什么是RPC通信
RPC是指远程过程调用，也就是说两台服务器A,B，一个应用部署在A服务器上，想要调用B服务器上应用提供的函数或者方法，由于不在同一个内存空间，不能直接调用，需要通过网络来表达调用的语义和传达调用的数据。
SparkRPC通信
Spark1.6+推出以RPCEnv,RPCEndopoint，RPCEndpointRef为核心的新型架构下的通信方式。具体实现方式又Akka和Netty两种方式。kka是基于Scala的Actor的分布式消息通信系统，Netty是由JBOSS提供的一个java开源框架。Netty提供异步的、事件驱动的网络应用程序框架和工具，用以快速开发高性能、高可靠性的网络服务器和客户端程序。
RPC
spark 启动消息通信基本过程
首先启动Spark会执行sbin/start-all.sh
# Start all spark daemons.
# Starts the master on this node.
# Starts a worker on each node specified in conf/slaves
sbin="`dirname "$0"`"
sbin="`cd "$sbin"; pwd`"
TACHYON_STR=""
while (( "$#" )); do
case $1 in
--with-tachyon)
TACHYON_STR="--with-tachyon"
;;
esac
shift
done
# Load the Spark configuration
. "$sbin/spark-config.sh"
# Start Master
"$sbin"/start-master.sh $TACHYON_STR
# Start Workers
"$sbin"/start-slaves.sh $TACHYON_STR
通过查看start-master.sh，发现先启动master，再启动worker。
"$sbin"/spark-daemon.sh start org.apache.spark.deploy.master.Master 1 \
--ip $SPARK_MASTER_IP --port $SPARK_MASTER_PORT --webui-port $SPARK_MASTER_WEBUI_PORT \
$ORIGINAL_ARGS
最终执行spark-daemon.sh start org.apache.spark.deploy.master.Master
接下来我们来看Master的main方法
private[deploy] object Master extends Logging {
val SYSTEM_NAME = "sparkMaster"
val ENDPOINT_NAME = "Master"
def main(argStrings: Array[String]) {
Thread.setDefaultUncaughtExceptionHandler(new SparkUncaughtExceptionHandler(
exitOnUncaughtException = false))
Utils.initDaemon(log)
val conf = new SparkConf
val args = new MasterArguments(argStrings, conf)
val (rpcEnv, _, _) =
//将脚本中传入的RpcEnv和host,port启动Master
startRpcEnvAndEndpoint(args.host, args.port, args.webUiPort, conf)
rpcEnv.awaitTermination()
}
/**
* Start the Master and return a three tuple of:
* (1) The Master RpcEnv
* (2) The web UI bound port
* (3) The REST server bound port, if any
*/
def startRpcEnvAndEndpoint(
host: String,
port: Int,
webUiPort: Int,
conf: SparkConf): (RpcEnv, Int, Option[Int]) = {
val securityMgr = new SecurityManager(conf)
val rpcEnv = RpcEnv.create(SYSTEM_NAME, host, port, conf, securityMgr)
val masterEndpoint = rpcEnv.setupEndpoint(ENDPOINT_NAME,
new Master(rpcEnv, rpcEnv.address, webUiPort, securityMgr, conf))
//master终端点send a message to the corresponding [[RpcEndpoint]]，这个RpcEndpoint就是Master
val portsResponse = masterEndpoint.askSync[BoundPortsResponse](BoundPortsRequest)
(rpcEnv, portsResponse.webUIPort, portsResponse.restPort)
}
创建消息通信框架使用的RpcEnv,终端点MasterEndpoint
之后Master回再receiveAndReply方法进行回复
override def receiveAndReply(context: RpcCallContext): PartialFunction[Any, Unit] = {
case RequestSubmitDriver(description) =>
if (state != RecoveryState.ALIVE) {
val msg = s"${Utils.BACKUP_STANDALONE_MASTER_PREFIX}: $state. " +
"Can only accept driver submissions in ALIVE state."
context.reply(SubmitDriverResponse(self, false, None, msg))
} else {
logInfo("Driver submitted " + description.command.mainClass)
val driver = createDriver(description)
persistenceEngine.addDriver(driver)
waitingDrivers += driver
drivers.add(driver)
schedule()
// TODO: It might be good to instead have the submission client poll the master to determine
// the current status of the driver. For now it's simply "fire and forget".
context.reply(SubmitDriverResponse(self, true, Some(driver.id),
s"Driver successfully submitted as ${driver.id}"))
}
case RequestKillDriver(driverId) =>
if (state != RecoveryState.ALIVE) {
val msg = s"${Utils.BACKUP_STANDALONE_MASTER_PREFIX}: $state. " +
s"Can only kill drivers in ALIVE state."
context.reply(KillDriverResponse(self, driverId, success = false, msg))
} else {
logInfo("Asked to kill driver " + driverId)
val driver = drivers.find(_.id == driverId)
driver match {
case Some(d) =>
if (waitingDrivers.contains(d)) {
waitingDrivers -= d
self.send(DriverStateChanged(driverId, DriverState.KILLED, None))
} else {
// We just notify the worker to kill the driver here. The final bookkeeping occurs
// on the return path when the worker submits a state change back to the master
// to notify it that the driver was successfully killed.
d.worker.foreach { w =>
w.endpoint.send(KillDriver(driverId))
}
}
// TODO: It would be nice for this to be a synchronous response
val msg = s"Kill request for $driverId submitted"
logInfo(msg)
context.reply(KillDriverResponse(self, driverId, success = true, msg))
case None =>
val msg = s"Driver $driverId has already finished or does not exist"
logWarning(msg)
context.reply(KillDriverResponse(self, driverId, success = false, msg))
}
}
case RequestDriverStatus(driverId) =>
if (state != RecoveryState.ALIVE) {
val msg = s"${Utils.BACKUP_STANDALONE_MASTER_PREFIX}: $state. " +
"Can only request driver status in ALIVE state."
context.reply(
DriverStatusResponse(found = false, None, None, None, Some(new Exception(msg))))
} else {
(drivers ++ completedDrivers).find(_.id == driverId) match {
case Some(driver) =>
context.reply(DriverStatusResponse(found = true, Some(driver.state),
driver.worker.map(_.id), driver.worker.map(_.hostPort), driver.exception))
case None =>
context.reply(DriverStatusResponse(found = false, None, None, None, None))
}
}
case RequestMasterState =>
context.reply(MasterStateResponse(
address.host, address.port, restServerBoundPort,
workers.toArray, apps.toArray, completedApps.toArray,
drivers.toArray, completedDrivers.toArray, state))
case BoundPortsRequest =>
context.reply(BoundPortsResponse(address.port, webUi.boundPort, restServerBoundPort))
case RequestExecutors(appId, requestedTotal) =>
context.reply(handleRequestExecutors(appId, requestedTotal))
case KillExecutors(appId, executorIds) =>
val formattedExecutorIds = formatExecutorIds(executorIds)
context.reply(handleKillExecutors(appId, formattedExecutorIds))
}
Worker启动与Master类似
def main(argStrings: Array[String]) {
Thread.setDefaultUncaughtExceptionHandler(new SparkUncaughtExceptionHandler(
exitOnUncaughtException = false))
Utils.initDaemon(log)
val conf = new SparkConf
val args = new WorkerArguments(argStrings, conf)
val rpcEnv = startRpcEnvAndEndpoint(args.host, args.port, args.webUiPort, args.cores,
args.memory, args.masters, args.workDir, conf = conf)
// With external shuffle service enabled, if we request to launch multiple workers on one host,
// we can only successfully launch the first worker and the rest fails, because with the port
// bound, we may launch no more than one external shuffle service on each host.
// When this happens, we should give explicit reason of failure instead of fail silently. For
// more detail see SPARK-20989.
val externalShuffleServiceEnabled = conf.getBoolean("spark.shuffle.service.enabled", false)
val sparkWorkerInstances = scala.sys.env.getOrElse("SPARK_WORKER_INSTANCES", "1").toInt
require(externalShuffleServiceEnabled == false || sparkWorkerInstances <= 1,
"Starting multiple workers on one host is failed because we may launch no more than one " +
"external shuffle service on each host, please set spark.shuffle.service.enabled to " +
"false or set SPARK_WORKER_INSTANCES to 1 to resolve the conflict.")
rpcEnv.awaitTermination()
}
def startRpcEnvAndEndpoint(
host: String,
port: Int,
webUiPort: Int,
cores: Int,
memory: Int,
masterUrls: Array[String],
workDir: String,
workerNumber: Option[Int] = None,
conf: SparkConf = new SparkConf): RpcEnv = {
// The LocalSparkCluster runs multiple local sparkWorkerX RPC Environments
val systemName = SYSTEM_NAME + workerNumber.map(_.toString).getOrElse("")
val securityMgr = new SecurityManager(conf)
val rpcEnv = RpcEnv.create(systemName, host, port, conf, securityMgr)
val masterAddresses = masterUrls.map(RpcAddress.fromSparkURL(_))
rpcEnv.setupEndpoint(ENDPOINT_NAME, new Worker(rpcEnv, webUiPort, cores, memory,
masterAddresses, ENDPOINT_NAME, workDir, conf, securityMgr))
rpcEnv
}
1.worker节点向master节点发送注册消息。
2.注册成功后，返回成功消息或者失败消息。
3.worker定时向master发送心跳。
如图：
Spark启动消息通信
a)、当master启动后，随之启动各worker，worker启动时会创建通信环境RpcEnv和终端点Endpoint，并向Master发送注册Worker的消息RegisterWorker。
由于Worker可能需要注册多个Master（HA），在Worker类的tryRegisterAllMasters方法中创建注册线程池。把需要注册的请求，放入线程池中，然后通过启动线程池来注册。
b)、注册过程：
获取master终端引用，调用registerWithMaster
//通过构造方法Worker调用onStart
override def onStart() {
assert(!registered)
logInfo("Starting Spark worker %s:%d with %d cores, %s RAM".format(
host, port, cores, Utils.megabytesToString(memory)))
logInfo(s"Running Spark version ${org.apache.spark.SPARK_VERSION}")
logInfo("Spark home: " + sparkHome)
createWorkDir()
shuffleService.startIfEnabled()
webUi = new WorkerWebUI(this, workDir, webUiPort)
webUi.bind()
workerWebUiUrl = s"http://$publicAddress:${webUi.boundPort}"
registerWithMaster() //向Master进行注册Worker
metricsSystem.registerSource(workerSource)
metricsSystem.start()
// Attach the worker metrics servlet handler to the web ui after the metrics system is started.
metricsSystem.getServletHandlers.foreach(webUi.attachHandler)
}
//Spark使用ZK来实现Master的HA，首先会创建一个线程池 registerMasterThreadPool，注册一个阻塞的Action，这个线城池要实现向所有master进行注册。
private def tryRegisterAllMasters(): Array[JFuture[_]] = {
masterRpcAddresses.map { masterAddress =>
registerMasterThreadPool.submit(new Runnable {
override def run(): Unit = {
try {
logInfo("Connecting to master " + masterAddress + "...")
val masterEndpoint = rpcEnv.setupEndpointRef(masterAddress, Master.ENDPOINT_NAME)
//发送注册RegisterWorker sendRegisterMessageToMaster(masterEndpoint)
} catch {
case ie: InterruptedException => // Cancelled
case NonFatal(e) => logWarning(s"Failed to connect to master $masterAddress", e)
}
}
})
}
}
//Ask方法定义为：
/**
* Send a message to the corresponding [[RpcEndpoint.receiveAndReply)]] and return a [[Future]] to
* receive the reply within a default timeout.
*
* This method only sends the message once and never retries.
*/
def ask[T: ClassTag](message: Any): Future[T] = ask(message, defaultAskTimeout)
private def registerWithMaster(masterEndpoint: RpcEndpointRef): Unit = {
masterEndpoint.ask[RegisterWorkerResponse](RegisterWorker(
workerId, host, port, self, cores, memory, workerWebUiUrl))
.onComplete {
// This is a very fast action so we can use "ThreadUtils.sameThread"
case Success(msg) =>
Utils.tryLogNonFatalError {
handleRegisterResponse(msg)
}
case Failure(e) =>
logError(s"Cannot register with master: ${masterEndpoint.address}", e)
System.exit(1)
}(ThreadUtils.sameThread)
}
c) Master收到消息后，需要对Worker发送的信息进行验证、记录。如果注册成功，则发送RegisteredWorker消息给对应的Worker，告诉Worker已经完成注册，随之进程步骤3，即Worker定期发送心跳信息给Master；如果注册失败，则会发送RegisterWorkerFailed消息，Worker打印出错误日志并结束worker启动。
d） 在Master中，Master接收到Worker注册信息后，先判断Master当前状态是处于standby状态，如果是则忽略该消息，如果在注册列表中发现了该worker的编号，则发送注册失败的消息。判断完毕后，使用registerWorker方法把该Worker加入到列表中，用户集群进行处理任务时进行调度。Master.receiveAndReply方法中注册Worer代码：
此处Master会处理workerid, workerhost, workerPort, workRef终端点引用，worker的cores, memory,worker的workerWebUiUrl地址
里面的逻辑大概是首先判断Master是不是standBy,是的话返回MasterInStandby，在检查idToWorker是否注册过该Worker，不能重复注册。如果以上两种情况均未发生，则会去注册worker， 创建WorkerInfo封住该Worker的具体信息，然后调用registerWorker(worker)方法：
case RegisterWorker(
id, workerHost, workerPort, workerRef, cores, memory, workerWebUiUrl, masterAddress) =>
logInfo("Registering worker %s:%d with %d cores, %s RAM".format(
workerHost, workerPort, cores, Utils.megabytesToString(memory)))
if (state == RecoveryState.STANDBY) {
workerRef.send(MasterInStandby)
} else if (idToWorker.contains(id)) {
workerRef.send(RegisterWorkerFailed("Duplicate worker ID")) //已经存在
} else {
val worker = new WorkerInfo(id, workerHost, workerPort, cores, memory,
workerRef, workerWebUiUrl)
if (registerWorker(worker)) {
persistenceEngine.addWorker(worker) //注册worker
workerRef.send(RegisteredWorker(self, masterWebUiUrl, masterAddress))
schedule()
} else {
val workerAddress = worker.endpoint.address
logWarning("Worker registration failed. Attempted to re-register worker at same " +
"address: " + workerAddress)
workerRef.send(RegisterWorkerFailed("Attempted to re-register worker at same address: "
+ workerAddress))
}
}
此处Master会处理workerid, workerhost, workerPort, workRef终端点引用，worker的cores, memory,worker的workerWebUiUrl地址
里面的逻辑大概是首先判断Master是不是standBy,是的话返回MasterInStandby，在检查idToWorker是否注册过该Worker，不能重复注册。如果以上两种情况均未发生，则会去注册worker， 创建WorkerInfo封住该Worker的具体信息，然后调用registerWorker(worker)方法：
private def registerWorker(worker: WorkerInfo): Boolean = {
// There may be one or more refs to dead workers on this same node (w/ different ID's),
// remove them.
workers.filter { w =>
(w.host == worker.host && w.port == worker.port) && (w.state == WorkerState.DEAD)
}.foreach { w =>
workers -= w
}
val workerAddress = worker.endpoint.address
if (addressToWorker.contains(workerAddress)) {
val oldWorker = addressToWorker(workerAddress)
if (oldWorker.state == WorkerState.UNKNOWN) {
// A worker registering from UNKNOWN implies that the worker was restarted during recovery.
// The old worker must thus be dead, so we will remove it and accept the new worker.
removeWorker(oldWorker)
} else {
logInfo("Attempted to re-register worker at same address: " + workerAddress)
return false
}
}
workers += worker
idToWorker(worker.id) = worker
addressToWorker(workerAddress) = worker
true
}
.onComplete {
// This is a very fast action so we can use "ThreadUtils.sameThread"
case Success(msg) =>
Utils.tryLogNonFatalError {
handleRegisterResponse(msg)
}
case Failure(e) =>
logError(s"Cannot register with master: ${masterEndpoint.address}", e)
System.exit(1)
e) 当worker接收到注册成功后，会定时发送heartbeat给Master，以便Master了解Worker的实时状态。间隔时间可以设置。
Worker收到注册成功后会先设置registered = true表明注册成功，然后更新Master信息， 记录此Worker现在注册给哪个Master，之后就会启动定时任务发送心跳， 同时Worker还会向Master汇报Worker中Executor的最新状态如每个Executor的对应处理的appid, executor本身id，executer使用的cores， executor的状态以及Driver的信息.
val execs = executors.values.map { e =>
new ExecutorDescription(e.appId, e.execId, e.cores, e.state)
}
masterRef.send(WorkerLatestState(workerId, execs.toList, drivers.keys.toSeq))
private val HEARTBEAT_MILLIS = conf.getLong("spark.worker.timeout", 60) * 1000 / 4
当 Worker获取到注册成功消息后，先记录日志并更新Master信息，然后启动定时调度进程发送心跳信息，该调度进程时间间隔为上面所所定义的HEARTBEAT_MILLIS 值。
Master在收到Worker注册请求，返回注册成功之后还会执行一步骤：
schedule()
/**
* Schedule the currently available resources among waiting apps. This method will be called
* every time a new app joins or resource availability changes.
*/
private def schedule(): Unit = {
if (state != RecoveryState.ALIVE) {
return
}
// Drivers take strict precedence over executors
val shuffledAliveWorkers = Random.shuffle(workers.toSeq.filter(_.state == WorkerState.ALIVE))
val numWorkersAlive = shuffledAliveWorkers.size
var curPos = 0
for (driver <- waitingDrivers.toList) { // iterate over a copy of waitingDrivers
// We assign workers to each waiting driver in a round-robin fashion. For each driver, we
// start from the last worker that was assigned a driver, and continue onwards until we have
// explored all alive workers.
var launched = false
var numWorkersVisited = 0
while (numWorkersVisited < numWorkersAlive && !launched) {
val worker = shuffledAliveWorkers(curPos)
numWorkersVisited += 1
if (worker.memoryFree >= driver.desc.mem && worker.coresFree >= driver.desc.cores) {
launchDriver(worker, driver)
waitingDrivers -= driver
launched = true
}
curPos = (curPos + 1) % numWorkersAlive
}
}
startExecutorsOnWorkers()
}
意思是当新加入了Worker节点，获取所有可用的Alive的Worker， 查看是否有waiting的App没有分到资源的， 有的话遍历这个waitingDrivers(对应wainting状态的APP)， 根据内存和核数是否满足if (worker.memoryFree >= driver.desc.mem && worker.coresFree >= driver.desc.cores) 来判断是否launch driver， 然后就调用startExecutorsOnWorkers()来启动Worker的Executors
Spark运行时通信
driver提交程序时，sc会向Master发送注册应用消息。Master会为之注册Executor，Executor发送注册成功消息，当RDD出发computing时，DAGScheduler进行划分Stage，并将Stage转化为Taskset，接着由TaskScheduler向注册的Executor发送执行消息，Executor接受到消息后启动运行。最后当所有任务运行时，由Driver处理结果并回收资源。如图：
运行时通信.png
1）执行程序main方法，启动SparkContext，在初始化时，先实例化StandaloneScheduleBackend对象继承CoarseGrainedSchedulerBackend会先实例化父类，在实例化该对象时候start过程继承DriverEndpoint和创建AppClient的ClientEndpoint实际上是两个终端点，然后再初始化TaskSchedulerImpl，调用backend.start
CoarseGrainedSchedulerBackend的start方法：
override def start() {
val properties = new ArrayBuffer[(String, String)]
for ((key, value) <- scheduler.sc.conf.getAll) {
if (key.startsWith("spark.")) {
properties += ((key, value))
}
}
// TODO (prashant) send conf instead of properties
driverEndpoint = createDriverEndpointRef(properties)
}
protected def createDriverEndpointRef(
properties: ArrayBuffer[(String, String)]): RpcEndpointRef = {
rpcEnv.setupEndpoint(ENDPOINT_NAME, createDriverEndpoint(properties))
}
protected def createDriverEndpoint(properties: Seq[(String, String)]): DriverEndpoint = {
new DriverEndpoint(rpcEnv, properties)
}
创建了StandaloneAppClient
(2)在StandaloneAppClient通过tryResisterAllMasters来实现Application向Master的注册
(3)当Master收到注册请求之后进行处理， 注册完毕之后会发送注册成功消息给StandaloneApplClient, 然后调用startExecutorsOnWorkers方法运行应用。
(4)Executor注册过程
a)调用startExecutorsOnWorkers会分配资源来运行应用程序， 调用allcateWorkerResourceToExecutors实现在Worker中启动Executor，allcateWorkerResourceToExecutors里面有个lanchExecutor方法，这里面会调用send(LaunchTask)给Worker， Worker收到后会实例化ExecutorRunner对象，在ExecutorRunner创建进程生成器ProcessBuilder，然后此生成器根据ApplicationInfo中的command创建CoarseGrainedExecutorBackend对象，也就是Executor运行的容器， 最后Worker向Master发送ExecutorStateChanged通知Executor容器创建完毕，
b)进程生成器创建CoarseGrainedExecutorBackend对象时，调用了start方法，其半生对象会注册Executor终端点，会触发onStart方法，会发送注册Executor消息RegisterExecutor到Driverpoint,如果注册成功Driverpoint会返回RegisteredExecutor消息给ExecutorEndppoint。当ExecutorEndppoint实际上是CoarseGrainedExecutorBackend收到注册成功， 则会创建Executor对象。
c)DriverEndpoint会创建一个守护线程，监听是否有taskSets过来
private val reviveThread =
ThreadUtils.newDaemonSingleThreadScheduledExecutor("driver-revive-thread")
override def onStart() {
// Periodically revive offers to allow delay scheduling to work
val reviveIntervalMs = conf.getTimeAsMs("spark.scheduler.revive.interval", "1s")
reviveThread.scheduleAtFixedRate(new Runnable {
override def run(): Unit = Utils.tryLogNonFatalError {
Option(self).foreach(_.send(ReviveOffers))
}
}, 0, reviveIntervalMs, TimeUnit.MILLISECONDS)
}
调用makeoffers
// Make fake resource offers on all executors
private def makeOffers() {
// Filter out executors under killing
val activeExecutors = executorDataMap.filterKeys(executorIsAlive)
val workOffers = activeExecutors.map { case (id, executorData) =>
new WorkerOffer(id, executorData.executorHost, executorData.freeCores)
}.toSeq
launchTasks(scheduler.resourceOffers(workOffers))
}
executorData.executorEndpoint.send(LaunchTask(new SerializableBuffer(serializedTask)))
def launchTask(
context: ExecutorBackend,
taskId: Long,
attemptNumber: Int,
taskName: String,
serializedTask: ByteBuffer): Unit = {
val tr = new TaskRunner(context, taskId = taskId, attemptNumber = attemptNumber, taskName,
serializedTask)
runningTasks.put(taskId, tr)
threadPool.execute(tr)
}
TaskRunner的run方法体内就会执行Task， 当执行完毕时会向Driver汇报此Task在Executor上执行完毕了。
execBackend.statusUpdate(taskId, TaskState.FINISHED, serializedResult)
------------------------------------------------------------------------------------
override def statusUpdate(taskId: Long, state: TaskState, data: ByteBuffer) {
val msg = StatusUpdate(executorId, taskId, state, data)
driver match {
case Some(driverRef) => driverRef.send(msg)
case None => logWarning(s"Drop $msg because has not yet connected to driver")
}
}
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