1. controller 选举
每个kafka集群里的controller在某一个时刻只能由一个Broker担任，这个Broker是由集群里的所有Broker选举出来的， 随着时间的推移，Controller可能易主。
选举原理：
选举时，每个Broker都尝试向zookeeper写入/controller，但只能有一个Broker成功，这个Broker节点就是Controller所在的节点，同时每个Broker会向/controller节点注册监听器，这样当原来Controller所在的Broker挂掉后其余Broker就能感知到，以便触发新的选举流程。
选举时机：
- 集群启动
- /controller 节点消失
- /controller节点发生变更
Controller的主要代码在KafkaController.scala文件中，首先看下KafkaController类的重要字段。
class KafkaController(val config: KafkaConfig, // Kafka配置信息
zkClient: KafkaZkClient, // zk客户端，封装了对zookeeper的所有操作
time: Time, // 时间工具类
metrics: Metrics, // 实现指标监控服务(如创建监控指标)的工具类
initialBrokerInfo: BrokerInfo, // Broker节点信息
initialBrokerEpoch: Long, // Broker Epoch值，用于隔离老Controller发送的请求
tokenManager: DelegationTokenManager, // 实现Delegation token管理的工具类
threadNamePrefix: Option[String] = None // Controller事件处理线程名字前缀
) extends Logging with KafkaMetricsGroup {
// 集群元数据类，保存集群所有元数据
val controllerContext = new ControllerContext
// 线程调度器，当前唯一负责定期执行Leader重选举
private[controller] val kafkaScheduler = new KafkaScheduler(1)
// Controller事件管理器，负责管理事件处理线程
private[controller] val eventManager = new ControllerEventManager(config.brokerId,
controllerContext.stats.rateAndTimeMetrics, _ => updateMetrics(), () => maybeResign())
// topic删除管理器
val topicDeletionManager = new TopicDeletionManager(this, eventManager, zkClient)
private val brokerRequestBatch = new ControllerBrokerRequestBatch(this, stateChangeLogger)
// 副本状态机，负责副本状态转换
val replicaStateMachine = new ReplicaStateMachine(config, stateChangeLogger, controllerContext, topicDeletionManager, zkClient, mutable.Map.empty, new ControllerBrokerRequestBatch(this, stateChangeLogger))
// 分区状态机，负责分区状态转换
val partitionStateMachine = new PartitionStateMachine(config, stateChangeLogger, controllerContext, zkClient, mutable.Map.empty, new ControllerBrokerRequestBatch(this, stateChangeLogger))
partitionStateMachine.setTopicDeletionManager(topicDeletionManager)
// Controller节点ZooKeeper监听器
private val controllerChangeHandler = new ControllerChangeHandler(this, eventManager)
// Broker数量ZooKeeper监听器
private val brokerChangeHandler = new BrokerChangeHandler(this, eventManager)
// Broker信息变更ZooKeeper监听器集合
private val brokerModificationsHandlers: mutable.Map[Int, BrokerModificationsHandler] = mutable.Map.empty
// 主题数量ZooKeeper监听器
private val topicChangeHandler = new TopicChangeHandler(this, eventManager)
// 主题删除ZooKeeper监听器
private val topicDeletionHandler = new TopicDeletionHandler(this, eventManager)
// 主题分区变更ZooKeeper监听器
private val partitionModificationsHandlers: mutable.Map[String, PartitionModificationsHandler] = mutable.Map.empty
// 主题分区重分配ZooKeeper监听器
private val partitionReassignmentHandler = new PartitionReassignmentHandler(this, eventManager)
// Preferred Leader选举ZooKeeper监听器
private val preferredReplicaElectionHandler = new PreferredReplicaElectionHandler(this, eventManager)
// ISR副本集合变更ZooKeeper监听器
private val isrChangeNotificationHandler = new IsrChangeNotificationHandler(this, eventManager)
// 日志路径变更ZooKeeper监听器
private val logDirEventNotificationHandler = new LogDirEventNotificationHandler(this, eventManager)
// 当前Controller所在Broker Id
@volatile private var activeControllerId = -1
// 离线分区总数
@volatile private var offlinePartitionCount = 0
// 满足Preferred Leader选举条件的总分区数
@volatile private var preferredReplicaImbalanceCount = 0
// 总主题数
@volatile private var globalTopicCount = 0
// 总分区数
@volatile private var globalPartitionCount = 0
...
}KafkaController的启动在KafkaServer的startup方法中完成的。
// KafkaServer.scala
kafkaController = new KafkaController(config, zkClient, time, metrics, brokerInfo, brokerEpoch, tokenManager, threadNamePrefix)
kafkaController.startup()def startup() = {
// registerStateChangeHandler用于session过期后触发重新选举
zkClient.registerStateChangeHandler(new StateChangeHandler {
override val name: String = StateChangeHandlers.ControllerHandler
override def afterInitializingSession(): Unit = {
eventManager.put(RegisterBrokerAndReelect)
}
override def beforeInitializingSession(): Unit = {
val expireEvent = new Expire
eventManager.clearAndPut(expireEvent)
// 阻塞等待时间被处理结束,session过期触发重新选举,必须等待选举这个时间完成Controller才能正常工作
expireEvent.waitUntilProcessingStarted()
}
})
// 将Startup放入eventManager
eventManager.put(Startup)
// 启动eventManager后台线程开始选举
eventManager.start()
}KafkaController启动时会向eventManager中发送Startup事件消息，Startup消息的具体处理逻辑在Startup的process方法中。
case object Startup extends ControllerEvent {
def state = ControllerState.ControllerChange
override def process(): Unit = {
// 注册ControllerChangeHandler ZooKeeper监听器
zkClient.registerZNodeChangeHandlerAndCheckExistence(controllerChangeHandler)
// 选举controller
elect()
}
}process 方法中会调用elect方法。elect的主要流程如下：
private def elect(): Unit = {
// 获取当前Controller所在Broker的序号，如果Controller不存在，显式标记为-1
activeControllerId = zkClient.getControllerId.getOrElse(-1)
// 如果当前Controller已经选出来了，直接返回即可
if (activeControllerId != -1) {
debug(s"Broker $activeControllerId has been elected as the controller, so stopping the election process.")
return
}
try {
// 创建临时节点,让本节点参与选举
val (epoch, epochZkVersion) = zkClient.registerControllerAndIncrementControllerEpoch(config.brokerId)
controllerContext.epoch = epoch
controllerContext.epochZkVersion = epochZkVersion
activeControllerId = config.brokerId
info(s"${config.brokerId} successfully elected as the controller. Epoch incremented to ${controllerContext.epoch} " +
s"and epoch zk version is now ${controllerContext.epochZkVersion}")
// 执行当选Controller的后续逻辑
onControllerFailover()
} catch {
case e: ControllerMovedException =>
maybeResign()
if (activeControllerId != -1)
debug(s"Broker $activeControllerId was elected as controller instead of broker ${config.brokerId}", e)
else
warn("A controller has been elected but just resigned, this will result in another round of election", e)
case t: Throwable =>
error(s"Error while electing or becoming controller on broker ${config.brokerId}. " +
s"Trigger controller movement immediately", t)
triggerControllerMove()
}
}elect方法会尝试在zookeeper中创建/controller临时节点，因此只有Controller所在的节点才会执行onControllerFailover方法，其他节点都会进入异常处理。
private def onControllerFailover() {
info("Registering handlers")
// 注册各种监听器
val childChangeHandlers = Seq(brokerChangeHandler, topicChangeHandler, topicDeletionHandler, logDirEventNotificationHandler,
isrChangeNotificationHandler)
childChangeHandlers.foreach(zkClient.registerZNodeChildChangeHandler)
val nodeChangeHandlers = Seq(preferredReplicaElectionHandler, partitionReassignmentHandler)
nodeChangeHandlers.foreach(zkClient.registerZNodeChangeHandlerAndCheckExistence)
info("Deleting log dir event notifications")
zkClient.deleteLogDirEventNotifications(controllerContext.epochZkVersion)
info("Deleting isr change notifications")
zkClient.deleteIsrChangeNotifications(controllerContext.epochZkVersion)
info("Initializing controller context")
initializeControllerContext()
info("Fetching topic deletions in progress")
val (topicsToBeDeleted, topicsIneligibleForDeletion) = fetchTopicDeletionsInProgress()
info("Initializing topic deletion manager")
// 初始化topic删除管理器
topicDeletionManager.init(topicsToBeDeleted, topicsIneligibleForDeletion)
info("Sending update metadata request")
// 发送更新集群元数据请求
sendUpdateMetadataRequest(controllerContext.liveOrShuttingDownBrokerIds.toSeq, Set.empty)
// 启动副本状态机
replicaStateMachine.startup()
// 启动分区状态机
partitionStateMachine.startup()
info(s"Ready to serve as the new controller with epoch $epoch")
maybeTriggerPartitionReassignment(controllerContext.partitionsBeingReassigned.keySet)
topicDeletionManager.tryTopicDeletion()
val pendingPreferredReplicaElections = fetchPendingPreferredReplicaElections()
onPreferredReplicaElection(pendingPreferredReplicaElections, ZkTriggered)
info("Starting the controller scheduler")
kafkaScheduler.startup()
if (config.autoLeaderRebalanceEnable) {
scheduleAutoLeaderRebalanceTask(delay = 5, unit = TimeUnit.SECONDS)
}
if (config.tokenAuthEnabled) {
info("starting the token expiry check scheduler")
tokenCleanScheduler.startup()
tokenCleanScheduler.schedule(name = "delete-expired-tokens",
fun = () => tokenManager.expireTokens,
period = config.delegationTokenExpiryCheckIntervalMs,
unit = TimeUnit.MILLISECONDS)
}
}/controller节点变更会触发重新选举，具体方法为maybeResign。
private def maybeResign(): Unit = {
// 判断Controller是否发生变更
val wasActiveBeforeChange = isActive
// 注册ControllerChangeHandler监听器
zkClient.registerZNodeChangeHandlerAndCheckExistence(controllerChangeHandler)
activeControllerId = zkClient.getControllerId.getOrElse(-1)
if (wasActiveBeforeChange && !isActive) {
// 执行卸任逻辑
onControllerResignation()
}
}onControllerResignation复杂执行卸任逻辑。
private def onControllerResignation() {
debug("Resigning")
// de-register listeners
// 取消ZooKeeper监听器的注册
zkClient.unregisterZNodeChildChangeHandler(isrChangeNotificationHandler.path)
zkClient.unregisterZNodeChangeHandler(partitionReassignmentHandler.path)
zkClient.unregisterZNodeChangeHandler(preferredReplicaElectionHandler.path)
zkClient.unregisterZNodeChildChangeHandler(logDirEventNotificationHandler.path)
unregisterBrokerModificationsHandler(brokerModificationsHandlers.keySet)
// reset topic deletion manager
topicDeletionManager.reset()
// shutdown leader rebalance scheduler
// 关闭Kafka线程调度器，其实就是取消定期的Leader重选举
kafkaScheduler.shutdown()
// 将统计字段全部清0
offlinePartitionCount = 0
preferredReplicaImbalanceCount = 0
globalTopicCount = 0
globalPartitionCount = 0
// stop token expiry check scheduler
// 关闭Token过期检查调度器
if (tokenCleanScheduler.isStarted)
tokenCleanScheduler.shutdown()
// de-register partition ISR listener for on-going partition reassignment task
// 取消分区重分配监听器的注册
unregisterPartitionReassignmentIsrChangeHandlers()
// shutdown partition state machine
// 关闭分区状态机
partitionStateMachine.shutdown()
// 取消主题变更监听器的注册
zkClient.unregisterZNodeChildChangeHandler(topicChangeHandler.path)
// 取消分区变更监听器的注册
unregisterPartitionModificationsHandlers(partitionModificationsHandlers.keys.toSeq)
// 取消主题删除监听器的注册
zkClient.unregisterZNodeChildChangeHandler(topicDeletionHandler.path)
// shutdown replica state machine
// 关闭副本状态机
replicaStateMachine.shutdown()
// 取消Broker变更监听器的注册
zkClient.unregisterZNodeChildChangeHandler(brokerChangeHandler.path)
// 清空controller元数据
controllerContext.resetContext()
info("Resigned")
}2. controller 作用：
Controller是kafka一个非常重要的组件。主要的功能包括集群管理和主题管理。下面就结合源代码介绍下集群管理中的broke信息管理如何实现。
broker信息变更主要依靠BrokerModificationsHandler实现，当broker信息变更时会向eventManager发送BrokerModifications消息。
class BrokerModificationsHandler(controller: KafkaController, eventManager: ControllerEventManager, brokerId: Int) extends ZNodeChangeHandler {
override val path: String = BrokerIdZNode.path(brokerId)
override def handleDataChange(): Unit = {
eventManager.put(controller.BrokerModifications(brokerId))
}
}broker信息变更的处理逻辑在BrokerModifications的process方法中。
case class BrokerModifications(brokerId: Int) extends ControllerEvent {
override def state: ControllerState = ControllerState.BrokerChange
override def process(): Unit = {
if (!isActive) return
// 从zookeeper中获取获取目标Broker的详细数据。
val newMetadata = zkClient.getBroker(brokerId)
// 从元数据缓存中获得目标Broker的详细数据
val oldMetadata = controllerContext.liveBrokers.find(_.id == brokerId)
// 如果两者不相等，说明Broker数据发生了变更
if (newMetadata.nonEmpty && oldMetadata.nonEmpty && newMetadata.map(_.endPoints) != oldMetadata.map(_.endPoints)) {
info(s"Updated broker: ${newMetadata.get}")
// 更新元数据
controllerContext.updateBrokerMetadata(oldMetadata, newMetadata)
// 向其他Broker同步新的元数据
onBrokerUpdate(brokerId)
}
}
}private def onBrokerUpdate(updatedBrokerId: Int) {
info(s"Broker info update callback for $updatedBrokerId")
// 给集群所有Broker发送更新元数据的请求UpdateMetadataRequest
sendUpdateMetadataRequest(controllerContext.liveOrShuttingDownBrokerIds.toSeq, Set.empty)
}
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