasBecomeOffline(allReplicasOnDeadBrokers)
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// 取消Broker节点被修改的事件的监听
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unregisterBrokerModificationsHandler(deadBrokers)
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}
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private def onReplicasBecomeOffline(newOfflineReplicas: Set[PartitionAndReplica]): Unit = {
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// 被影响的副本中，区分是要被删除的和不用被删除的
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val (newOfflineReplicasForDeletion, newOfflineReplicasNotForDeletion) =
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newOfflineReplicas.partition(p => topicDeletionManager.isTopicQueuedUpForDeletion(p.topic))
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// 获取broker下线后将无leader的分区
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val partitionsWithoutLeader = controllerContext.partitionLeadershipInfo.filter(partitionAndLeader =>
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!controllerContext.isReplicaOnline(partitionAndLeader._2.leaderAndIsr.leader, partitionAndLeader._1) &&
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!topicDeletionManager.isTopicQueuedUpForDeletion(partitionAndLeader._1.topic)).keySet
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// 无leader的分区进行状态切换，及leader选举
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partitionStateMachine.handleStateChanges(partitionsWithoutLeader.toSeq, OfflinePartition)
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partitionStateMachine.triggerOnlinePartitionStateChange()
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// 不删除的副本的状态切换
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replicaStateMachine.handleStateChanges(newOfflineReplicasNotForDeletion.toSeq, OfflineReplica)
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if (newOfflineReplicasForDeletion.nonEmpty) {
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// 需要删除的副本的Topic标记删除失败
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topicDeletionManager.failReplicaDeletion(newOfflineReplicasForDeletion)
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}
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// 如果没有leader变化的分区，则对所有broker进行空的元信息同步
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if (partitionsWithoutLeader.isEmpty) {
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sendUpdateMetadataRequest(controllerContext.liveOrShuttingDownBrokerIds.toSeq, Set.empty)
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}
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}
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```
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### 2.3、Broker主动下线——处理ControlShutdown请求
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#### 2.3.1、大体流程
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#### 2.3.2、相关代码
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```Java
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// 逐层调用
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def handleControlledShutdownRequest(request: RequestChannel.Request): Unit = {
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//////
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}
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private def processControlledShutdown(id: Int, brokerEpoch: Long, controlledShutdownCallback: Try[Set[TopicPartition]] => Unit): Unit = {
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//////
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}
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// 执行下线请求的处理
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private def doControlledShutdown(id: Int, brokerEpoch: Long): Set[TopicPartition] = {
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if (!isActive) {
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throw new ControllerMovedException("Controller moved to another broker. Aborting controlled shutdown")
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}
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// epoch值异常，抛出异常。broker不存在，抛出异常等
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// 加入shuttingdown中
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controllerContext.shuttingDownBrokerIds.add(id)
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// 获取本次broker下线影响到的分区
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val partitionsToActOn = controllerContext.partitionsOnBroker(id).filter { partition =>
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controllerContext.partitionReplicaAssignment(partition).size > 1 &&
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controllerContext.partitionLeadershipInfo.contains(partition) &&
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!topicDeletionManager.isTopicQueuedUpForDeletion(partition.topic)
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}
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// 分区区分是leader分区还是follower分区
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val (partitionsLedByBroker, partitionsFollowedByBroker) = partitionsToActOn.partition { partition =>
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controllerContext.partitionLeadershipInfo(partition).leaderAndIsr.leader == id
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}
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// leader分区进行leader重新选举等
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partitionStateMachine.handleStateChanges(partitionsLedByBroker.toSeq, OnlinePartition, Some(ControlledShutdownPartitionLeaderElectionStrategy))
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try {
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brokerRequestBatch.newBatch()
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partitionsFollowedByBroker.foreach { partition =>
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brokerRequestBatch.addStopReplicaRequestForBrokers(Seq(id), partition, deletePartition = false)
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}
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brokerRequestBatch.sendRequestsToBrokers(epoch)
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} catch {
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case e: IllegalStateException =>
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handleIllegalState(e)
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}
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// Follower分区的副本，调整状态为OfflineReplica
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replicaStateMachine.handleStateChanges(partitionsFollowedByBroker.map(partition =>
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PartitionAndReplica(partition, id)).toSeq, OfflineReplica)
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def replicatedPartitionsBrokerLeads() = {
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// 获取获取落在broker上的leader分区
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}
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replicatedPartitionsBrokerLeads().toSet
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}
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```
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## 3、常见问题
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### 3.1、元信息同步的范围
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准守的基本原则：
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1. Topic的Leader及Follower的信息没有变化时，基本上只需要发送UpdateMetadata请求，会发送到所有的Broker。
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2. 如果Topic的Leader或Follower的信息发生变化了，则会对迁移到的相关Broker发送LeaderAndIsr请求以更新副本之间的同步状态。此外还会对整个集群的Broker发送UpdateMetadata请求，从而保证集群每个Broker上缓存的元信息是一致的。
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3. 牵扯到副本的暂停副本同步的时候，会对相关的Broker发送StopReplica的请求。
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此外呢，我们在代码中也可以看到，有时候还会发送空的UpdateMetadata请求到Broker。
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这个的主要原因是：
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UpdateMetadata请求，除了同步Topic元信息之外，还会同步集群的Broker信息。所以最后一个原则：
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- 即使Topic都没有变化，但是Broker发生变化的时候，也会发送UpdateMetadata请求。
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### 3.2、元信息同步性能
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上述的操作的主流程上，除了和ZK可能存在部分的网络IO之外，不会存在和集群其他的Broker的直接的网络IO。
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因此，基本上秒级或者更短的时间可处理完。
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## 4、总结
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本次分享了Broker上下线过程中，Controller需要做的事情，然后对常见的问题进行了讨论。以上就是本次分享的全部内容，谢谢大家。
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