1.概述

  JobManager 是 Flink 集群的主节点，它包含三大重要的组件：

• ResourceManager
  • Flink集群的资源管理器，负责slot的管理和申请工作。
• Dispatcher
  • 负责接收客户端提交的 JobGraph，随后启动一个Jobmanager，类似 Yarn中的ApplicationMaster角色，类似Spark中的Driver角色。
• JobManager
  • 负责一个具体job的执行，在Flink集群中，可能会有多个JobManager 同时执行，job的主控层序
• WebmonitorEndpoint
  • 该类型中维护了很多的Handler，如果客户端通过flink run 的方式提交flink提交一个job到flink集群，最后都是由WebmonitorEndpoint来接收，并决定使用哪个handler进行处理。

  总而言之：Flink集群的主节点内部运行着 ResourceManager 和 Dispatcher 对象，当客户端提交一个job到Flink集群运行时(客户端会将job先构建为JobGraph对象)，Dsipatcher 负责启动Jobmanager对象，该对象负责该job内部的Task执行以及向ResourceManager申请运行该Task所需要的资源。

2.JobManager启动

2.1 StandaloneSessionClusterEntrypoint(解析+启动)

根据Flink主节点启动脚本分析可知，JobManager的启动主类为：StandAloneSessionClusterEntrypoint。Flink集群主节点启动做了两件事情：解析参数以及配置文件，启动相关的服务。

/*
 *  注释： flink有三种方式执行应用程序：session mode, per-job mode, applocation mode
 *  模型的区别主要包含：
 *  1. 集群生命周期和资源隔离保证
 *  2. 应用程序的main()方法是在客户端执行还是在集群执行
 */
/**
 * Entry point for the standalone session cluster.
 */
public class StandaloneSessionClusterEntrypoint extends SessionClusterEntrypoint {
	public StandaloneSessionClusterEntrypoint(Configuration configuration) {
		super(configuration);
	}

	@Override
	protected DefaultDispatcherResourceManagerComponentFactory createDispatcherResourceManagerComponentFactory(Configuration configuration) {
		/*************************************************
		 *  注释：
		 *  1、参数是：StandaloneResourceManagerFactory 实例
		 *  2、返回值：DefaultDispatcherResourceManagerComponentFactory 实例
		 */
		return DefaultDispatcherResourceManagerComponentFactory
			.createSessionComponentFactory(StandaloneResourceManagerFactory.getInstance());
	}

	/*************************************************
	 * 
	 *  注释： 入口
	 */
	public static void main(String[] args) {

		// 注释：提供对 JVM 执行环境的访问的实用程序类，如执行用户(getHadoopUser())、启动选项或JVM版本。
		// startup checks and logging
		EnvironmentInformation.logEnvironmentInfo(LOG, StandaloneSessionClusterEntrypoint.class.getSimpleName(), args);

		// 注释：注册信号处理
		SignalHandler.register(LOG);

		// 注释： 安装安全关闭的钩子(保证Flink集群关闭或者宕机后关闭对应的服务)
		// 注释： Flink集群启动过程中或者在启动好了之后的运行中，都有可能接收到关闭集群的命令
		JvmShutdownSafeguard.installAsShutdownHook(LOG);

		EntrypointClusterConfiguration entrypointClusterConfiguration = null;
		final CommandLineParser<EntrypointClusterConfiguration> commandLineParser = new CommandLineParser<>(
			new EntrypointClusterConfigurationParserFactory());
		try {
			/*************************************************
			 *  注释： 解析传入的参数
			 *  内部通过 EntrypointClusterConfigurationParserFactory 解析配置文件，
			 *  返回 EntrypointClusterConfiguration 为 ClusterConfiguration 的子类
			 */
			entrypointClusterConfiguration = commandLineParser.parse(args);
		} catch(FlinkParseException e) {
			LOG.error("Could not parse command line arguments {}.", args, e);		commandLineParser.printHelp(StandaloneSessionClusterEntrypoint.class.getSimpleName());
			System.exit(1);
		}
		/*************************************************
		 *  注释：解析 flink 的配置文件： fink-conf.ymal
		 */
		Configuration configuration = loadConfiguration(entrypointClusterConfiguration);

		/*************************************************
		 *  注释：创建 StandaloneSessionClusterEntrypoint对象
		 */
		StandaloneSessionClusterEntrypoint entrypoint = new StandaloneSessionClusterEntrypoint(configuration);

		/*************************************************
		 *  注释：启动集群的entrypoint
		 * 方法接收的是父类 ClusterEntrypoint，可想而知：其他几种启动方式也通过该方法。
		 */
		ClusterEntrypoint.runClusterEntrypoint(entrypoint);
	}
}

2.2 ClusterEntrypoint.runClusterEntrypoint(启动主节点)

public static void runClusterEntrypoint(ClusterEntrypoint clusterEntrypoint) {

		final String clusterEntrypointName = clusterEntrypoint.getClass().getSimpleName();
		try {

			/*************************************************
			 *  注释： 启动 Flink 主节点： JobManager
			 */
			clusterEntrypoint.startCluster();

		} catch(ClusterEntrypointException e) {
			LOG.error(String.format("Could not start cluster entrypoint %s.", clusterEntrypointName), e);
			System.exit(STARTUP_FAILURE_RETURN_CODE);
		}

		/*************************************************
		 *  注释： 获取结果(启动完成)
		 */
		clusterEntrypoint.getTerminationFuture().whenComplete((applicationStatus, throwable) -> {
			final int returnCode;

			if(throwable != null) {
				returnCode = RUNTIME_FAILURE_RETURN_CODE;
			} else {
				returnCode = applicationStatus.processExitCode();
			}

			LOG.info("Terminating cluster entrypoint process {} with exit code {}.", clusterEntrypointName, returnCode, throwable);
			System.exit(returnCode);
		});
	}

2.3 clusterEntrypoint.startCluster(启动主节点detail)

• 1.注册了一些插件，使用单独的类加载器加载
• 2.根据配置信息初始化了文件系统

public void startCluster() throws ClusterEntrypointException {
		LOG.info("Starting {}.", getClass().getSimpleName());

		try {
			replaceGracefulExitWithHaltIfConfigured(configuration);
			/*************************************************
			 *  注释： PluginManager 是新版支持提供通用的插件机制
			 *  负责管理集群插件，这些插件是使用单独的类加载器加载的，以便它们的依赖关系，不要干扰 Flink 的依赖关系。
			 */
			PluginManager pluginManager = PluginUtils.createPluginManagerFromRootFolder(configuration);
			/*************************************************
			 *  注释： 根据配置初始化文件系统
			 *  三种东西；
			 *  1、本地   Local  客户端的时候会用  JobGragh ===> JobGraghFile
			 *  2、HDFS	 FileSytem(DistributedFileSystem)
			 *  3、封装对象	HadoopFileSystem， 里面包装了 HDFS 的 FileSYSTEM 实例对象
			 */
			configureFileSystems(configuration, pluginManager);
			//注释：配置安全相关配置：securityContext = NoOpSecurityContext
			SecurityContext securityContext = installSecurityContext(configuration);

			/*************************************************
			 *  注释： 通过一个线程来运行
			 */
			securityContext.runSecured((Callable<Void>) () -> {
				/*************************************************
				 *  注释： 集群启动入口
				 */
				runCluster(configuration, pluginManager);
				return null;
			});
		} catch(Throwable t) {
			final Throwable strippedThrowable = ExceptionUtils.stripException(t, UndeclaredThrowableException.class);

			try {
				// clean up any partial state
				shutDownAsync(ApplicationStatus.FAILED, ExceptionUtils.stringifyException(strippedThrowable), false)
					.get(INITIALIZATION_SHUTDOWN_TIMEOUT.toMilliseconds(), TimeUnit.MILLISECONDS);
			} catch(InterruptedException | ExecutionException | TimeoutException e) {
				strippedThrowable.addSuppressed(e);
			}
			throw new ClusterEntrypointException(String.format("Failed to initialize the cluster entrypoint %s.", getClass().getSimpleName()),
				strippedThrowable);
		}
	}

2.4 runCluster(初始化+实例化)

通过runCluster(configuration, pluginManager)方法启动集群，在该方法中做了两件事情：

• initializeServices() 初始化相关服务(RpcService/haServices/blobServer/heartbeatServices/metricRegistry/archivedExecutionGraphStore)
• dispatcherResourceManagerComponentFactory.create() 启动 Dispatcher 和 ResourceManager 服务。
• dispatcherResourceManagerComponentFactory内部有三个成员变量：dispatcherRunnerFactory、resourceManagerFactory、restEndpointFactory

private void runCluster(Configuration configuration, PluginManager pluginManager) throws Exception {
		synchronized(lock) {

/***  注释： 初始化服务，如 JobManager 的 Akka RPC 服务，HA 服务，心跳检查服务等 Master 节点需要使用到的服务
* 1、commonRpcService: 基于 Akka 的 RpcService 实现。RPC 服务启动 Akka 参与者来接收从 RpcGateway 调用 RPC
* 2、haServices: 提供对高可用性所需的所有服务的访问注册，分布式计数器和领导人选举
* 3、blobServer: 负责监听传入的请求生成线程来处理这些请求。还负责创建要存储的目录结构blob 或临时缓存它们。
* 4、heartbeatServices:提供心跳所需的所有服务。包括创建心跳接收器和心跳发送者。
* 5、metricRegistry: 跟踪所有已注册的 Metric，它作为连接 MetricGroup 和 MetricReporter
* 6、archivedExecutionGraphStore: 存储执行图ExecutionGraph的可序列化形式。
			 */
			initializeServices(configuration, pluginManager);

			// 注释： 将 jobmanager 地址写入配置
			// write host information into configuration
			configuration.setString(JobManagerOptions.ADDRESS, commonRpcService.getAddress());
			configuration.setInteger(JobManagerOptions.PORT, commonRpcService.getPort());

/*************************************************
*  注释： 初始化一个 DefaultDispatcherResourceManagerComponentFactory 工厂实例
*  内部初始化了四大工厂实例
*  1、DispatcherRunnerFactory = DefaultDispatcherRunnerFactory
*  2、ResourceManagerFactory = StandaloneResourceManagerFactory
*  3、RestEndpointFactory（WebMonitorEndpoint的工厂） = SessionRestEndpointFactory
*  返回值：DefaultDispatcherResourceManagerComponentFactory
*  内部包含了这三个工厂实例，即三个成员变量
*  再补充一个：dispatcherLeaderProcessFactoryFactory = SessionDispatcherLeaderProcessFactoryFactory
			 */
			final DispatcherResourceManagerComponentFactory dispatcherResourceManagerComponentFactory =
				createDispatcherResourceManagerComponentFactory(configuration);

/*************************************************
*   注释：启动关键组件：Dispatcher 和 ResourceManager。
*  1、Dispatcher: 负责接收客户端提交的作业，持久化它们，生成要执行的作业管理器任务，并在主任务失败时恢复它们。此外, 它知道关于 Flink 会话集群的状态。负责为新提交的作业启动新的 JobManager服务
*  2、ResourceManager: 负责资源的调度。在整个 Flink 集群中只有一个 ResourceManager，资源相关的内容都由这个服务负责	registerJobManager(JobMasterId, ResourceID, String, JobID, Time) 负责注册 jobmaster,requestSlot(JobMasterId, SlotRequest, Time) 从资源管理器请求一个槽
 *  3、WebMonitorEndpoint: 服务于 web 前端 Rest 调用的 Rest 端点，用于接收客户端发送的执行任务的请求
 */
			clusterComponent = dispatcherResourceManagerComponentFactory
				.create(configuration, 
                        ioExecutor, 
                        commonRpcService, 
                        haServices,
					  blobServer, 
                        heartbeatServices, 
                        metricRegistry,
					 archivedExecutionGraphStore,
					new RpcMetricQueryServiceRetriever(metricRegistry.getMetricQueryServiceRpcService()),
					this);

			/*************************************************
			 *  注释：集群关闭时的回调
			 */
			clusterComponent.getShutDownFuture().whenComplete((ApplicationStatus applicationStatus, Throwable throwable) -> {
				if(throwable != null) {
					shutDownAsync(ApplicationStatus.UNKNOWN, ExceptionUtils.stringifyException(throwable), false);
				} else {
					// This is the general shutdown path. If a separate more specific shutdown was
					// already triggered, this will do nothing
					shutDownAsync(applicationStatus, null, true);
				}
			});
		}
	}

2.5 initializeServices(实例化detail)

该方法是初始化各种服务，有以下服务：

• commonRpcService：
  • 该组件启动后，其内部启动一个ActorSystem，当前ActorSystem内部启动一个Actor。
  • 该组件是一个基于Akka的ActorSystem，其实就是一个tcp的rpc服务。
• ioExecutor
  • 初始化一个专门负责IO的线程池，数量=4*cpu个数。
• haServices
  • HA service 相关的实现，根据用户需求配置不同的HA服务，例如：ZooKeeperHaServices。
• blobServer
  • 负责一些大文件的上传，比如用户作业的 jar 包、TM 上传 log 文件等。
• heartbeatServices
  • 初始化一个心跳服务，管理主节点上组件的心跳服务。(本质是heartbeatServices对象)
• metricRegistry
  • 初始化一个性能监控服务
• archivedExecutionGraphStore
  • 初始化一个存储ExecutionGraph的服务

protected void initializeServices(Configuration configuration, PluginManager pluginManager) throws Exception {

        LOG.info("Initializing cluster services.");

        synchronized(lock) {

            /*************************************************
             *  创建 Akka rpc 服务 commonRpcService： 基于 Akka 的 RpcService 实现。
             *  RPC 服务启动 Akka 参与者来接收从 RpcGateway 调用 RPC
             *  commonRpcService是一个基于 akka 的 actorSystem，其实就是一个 tcp 的 rpc 服务，端口为：6123
             *  1、初始化 ActorSystem
             *  2、启动 Actor
             */
            commonRpcService = AkkaRpcServiceUtils
                .createRemoteRpcService(configuration, configuration.getString(JobManagerOptions.ADDRESS), getRPCPortRange(configuration),
                    configuration.getString(JobManagerOptions.BIND_HOST), configuration.getOptional(JobManagerOptions.RPC_BIND_PORT));

            // TODO_MA 注释： 设置 host 和 port
            // update the configuration used to create the high availability services
            configuration.setString(JobManagerOptions.ADDRESS, commonRpcService.getAddress());
            configuration.setInteger(JobManagerOptions.PORT, commonRpcService.getPort());

            /*************************************************
             *  初始化一个 ioExecutor
             *  如果当前节点有32 个 cpu ,那么当前 ioExecutor启动的线程的数量为：128
             */
            ioExecutor = Executors.newFixedThreadPool(ClusterEntrypointUtils.getPoolSize(configuration), new ExecutorThreadFactory("cluster-io"));

            /*************************************************
             *  HA service 相关的实现，它的作用有很多，到底使用哪种根据用户的需求来定义
             *  比如：处理 ResourceManager 的 leader 选举、JobManager leader 的选举等；
             *  haServices = ZooKeeperHaServices
             */
            haServices = createHaServices(configuration, ioExecutor);

            /*************************************************
             *  注释： 第四步： 初始化一个 BlobServer
             *  主要管理一些大文件的上传等，比如用户作业的 jar 包、TM 上传 log 文件等
             *  Blob 是指二进制大对象也就是英文 Binary Large Object 的缩写
             */
            blobServer = new BlobServer(configuration, haServices.createBlobStore());
            blobServer.start();

            /*************************************************
             *  初始化一个心跳服务
             *  在主节点中很多角色都有心跳服务。这些角色的心跳服务，都是在这heartbeatServices 的基础之上创建的。谁需要心跳服务，通过 heartbeatServices 去提供一个实例 HeartBeatImpl，用来完成心跳
             */
            heartbeatServices = createHeartbeatServices(configuration);

            /*************************************************
             *  1、metricQueryServiceRpcService 也是一个 ActorySystem
             *  2、用来跟踪所有已注册的Metric
             */
            metricRegistry = createMetricRegistry(configuration, pluginManager);
            final RpcService metricQueryServiceRpcService = MetricUtils.startRemoteMetricsRpcService(configuration, commonRpcService.getAddress());
            metricRegistry.startQueryService(metricQueryServiceRpcService, null);
            final String hostname = RpcUtils.getHostname(commonRpcService);
            processMetricGroup = MetricUtils
                .instantiateProcessMetricGroup(metricRegistry, hostname, ConfigurationUtils.getSystemResourceMetricsProbingInterval(configuration));

 /*************************************************
*  ArchivedExecutionGraphStore: 存储execution graph的服务， 默认有两种实现，
*  1、MemoryArchivedExecutionGraphStore 主要是在内存中缓存，
*  2、FileArchivedExecutionGraphStore 会持久化到文件系统，也会在内存中缓存。
 *  这些服务都会在前面第二步创建 DispatcherResourceManagerComponent 对象时使用到。
*  默认实现是基于 File 的
*/
            archivedExecutionGraphStore = createSerializableExecutionGraphStore(configuration, commonRpcService.getScheduledExecutor());
        }
    }

2.6 webMonitorEndpoint 启动

webMonitorEndpoint 启动分为两部分：

• webMonitorEndpoint 的实例化
  • 通过restEndpointFactory.createRestEndpoint()方法创建webMonitorEndpoint对象
  • 初始化各种Handler对象，包括JobSubmitHandler
  • 启动Netty服务端
  • 启动完成之后，会进行选举，选举成功后会执行leaderElectionService.isLeader() ==> leaderContender.grantLeaderShip()

该方法通过dispatcherResourceManagerComponentFactory中的三个工厂对象创建对应的三个实例对象。

• webMonitorEndpoint = restEndpointFactory.createRestEndpoint()
• resourceManager = resourceManagerFactory.createResourceManager()
• dispatcherRunner = dispatcherRunnerFactory.createDispatcherRunner()

@Override
	public DispatcherResourceManagerComponent  create(Configuration configuration, Executor ioExecutor, RpcService rpcService,
		HighAvailabilityServices highAvailabilityServices, BlobServer blobServer, HeartbeatServices heartbeatServices, MetricRegistry metricRegistry,
		ArchivedExecutionGraphStore archivedExecutionGraphStore, MetricQueryServiceRetriever metricQueryServiceRetriever,
		FatalErrorHandler fatalErrorHandler) throws Exception {
		// 注释： 检索当前leader并进行通知一个倾听者的服务
		LeaderRetrievalService dispatcherLeaderRetrievalService = null;
		//注释： 检索当前leader并进行通知一个倾听者的服务
		LeaderRetrievalService resourceManagerRetrievalService = null;
		// 注释： 服务于web前端Rest调用的Rest端点
		WebMonitorEndpoint<?> webMonitorEndpoint = null;
		// 注释： ResourceManager实现。资源管理器负责资源的分配和记帐
		ResourceManager<?> resourceManagr = null;
		//注释： 封装Dispatcher如何执行的
		DispatcherRunner dispatcherRunner = null;
		try {
			// 注释： 用于 Dispatcher leader 选举
			//注释： dispatcherLeaderRetrievalService = ZooKeeperLeaderRetrievalService
			dispatcherLeaderRetrievalService = highAvailabilityServices.getDispatcherLeaderRetriever();
			// 注释： 用于 ResourceManager leader 选举
			// 注释： resourceManagerRetrievalService = ZooKeeperLeaderRetrievalService
			resourceManagerRetrievalService = highAvailabilityServices.getResourceManagerLeaderRetriever();
			// 注释： Dispatcher 的 Gateway
			final LeaderGatewayRetriever<DispatcherGateway> dispatcherGatewayRetriever = new RpcGatewayRetriever<>(rpcService,
				DispatcherGateway.class, DispatcherId::fromUuid, 10, Time.milliseconds(50L));
			// 注释： ResourceManager 的 Gateway
			final LeaderGatewayRetriever<ResourceManagerGateway> resourceManagerGatewayRetriever = new RpcGatewayRetriever<>(rpcService,
				ResourceManagerGateway.class, ResourceManagerId::fromUuid, 10, Time.milliseconds(50L));

			//注释： 创建线程池，用于执行 WebMonitorEndpoint 所接收到的 client 发送过来的请求
			final ScheduledExecutorService executor = WebMonitorEndpoint
	.createExecutorService(configuration.getInteger(RestOptions.SERVER_NUM_THREADS),
					configuration.getInteger(RestOptions.SERVER_THREAD_PRIORITY), "DispatcherRestEndpoint");
			//注释 初始化 MetricFetcher
			final long updateInterval = configuration.getLong(MetricOptions.METRIC_FETCHER_UPDATE_INTERVAL);
			final MetricFetcher metricFetcher = updateInterval == 0 ? VoidMetricFetcher.INSTANCE : MetricFetcherImpl
				.fromConfiguration(configuration, metricQueryServiceRetriever, dispatcherGatewayRetriever, executor);
/*************************************************
 *  注释： 创建 WebMonitorEndpoint 实例， 在 Standalone模式下：DispatcherRestEndpoint
 *  1、restEndpointFactory = SessionRestEndpointFactory
*  2、webMonitorEndpoint = DispatcherRestEndpoint
 *  3、highAvailabilityServices.getClusterRestEndpointLeaderElectionService() = ZooKeeperLeaderElectionService
			 */
			webMonitorEndpoint = restEndpointFactory
				.createRestEndpoint(configuration, dispatcherGatewayRetriever, resourceManagerGatewayRetriever, blobServer, executor, metricFetcher,
					highAvailabilityServices.getClusterRestEndpointLeaderElectionService(), fatalErrorHandler);
			/*************************************************
			 *  注释： 启动 DispatcherRestEndpoint
			 *  1、启动 Netty 服务端
			 *  2、选举
			 *  3、启动定时任务 ExecutionGraphCacheCleanupTask
			 */
			log.debug("Starting Dispatcher REST endpoint.");
			webMonitorEndpoint.start();

			final String hostname = RpcUtils.getHostname(rpcService);

			/*************************************************
			 *  注释： 创建 StandaloneResourceManager 实例对象
			 *  1、resourceManager = StandaloneResourceManager
			 *  2、resourceManagerFactory = StandaloneResourceManagerFactory
			 */
			resourceManager = resourceManagerFactory
				.createResourceManager(configuration, ResourceID.generate(), rpcService, highAvailabilityServices, heartbeatServices,
					fatalErrorHandler, new ClusterInformation(hostname, blobServer.getPort()), webMonitorEndpoint.getRestBaseUrl(), metricRegistry,
					hostname);

			final HistoryServerArchivist historyServerArchivist = HistoryServerArchivist
				.createHistoryServerArchivist(configuration, webMonitorEndpoint, ioExecutor);

			final PartialDispatcherServices partialDispatcherServices = new PartialDispatcherServices(configuration, highAvailabilityServices,
				resourceManagerGatewayRetriever, blobServer, heartbeatServices,
				() -> MetricUtils.instantiateJobManagerMetricGroup(metricRegistry, hostname), archivedExecutionGraphStore, fatalErrorHandler,
				historyServerArchivist, metricRegistry.getMetricQueryServiceGatewayRpcAddress());
			/*************************************************
			 *  注释： 创建 并启动 Dispatcher
			 *  1、dispatcherRunner = DispatcherRunnerLeaderElectionLifecycleManager
			 *  2、dispatcherRunnerFactory = DefaultDispatcherRunnerFactory
			 *  第一个参数： ZooKeeperLeaderElectionService
			 *  -
			 *  老版本： 这个地方是直接创建一个 Dispatcher 对象然后调用 dispatcher.start() 来启动
			 *  新版本： 直接创建一个 DispatcherRunner， 内部就是要创建和启动 Dispatcher
			 */
			log.debug("Starting Dispatcher.");
			dispatcherRunner = dispatcherRunnerFactory
.createDispatcherRunner(highAvailabilityServices.getDispatcherLeaderElectionService(), fatalErrorHandler,
					//  注释： 注意第三个参数
					new HaServicesJobGraphStoreFactory(highAvailabilityServices), ioExecutor, rpcService, partialDispatcherServices);

			/*************************************************
			 *  注释： resourceManager 启动
			 */
			log.debug("Starting ResourceManager.");
			resourceManager.start();
			/*************************************************
			 *  注释： resourceManagerRetrievalService 启动
			 */
			resourceManagerRetrievalService.start(resourceManagerGatewayRetriever);
			/*************************************************
			 *  注释： ZooKeeperHaServices 启动
			 */
			dispatcherLeaderRetrievalService.start(dispatcherGatewayRetriever);
			/*************************************************
			 *  注释： 构建 DispatcherResourceManagerComponent
			 */
			return new DispatcherResourceManagerComponent(dispatcherRunner, resourceManager, dispatcherLeaderRetrievalService,
				resourceManagerRetrievalService, webMonitorEndpoint);
		} catch(Exception exception) {
			................
	}

2.6.1 restEndpointFactory.createRestEndpoint(实例化)

restEndpointFactory = SessionRestEndpointFactory(代码跳转的类)，创建webMonitorEndpoint实例化对象，返回的是DispatcherRestEndpoint对象。webMonitorEndpoint处理客户端所有的请求。

public enum SessionRestEndpointFactory implements RestEndpointFactory<DispatcherGateway> {
	INSTANCE;

	@Override
	public WebMonitorEndpoint<DispatcherGateway> createRestEndpoint(Configuration configuration,
		LeaderGatewayRetriever<DispatcherGateway> dispatcherGatewayRetriever,
		LeaderGatewayRetriever<ResourceManagerGateway> resourceManagerGatewayRetriever, TransientBlobService transientBlobService,
		ScheduledExecutorService executor, MetricFetcher metricFetcher, LeaderElectionService leaderElectionService,
		FatalErrorHandler fatalErrorHandler) throws Exception {

		// TODO_MA 注释：
		final RestHandlerConfiguration restHandlerConfiguration = RestHandlerConfiguration.fromConfiguration(configuration);

		/*************************************************
		 * RestEndpointFactory.createExecutionGraphCache(restHandlerConfiguration) = DefaultExecutionGraphCache
		 */
		return new DispatcherRestEndpoint(RestServerEndpointConfiguration.fromConfiguration(configuration), dispatcherGatewayRetriever, configuration,
			restHandlerConfiguration, resourceManagerGatewayRetriever, transientBlobService, executor, metricFetcher, leaderElectionService,
		RestEndpointFactory.createExecutionGraphCache(restHandlerConfiguration), fatalErrorHandler);
	}
}

2.6.2 webMonitorEndpoint.start(启动)

该方法主要作用：

• 初始化各种Handler，包括： JobSubmitHandler(专门处理客户端提交的作业)
  • 客户端提交的job时，由Jobmanager中的Netty服务端的JobSubmitHandler来处理
  • JobSubmitHandler接收到客户端的请求，通过handleRequest方法做了以下事情：
    • 恢复得到 JobGragh
    • 获取jar包以及依赖jar包
    • 上传JobGraph + 程序jar + 依赖 jar，然后提交任务(Dispatcher.submitJob)
• 启动 Netty 服务端(启动位置：WebMonitorEndpoint)

public final void start() throws Exception {
		synchronized(lock) {
			Preconditions.checkState(state == State.CREATED, "The RestServerEndpoint cannot be restarted.");
			log.info("Starting rest endpoint.");
			final Router router = new Router();
			final CompletableFuture<String> restAddressFuture = new CompletableFuture<>();

			/*************************************************
			 *  注释： 主要是初始化各种 Handler，包括： JobSubmitHandler
			 */
			handlers = initializeHandlers(restAddressFuture);

			//  注释： 针对所有的 Handlers 进行排序，排序规则：RestHandlerUrlComparator
			/* sort the handlers such that they are ordered the following:
			 * /jobs
			 * /jobs/overview
			 * /jobs/:jobid
			 * /jobs/:jobid/config
			 * /:*
			 */
			Collections.sort(handlers, RestHandlerUrlComparator.INSTANCE);

			checkAllEndpointsAndHandlersAreUnique(handlers);
			handlers.forEach(handler -> registerHandler(router, handler, log));

			/*************************************************
			 *  注释： 启动 Netty 服务端
			 */
			ChannelInitializer<SocketChannel> initializer = new ChannelInitializer<SocketChannel>() {
				@Override
				protected void initChannel(SocketChannel ch) {
					RouterHandler handler = new RouterHandler(router, responseHeaders);
					// SSL should be the first handler in the pipeline
					if(isHttpsEnabled()) {
						ch.pipeline().addLast("ssl", new RedirectingSslHandler(restAddress, restAddressFuture, sslHandlerFactory));
					}
					ch.pipeline()
						.addLast(new HttpServerCodec())
						.addLast(new FileUploadHandler(uploadDir))
						.addLast(new FlinkHttpObjectAggregator(maxContentLength, responseHeaders))
						.addLast(new ChunkedWriteHandler())
						.addLast(handler.getName(), handler)
						.addLast(new PipelineErrorHandler(log, responseHeaders));
				}
			};
			// 创建两个工作组的线程 bossGroup与workerGroup
			NioEventLoopGroup bossGroup = new NioEventLoopGroup(1, new ExecutorThreadFactory("flink-rest-server-netty-boss"));
			NioEventLoopGroup workerGroup = new NioEventLoopGroup(0, new ExecutorThreadFactory("flink-rest-server-netty-worker"));

			/*************************************************
			 *  注释： 启动 Netty 网络通信 服务端引导程序
			 */
			bootstrap = new ServerBootstrap();
			bootstrap.group(bossGroup, workerGroup).channel(NioServerSocketChannel.class).childHandler(initializer);

			Iterator<Integer> portsIterator;
			try {
				portsIterator = NetUtils.getPortRangeFromString(restBindPortRange);
			} catch(IllegalConfigurationException e) {
				throw e;
			} catch(Exception e) {
				throw new IllegalArgumentException("Invalid port range definition: " + restBindPortRange);
			}

			// 注释： 绑定端口，通过轮询的方式来搞定
			int chosenPort = 0;
			while(portsIterator.hasNext()) {
				try {
					chosenPort = portsIterator.next();
					final ChannelFuture channel;
					if(restBindAddress == null) {
						channel = bootstrap.bind(chosenPort);
					} else {
						channel = bootstrap.bind(restBindAddress, chosenPort);
					}
					serverChannel = channel.syncUninterruptibly().channel();
					break;
				} catch(final Exception e) {
					// continue if the exception is due to the port being in use, fail early otherwise
					if(!(e instanceof org.jboss.netty.channel.ChannelException || e instanceof java.net.BindException)) {
						throw e;
					}
				}
			}

			if(serverChannel == null) {
				throw new BindException("Could not start rest endpoint on any port in port range " + restBindPortRange);
			}
			log.debug("Binding rest endpoint to {}:{}.", restBindAddress, chosenPort);
			final InetSocketAddress bindAddress = (InetSocketAddress) serverChannel.localAddress();
			final String advertisedAddress;
			if(bindAddress.getAddress().isAnyLocalAddress()) {
				advertisedAddress = this.restAddress;
			} else {
				advertisedAddress = bindAddress.getAddress().getHostAddress();
			}
			final int port = bindAddress.getPort();
			log.info("Rest endpoint listening at {}:{}", advertisedAddress, port);
			restBaseUrl = new URL(determineProtocol(), advertisedAddress, port, "").toString();

			restAddressFuture.complete(restBaseUrl);
			state = State.RUNNING;
			/*************************************************
			 *  注释：到此为止，主节点上的 WebMonitorEndpoint组件的Netty服务端起好了。
			 *  任务提交时： 启动 Netty 的客户端
			 */
			/*************************************************
			 *  注释： 启动
			 */
			startInternal();
		}
	}

2.6.3 startInternal();

Flink集群中的主节点中有三个重要的组件：ResourceManager、Dispatcher、WebMonitorEndpint，启动时均会进行选举，通过选举来触发该服务。

public void startInternal() throws Exception {

		/*************************************************
		 *  注释： 选举 ZooKeeperLeaderElectionService
		 *  不管你在那个地方见到这种格式的代码：leaderElectionService.start(this);
		 *  1、参与选举的 某个获胜的角色会调用： leaderElectionService.isLeader() ==> leaderContender.grantLeaderShip()
		 *  2、参与选举的 某个失败的角色会调用： leaderElectionService.notLeader()
		 */
		leaderElectionService.start(this);
		/*************************************************
		 *  注释： 开启定时任务
		 * executionGraphCache = DefaultExecutionGraphCach 清除已经执行完毕的ExecutionGraph
		 */
		startExecutionGraphCacheCleanupTask();
		if(hasWebUI) {
			log.info("Web frontend listening at {}.", getRestBaseUrl());
		}
	}

2.7 resourceManager启动

ResourceManager的启动主要分为以下：

• resourceManagerFactory.createResourceManager创建resourceManager对象，完成实例化之后会执行OnStart()方法[开启ResourceManager的服务]
• 开启两个心跳服务(监控JobManager与TaskManager的心跳)
• 开启两个定时任务(每隔30s检查TaskManager的心跳，每隔5min检查是否有申请slot的request超时未处理)

2.7.1 resourceManagerFactory.createResourceManager(实例化)

该方法创建 StandaloneResourceManager 实例对象，resourceManager = StandaloneResourceManager。在resourceManager的内部通过动态代理的方式构建了一个Rpc Server，用来处理TaskManager启动完成后，进行注册和心跳的请求服务。

public ResourceManager<T> createResourceManager(Configuration configuration, ResourceID resourceId, RpcService rpcService,
		HighAvailabilityServices highAvailabilityServices, HeartbeatServices heartbeatServices, FatalErrorHandler fatalErrorHandler,
		ClusterInformation clusterInformation, @Nullable String webInterfaceUrl, MetricRegistry metricRegistry, String hostname) throws Exception {
		final ResourceManagerMetricGroup resourceManagerMetricGroup = ResourceManagerMetricGroup.create(metricRegistry, hostname);
		final SlotManagerMetricGroup slotManagerMetricGroup = SlotManagerMetricGroup.create(metricRegistry, hostname);
		/*************************************************
		 *  注释： 创建 ResourceManagerRuntimeServices 实例
		 */
		final ResourceManagerRuntimeServices resourceManagerRuntimeServices = createResourceManagerRuntimeServices(configuration, rpcService,
			highAvailabilityServices, slotManagerMetricGroup);

		/*************************************************
		 *  注释： 创建 ResourceManager 实例
		 */
		return createResourceManager(configuration, resourceId, rpcService, highAvailabilityServices, heartbeatServices, fatalErrorHandler,
			clusterInformation, webInterfaceUrl, resourceManagerMetricGroup, resourceManagerRuntimeServices);
	}
// createResourceManager--> StandaloneResourceManagerFactory.createResourceManager
@Override
protected ResourceManager<ResourceID> createResourceManager(
		Configuration configuration,
		ResourceID resourceId,
		RpcService rpcService,
		HighAvailabilityServices highAvailabilityServices,
		HeartbeatServices heartbeatServices,
		FatalErrorHandler fatalErrorHandler,
		ClusterInformation clusterInformation,
		@Nullable String webInterfaceUrl,
		ResourceManagerMetricGroup resourceManagerMetricGroup,
		ResourceManagerRuntimeServices resourceManagerRuntimeServices) {

		final Time standaloneClusterStartupPeriodTime = ConfigurationUtils.getStandaloneClusterStartupPeriodTime(configuration);

		/*************************************************
		 *  注释： 得到一个 StandaloneResourceManager 实例对象
		 */
		return new StandaloneResourceManager(
			rpcService,
			resourceId,
			highAvailabilityServices,
			heartbeatServices,
			resourceManagerRuntimeServices.getSlotManager(),
			ResourceManagerPartitionTrackerImpl::new,
			resourceManagerRuntimeServices.getJobLeaderIdService(),
			clusterInformation,
			fatalErrorHandler,
			resourceManagerMetricGroup,
			standaloneClusterStartupPeriodTime,
			AkkaUtils.getTimeoutAsTime(configuration));
	}
// StandaloneResourceManager
public StandaloneResourceManager(RpcService rpcService, ResourceID resourceId, HighAvailabilityServices highAvailabilityServices,
		HeartbeatServices heartbeatServices, SlotManager slotManager, ResourceManagerPartitionTrackerFactory clusterPartitionTrackerFactory,
		JobLeaderIdService jobLeaderIdService, ClusterInformation clusterInformation, FatalErrorHandler fatalErrorHandler,
		ResourceManagerMetricGroup resourceManagerMetricGroup, Time startupPeriodTime, Time rpcTimeout) {

		/*************************************************
		 *  注释： 注意该父类方法
		 */
		super(rpcService, resourceId, highAvailabilityServices, heartbeatServices, slotManager, clusterPartitionTrackerFactory, jobLeaderIdService,
			clusterInformation, fatalErrorHandler, resourceManagerMetricGroup, rpcTimeout);

		// TODO_MA 注释：
		this.startupPeriodTime = Preconditions.checkNotNull(startupPeriodTime);
	}
// StandaloneResourceManager-->ResourceManager
public ResourceManager(RpcService rpcService, ResourceID resourceId, HighAvailabilityServices highAvailabilityServices,
		HeartbeatServices heartbeatServices, SlotManager slotManager, ResourceManagerPartitionTrackerFactory clusterPartitionTrackerFactory,
		JobLeaderIdService jobLeaderIdService, ClusterInformation clusterInformation, FatalErrorHandler fatalErrorHandler,
		ResourceManagerMetricGroup resourceManagerMetricGroup, Time rpcTimeout) {

		/*************************************************
		 *  注释： 当执行完毕这个构造方法的时候，会触发调用 onStart() 方法执行
		 */
		super(rpcService, AkkaRpcServiceUtils.createRandomName(RESOURCE_MANAGER_NAME), null);

		this.resourceId = checkNotNull(resourceId);
		this.highAvailabilityServices = checkNotNull(highAvailabilityServices);
		this.heartbeatServices = checkNotNull(heartbeatServices);
		this.slotManager = checkNotNull(slotManager);
		this.jobLeaderIdService = checkNotNull(jobLeaderIdService);
		this.clusterInformation = checkNotNull(clusterInformation);
		this.fatalErrorHandler = checkNotNull(fatalErrorHandler);
		this.resourceManagerMetricGroup = checkNotNull(resourceManagerMetricGroup);

		this.jobManagerRegistrations = new HashMap<>(4);
		this.jmResourceIdRegistrations = new HashMap<>(4);
		this.taskExecutors = new HashMap<>(8);
		this.taskExecutorGatewayFutures = new HashMap<>(8);

		this.jobManagerHeartbeatManager = NoOpHeartbeatManager.getInstance();
		this.taskManagerHeartbeatManager = NoOpHeartbeatManager.getInstance();

		this.clusterPartitionTracker = checkNotNull(clusterPartitionTrackerFactory).get(
			(taskExecutorResourceId, dataSetIds) -> taskExecutors.get(taskExecutorResourceId).getTaskExecutorGateway()
				.releaseClusterPartitions(dataSetIds, rpcTimeout).exceptionally(throwable -> {
					log.debug("Request for release of cluster partitions belonging to data sets {} was not successful.", dataSetIds, throwable);
					throw new CompletionException(throwable);
				}));
	}
//ResourceManager--> FencedRpcEndpoint
protected FencedRpcEndpoint(RpcService rpcService, String endpointId, @Nullable F fencingToken) {

		/*************************************************
		 *  注释：注意这个父类方法
		 */
		super(rpcService, endpointId);

		Preconditions.checkArgument(rpcServer instanceof FencedMainThreadExecutable, "The rpcServer must be of type %s.",
			FencedMainThreadExecutable.class.getSimpleName());

		// no fencing token == no leadership
		this.fencingToken = fencingToken;
		this.unfencedMainThreadExecutor = new UnfencedMainThreadExecutor((FencedMainThreadExecutable) rpcServer);
		this.fencedMainThreadExecutor = new MainThreadExecutor(getRpcService().fenceRpcServer(rpcServer, fencingToken),
			this::validateRunsInMainThread);
	}
//FencedRpcEndpoint--> RpcEndpoint
protected RpcEndpoint(final RpcService rpcService, final String endpointId) {
		this.rpcService = checkNotNull(rpcService, "rpcService");
		this.endpointId = checkNotNull(endpointId, "endpointId");

		/*************************************************
		 *  注释： 启动 ResourceManager 的 RPCServer 服务
		 *  启动的是 ResourceManager 的 Rpc 服务端。
		 *  在TaskManager启动好之后，接收注册和心跳的请求，来汇报Taskmanagaer的资源情况
		 *  通过动态代理构建一个Rpc Server
		 */
		this.rpcServer = rpcService.startServer(this);

		this.mainThreadExecutor = new MainThreadExecutor(rpcServer, this::validateRunsInMainThread);
	}
// 上述代码执行完成之后，实例化完成了，接下来就要执行ResourceManager中的onStart()方法，最终实现的是ResourceManager中的onStart()方法。
@Override
	public void onStart() throws Exception {
		try {

			/*************************************************
			 *  注释： 开启 RM 服务
			 */
			startResourceManagerServices();

		} catch(Exception e) {
			final ResourceManagerException exception = new ResourceManagerException(
				String.format("Could not start the ResourceManager %s", getAddress()), e);
			onFatalError(exception);
			throw exception;
		}
	}
// startResourceManagerServices
private void startResourceManagerServices() throws Exception {
		try {
			/*************************************************
			 *  注释：leaderElectionService = ZooKeeperLeaderElectionService
			 */
			leaderElectionService = highAvailabilityServices.getResourceManagerLeaderElectionService();

			// 注释：在 Standalone 模式下，什么也没做
			initialize();

			// 注释： 注意 this 对象
			// 注释： 执行选举，成功之后，调用 leaderElectionService.isLeader()
			// 注释： this = ResourceManager
			leaderElectionService.start(this);
			jobLeaderIdService.start(new JobLeaderIdActionsImpl());
			registerTaskExecutorMetrics();

		} catch(Exception e) {
			handleStartResourceManagerServicesException(e);
		}
	}
//-->leaderElectionService.start(this);
@Override
	public void start(LeaderContender newContender) throws Exception {
		if (contender != null) {
			// Service was already started
			throw new IllegalArgumentException("Leader election service cannot be started multiple times.");
		}

		contender = Preconditions.checkNotNull(newContender);

		// directly grant leadership to the given contender
		contender.grantLeadership(HighAvailabilityServices.DEFAULT_LEADER_ID);
	}
//-->contender.grantLeadership(HighAvailabilityServices.DEFAULT_LEADER_ID)
@Override
	public void grantLeadership(final UUID newLeaderSessionID) {

		/*************************************************
		 *  注释： 调用： tryAcceptLeadership 方法
		 */
		final CompletableFuture<Boolean> acceptLeadershipFuture = clearStateFuture
			.thenComposeAsync((ignored) -> tryAcceptLeadership(newLeaderSessionID), getUnfencedMainThreadExecutor());

		//注释： 调用 confirmLeadership
		final CompletableFuture<Void> confirmationFuture = acceptLeadershipFuture.thenAcceptAsync((acceptLeadership) -> {
			if(acceptLeadership) {
				// confirming the leader session ID might be blocking,
				leaderElectionService.confirmLeadership(newLeaderSessionID, getAddress());
			}
		}, getRpcService().getExecutor());

		//注释： 调用 whenComplete
		confirmationFuture.whenComplete((Void ignored, Throwable throwable) -> {
			if(throwable != null) {
				onFatalError(ExceptionUtils.stripCompletionException(throwable));
		}
		});
	}
//--> tryAcceptLeadership(newLeaderSessionID)
private CompletableFuture<Boolean> tryAcceptLeadership(final UUID newLeaderSessionID) {

		// T注释： 判断，如果集群有了 LeaderResourceManager
		if(leaderElectionService.hasLeadership(newLeaderSessionID)) {

			// 注释： 生成一个 ResourceManagerID
			final ResourceManagerId newResourceManagerId = ResourceManagerId.fromUuid(newLeaderSessionID);

			log.info("ResourceManager {} was granted leadership with fencing token {}", getAddress(), newResourceManagerId);

			//注释： 如果之前已成为过 Leader 的话，则清理之前的状态
			// clear the state if we've been the leader before
			if(getFencingToken() != null) {
				clearStateInternal();
			}
			setFencingToken(newResourceManagerId);

			/*************************************************
			 *  注释： 启动服务
			 *  1、启动心跳服务
			 *  	启动两个定时任务
			 *  2、启动 SlotManager 服务
			 *  	启动两个定时任务
			 */
			startServicesOnLeadership();

			return prepareLeadershipAsync().thenApply(ignored -> true);
		} else {
			return CompletableFuture.completedFuture(false);
		}
	}
//-->startServicesOnLeadership()
protected void startServicesOnLeadership() {

		/*************************************************
		 *  注释： 开启心跳服务
		 */
		startHeartbeatServices();
		/*************************************************
		 *  注释： 启动 SlotManagerImpl 只是开启了两个定时任务而已
		 */
		slotManager.start(getFencingToken(), getMainThreadExecutor(), new ResourceActionsImpl());
	}
//-->startHeartbeatServices
/*************************************************
	 *  注释： 当前 ResourceManager  启动了两个心跳服务：
	 *  1、taskManagerHeartbeatManager 心跳管理器 关心点的是： taskManager 的死活
	 *  2、jobManagerHeartbeatManager 心跳管理器 关心点的是： jobManager 的死活
	 *  taskManager 集群的资源提供者，任务执行者，从节点
	 *  jobManager 每一个job会启动的一个主控程序
	 *  不管是集群的从节点执行心跳，还是每一个job会启动的一个主控程序,都向 ResourceManager 去汇报
	 */
	private void startHeartbeatServices() {

		/*************************************************
		 *  注释： 用来收听： TaskManager 的心跳
		 */
		taskManagerHeartbeatManager = heartbeatServices
			.createHeartbeatManagerSender(resourceId, new TaskManagerHeartbeatListener(), getMainThreadExecutor(), log);

		/*************************************************
		 *  注释： 用来收听： JobManager 的心跳
		 */
		jobManagerHeartbeatManager = heartbeatServices
			.createHeartbeatManagerSender(resourceId, new JobManagerHeartbeatListener(), getMainThreadExecutor(), log);
	}
// 完成心跳服务的对象是HeartbeatManagerSenderImpl
// HeartbeatServices--HeartbeatManagerSenderImpl,调用的是类实例的 run() 方法的执行
HeartbeatManagerSenderImpl(long heartbeatPeriod, long heartbeatTimeout, ResourceID ownResourceID, HeartbeatListener<I, O> heartbeatListener,
		ScheduledExecutor mainThreadExecutor, Logger log, HeartbeatMonitor.Factory<O> heartbeatMonitorFactory) {
		super(heartbeatTimeout, ownResourceID, heartbeatListener, mainThreadExecutor, log, heartbeatMonitorFactory);
		this.heartbeatPeriod = heartbeatPeriod;

		/*************************************************
		 *  注释： 调度当前的类实例的 run() 方法的执行
		 *  执行的就是当前类的 run() 方法，当前只是一个调度任务
		 */
		mainThreadExecutor.schedule(this, 0L, TimeUnit.MILLISECONDS);
	}
//--run()
@Override
	public void run() {
		/*************************************************
		 *  注释： 在 Flink 的心跳机制中，跟其他的 集群不一样：
		 *  1、ResourceManager 发送心跳给 从节点 Taskmanager
		 *  2、从节点接收到心跳之后，返回响应
		 */
		// 注释： 实现循环执行
		if(!stopped) {
			log.debug("Trigger heartbeat request.");
			for(HeartbeatMonitor<O> heartbeatMonitor : getHeartbeatTargets().values()) {
				// 注释： ResourceManager 给目标发送(TaskManager 或者 JobManager)心跳
				requestHeartbeat(heartbeatMonitor);
			}
			/*************************************************
			 *  注释： 实现循环发送心跳的效果
			 */
			getMainThreadExecutor().schedule(this, heartbeatPeriod, TimeUnit.MILLISECONDS);
		}
	}
// --requestHeartbeat
/*************************************************
	 *  注释： HeartbeatMonitor 如果有从节点返回心跳响应，则会被加入到 HeartbeatMonitor
	 *  HeartbeatMonitor管理所有的心跳目标对象
	 */
	private void requestHeartbeat(HeartbeatMonitor<O> heartbeatMonitor) {
		O payload = getHeartbeatListener().retrievePayload(heartbeatMonitor.getHeartbeatTargetId());
		final HeartbeatTarget<O> heartbeatTarget = heartbeatMonitor.getHeartbeatTarget();

		/*************************************************
		 *  注释： 发送心跳 集群中启动的从节点(heartbeatTarget)
		 */
		heartbeatTarget.requestHeartbeat(getOwnResourceID(), payload);
	}
//--HeartbeatManagerImpl(requestHeartbeat)
	@Override
	public void requestHeartbeat(final ResourceID requestOrigin, I heartbeatPayload) {
		if(!stopped) {
			log.debug("Received heartbeat request from {}.", requestOrigin);

			/*************************************************
			 *  注释： 汇报心跳
			 */
			final HeartbeatTarget<O> heartbeatTarget = reportHeartbeat(requestOrigin);

			// 注释： 实现循环处理
			if(heartbeatTarget != null) {
				if(heartbeatPayload != null) {
					heartbeatListener.reportPayload(requestOrigin, heartbeatPayload);
				}
				heartbeatTarget.receiveHeartbeat(getOwnResourceID(), heartbeatListener.retrievePayload(requestOrigin));
			}
		}
	}

// 开启两个定时任务 slotManager.start
@Override
	public void start(ResourceManagerId newResourceManagerId, Executor newMainThreadExecutor, ResourceActions newResourceActions) {
		LOG.info("Starting the SlotManager.");

		this.resourceManagerId = Preconditions.checkNotNull(newResourceManagerId);
		mainThreadExecutor = Preconditions.checkNotNull(newMainThreadExecutor);
		resourceActions = Preconditions.checkNotNull(newResourceActions);

		started = true;

		/*************************************************
		 * 注释：开启第一个定时任务： checkTaskManagerTimeouts，检查 TaskManager 心跳
		 * taskManagerTimeout = resourcemanager.taskmanager-timeout = 30000
		 */
		taskManagerTimeoutCheck = scheduledExecutor
			.scheduleWithFixedDelay(() -> mainThreadExecutor.execute(() -> checkTaskManagerTimeouts()), 0L, taskManagerTimeout.toMilliseconds(),
				TimeUnit.MILLISECONDS);

		/*************************************************
		 *  注释开启第二个定时任务： checkSlotRequestTimeouts，检查SplotRequest超时处理
		 *  slotRequestTimeout = slot.request.timeout = 5L * 60L * 1000L
		 */
		slotRequestTimeoutCheck = scheduledExecutor
			.scheduleWithFixedDelay(() -> mainThreadExecutor.execute(() -> checkSlotRequestTimeouts()), 0L, slotRequestTimeout.toMilliseconds(),
				TimeUnit.MILLISECONDS);

		registerSlotManagerMetrics();
	}

2.7.2 resourceManager.start(启动)

自身给自身发一个START的消息，说明ResourceManager 已经成功启动完成。

resourceManager.start();
-->start
public final void start() {
		rpcServer.start();
	}
-->rpcServer.start()
    @Override
	public void start() {
		/*************************************************
		 *  注释： 发送 START 消息
		 *  只要发送了  START 这个消息，也就意味着： ResourceManager 已经成功启动好了。 
		 */
		rpcEndpoint.tell(ControlMessages.START, ActorRef.noSender());
	}

2.8 dispatcher启动

在老版本中直接创建一个 Dispatcher 对象然后调用 dispatcher.start() 来启动；新版 直接创建一个 DispatcherRunner， 内部就是要创建和启动 Dispatcher。启动过程主要有以下动作：

• 1.通过dispatcherRunnerFactory对象创建DispatcherRunner对象。
• 2.在实例化DispatcherRunner对象时会进行选举，选举成功会执行DispatcherRunner.isLeader()。
• 3.通过DefaultDispatcherRunner.grantLeadership方法构建Dispatcher对象，实例化完成之后会执行OnStart()方法。
• Dispatcher启动过程中会开启性能监控与引导程序的初始化。

2.8.1 dispatcherRunnerFactory.createDispatcherRunner(实例化)

dispatcherRunner = dispatcherRunnerFactory.createDispatcherRunner(highAvailabilityServices.getDispatcherLeaderElectionService(), fatalErrorHandler,
//注释： 注意第三个参数
new HaServicesJobGraphStoreFactory(highAvailabilityServices), ioExecutor, rpcService, partialDispatcherServices);
//-->createDispatcherRunner
@Override
	public DispatcherRunner createDispatcherRunner(
			// 注释： ZooKeeperLeaderElectionService
			LeaderElectionService leaderElectionService,
			FatalErrorHandler fatalErrorHandler,
			// 注释： HaServicesJobGraphStoreFactory
			JobGraphStoreFactory jobGraphStoreFactory,
			Executor ioExecutor,
			RpcService rpcService,
			PartialDispatcherServices partialDispatcherServices) throws Exception {
		//  注释： dispatcherLeaderProcessFactoryFactory = SessionDispatcherLeaderProcessFactoryFactory
		final DispatcherLeaderProcessFactory dispatcherLeaderProcessFactory = dispatcherLeaderProcessFactoryFactory.createFactory(
			jobGraphStoreFactory,
			ioExecutor,
			rpcService,
			partialDispatcherServices,
			fatalErrorHandler);
		/*************************************************
		 *  注释：
		 *  第一个参数：ZooKeeperLeaderElectionService
		 *  第四个参数：SessionDispatcherLeaderProcessFactoryFactory
		 */
		return DefaultDispatcherRunner.create(
			leaderElectionService,
			fatalErrorHandler,
			dispatcherLeaderProcessFactory);
	}
//--> DefaultDispatcherRunner.create()
public static DispatcherRunner create(LeaderElectionService leaderElectionService, FatalErrorHandler fatalErrorHandler,
		DispatcherLeaderProcessFactory dispatcherLeaderProcessFactory) throws Exception {
		/*************************************************
		 *  注释：
		 *  第一个参数： ZooKeeperLeaderElectionService
		 *  第三个参数： SessionDispatcherLeaderProcessFactoryFactory
		 */
		final DefaultDispatcherRunner dispatcherRunner = new DefaultDispatcherRunner(leaderElectionService, fatalErrorHandler,
			dispatcherLeaderProcessFactory);

		/*************************************************
		 *  注释： 开启 DispatcherRunner 的生命周期
		 *  第一个参数： dispatcherRunner = DefaultDispatcherRunner
		 *  第二个参数： leaderElectionService = ZooKeeperLeaderElectionService
		 */
		return DispatcherRunnerLeaderElectionLifecycleManager.createFor(dispatcherRunner, leaderElectionService);
	}
// DispatcherRunnerLeaderElectionLifecycleManager.createFor
public static <T extends DispatcherRunner & LeaderContender> DispatcherRunner createFor(T dispatcherRunner, LeaderElectionService leaderElectionService) throws Exception {

		/*************************************************
		 *  注释：
		 *  第一个参数： dispatcherRunner = DefaultDispatcherRunner
		 *  第二个参数： leaderElectionService = ZooKeeperLeaderElectionService
		 */
		return new DispatcherRunnerLeaderElectionLifecycleManager<>(dispatcherRunner, leaderElectionService);
	}
//--> DispatcherRunnerLeaderElectionLifecycleManager
private DispatcherRunnerLeaderElectionLifecycleManager(T dispatcherRunner, LeaderElectionService leaderElectionService) throws Exception {
		this.dispatcherRunner = dispatcherRunner;
		this.leaderElectionService = leaderElectionService;

		/*************************************************
		 *  注释： 启动选举
		 *  参数：dispatcherRunner = DefaultDispatcherRunner
		 *  调用对象：leaderElectionService = ZooKeeperLeaderElectionService
		 *  这个选举服务对象  leaderElectionService 内部的 leaderContender 是 ： DefaultDispatcherRunner
		 */
		leaderElectionService.start(dispatcherRunner);
		// leaderElectionService.start(this);
	}
//-->leaderElectionService.start(dispatcherRunner);
@Override
	public void start(LeaderContender contender) throws Exception {
		Preconditions.checkNotNull(contender, "Contender must not be null.");
		Preconditions.checkState(leaderContender == null, "Contender was already set.");

		LOG.info("Starting ZooKeeperLeaderElectionService {}.", this);

		synchronized(lock) {

			client.getUnhandledErrorListenable().addListener(this);

			// 注释： 取值根据实际情况而定
			leaderContender = contender;

			/*************************************************
			 *  注释：Fink的选举，和HBase一样都是通过 ZooKeeper的API框架Curator实现
			 *  1、leaderLatch.start(); 事实上就是举行选举
			 *  2、当选举结束的时候：
			 *  	如果成功了： isLeader()
			 *      如果失败了： notLeader()
			 */
			leaderLatch.addListener(this);
			leaderLatch.start();

			/*************************************************
			 *  注释： 注册监听器，如果选举结束之后：
			 *  1、自己成为 Leader, 则会回调 isLeader() 进行处理
			 *  2、自己成为 Follower，则会回调 notLeader() 进行处理
			 */
			cache.getListenable().addListener(this);
			cache.start();

			client.getConnectionStateListenable().addListener(listener);
			running = true;
		}
	}
//->选举成功，调用isLeader()方法
@Override
	public void isLeader() {
		synchronized(lock) {
			if(running) {
				issuedLeaderSessionID = UUID.randomUUID();
				clearConfirmedLeaderInformation();

				if(LOG.isDebugEnabled()) {
					LOG.debug("Grant leadership to contender {} with session ID {}.", leaderContender.getDescription(), issuedLeaderSessionID);
				}

				/*************************************************
				 *  注释： 分配 LeaderShip
				 *  leaderContender = JobManagerRunnerImpl
				 *  leaderContender = ResourceManager
				 *  leaderContender = DefaultDispatcherRunner
				 *  leaderContender = WebMonitorEndpoint
				 *  leaderElectionService.start(this);
				 *  leaderContender = this
				 */
				leaderContender.grantLeadership(issuedLeaderSessionID);

			} else {
				LOG.debug("Ignoring the grant leadership notification since the service has " + "already been stopped.");
			}
		}
	}

// DefaultDispatcherRunner.grantLeadership
@Override
	public void grantLeadership(UUID leaderSessionID) {

		/*************************************************
		 *  注释： 开启 Dispatcher 服务
		 */
		runActionIfRunning(() -> startNewDispatcherLeaderProcess(leaderSessionID));
	}
//startNewDispatcherLeaderProcess(leaderSessionID))
private void startNewDispatcherLeaderProcess(UUID leaderSessionID) {
		//  注释： 先停掉已有的
		stopDispatcherLeaderProcess();
		//  注释： SessionDispatcherLeaderProcess
		dispatcherLeaderProcess = createNewDispatcherLeaderProcess(leaderSessionID);
		final DispatcherLeaderProcess newDispatcherLeaderProcess = dispatcherLeaderProcess;
		/*************************************************
		 *  注释： 再启动一个新的
		 *  调用： SessionDispatcherLeaderProcess.start()
		 */
		FutureUtils.assertNoException(previousDispatcherLeaderProcessTerminationFuture.thenRun(newDispatcherLeaderProcess::start));
	}
//-->AbstractDispatcherLeaderProcess.start()
@Override
	public final void start() {

		/*************************************************
		 *  注释： 调用 startInternal()
		 */
		runIfStateIs(State.CREATED, this::startInternal);
	}
//--> startInternal()
	private void startInternal() {
		log.info("Start {}.", getClass().getSimpleName());
		state = State.RUNNING;

		// 注释： SessionDispatcherLeaderProcess
		onStart();
	}
//--> onStart()
 @Override
	protected void onStart() {

		/*************************************************
		 *  注释： 开启服务: 启动 JobGraghStore
		 *  一个用来存储 JobGragh 的存储组件
		 */
		startServices();

		//  注释： 到现在为止，依然还没有启动 Dispatcher
		onGoingRecoveryOperation = recoverJobsAsync()
			/*************************************************
			 *  注释： 运行: createDispatcherIfRunning()
			 */
			.thenAccept(this::createDispatcherIfRunning)
			.handle(this::onErrorIfRunning);
	}
//-->startServices
	private void startServices() {
		try {

			/*************************************************
			 *  注释： 开启 ZooKeeperJobGraphStore
			 */
			jobGraphStore.start(this);
		} catch (Exception e) {
			throw new FlinkRuntimeException(
				String.format(
					"Could not start %s when trying to start the %s.",
					jobGraphStore.getClass().getSimpleName(),
					getClass().getSimpleName()),
				e);
		}
	}
//-->createDispatcherIfRunning
private void createDispatcherIfRunning(Collection<JobGraph> jobGraphs) {
		runIfStateIs(State.RUNNING, () -> createDispatcher(jobGraphs));
	}
//->createDispatcher
private void createDispatcher(Collection<JobGraph> jobGraphs) {

		/*************************************************
		 *  调用对象： DefaultDispatcherGatewayServiceFactory
		 */
		final DispatcherGatewayService dispatcherService = dispatcherGatewayServiceFactory.create(
			// 注释： DispatcherID
			DispatcherId.fromUuid(getLeaderSessionId()),
			//注释： jobGraghs
			jobGraphs,
			//注释： ZooKeeperJobGraphStore
			jobGraphStore);DefaultDispatcherGatewayServiceFactory.
		completeDispatcherSetup(dispatcherService);
	}
// DefaultDispatcherGatewayServiceFactory.create
@Override
	public AbstractDispatcherLeaderProcess.DispatcherGatewayService create(DispatcherId fencingToken, Collection<JobGraph> recoveredJobs,
		JobGraphWriter jobGraphWriter) {

		// 注释： Dispatcher 的一个默认引导程序
		// 注释： 待恢复执行的 job 的集合
		final DispatcherBootstrap bootstrap = new DefaultDispatcherBootstrap(recoveredJobs);

		final Dispatcher dispatcher;
		try {
			/*************************************************
			 *  注释： 创建 Dispatcher
			 *  dispatcherFactory = SessionDispatcherFactory
			 */
			dispatcher = dispatcherFactory.createDispatcher(rpcService, fencingToken, bootstrap,
				// 注释： PartialDispatcherServicesWithJobGraphStore
		PartialDispatcherServicesWithJobGraphStore.from(partialDispatcherServices, jobGraphWriter));

		} catch(Exception e) {
			throw new FlinkRuntimeException("Could not create the Dispatcher rpc endpoint.", e);
		}

		/*************************************************
		 *  注释： Dispatcher 也是一个 RpcEndpoint 启动起来了之后，给自己发送一个 Hello 消息证明启动
		 */
		dispatcher.start();

		//  注释： 返回一个返回值
		return DefaultDispatcherGatewayService.from(dispatcher);
	}
//StandaloneDispatcher createDispatcher
@Override
	public StandaloneDispatcher createDispatcher(RpcService rpcService, DispatcherId fencingToken, DispatcherBootstrap dispatcherBootstrap,
		PartialDispatcherServicesWithJobGraphStore partialDispatcherServicesWithJobGraphStore) throws Exception {

		/*************************************************
		 *  注释： 构建一个 StandaloneDispatcher 返回
		 */
		// create the default dispatcher
		return new StandaloneDispatcher(rpcService, fencingToken, dispatcherBootstrap,
			DispatcherServices.from(partialDispatcherServicesWithJobGraphStore, DefaultJobManagerRunnerFactory.INSTANCE));
	}
// StandaloneDispatcher构造方法-->super()-->Dispatcher
public Dispatcher(RpcService rpcService, DispatcherId fencingToken, DispatcherBootstrap dispatcherBootstrap,
		DispatcherServices dispatcherServices) throws Exception {

		super(rpcService, AkkaRpcServiceUtils.createRandomName(DISPATCHER_NAME), fencingToken);
		checkNotNull(dispatcherServices);
		this.configuration = dispatcherServices.getConfiguration();
		this.highAvailabilityServices = dispatcherServices.getHighAvailabilityServices();
		this.resourceManagerGatewayRetriever = dispatcherServices.getResourceManagerGatewayRetriever();
		this.heartbeatServices = dispatcherServices.getHeartbeatServices();
		this.blobServer = dispatcherServices.getBlobServer();
		this.fatalErrorHandler = dispatcherServices.getFatalErrorHandler();
		this.jobGraphWriter = dispatcherServices.getJobGraphWriter();

		this.jobManagerMetricGroup = dispatcherServices.getJobManagerMetricGroup();
		this.metricServiceQueryAddress = dispatcherServices.getMetricQueryServiceAddress();

		this.jobManagerSharedServices = JobManagerSharedServices.fromConfiguration(configuration, blobServer, fatalErrorHandler);

		this.runningJobsRegistry = highAvailabilityServices.getRunningJobsRegistry();

		jobManagerRunnerFutures = new HashMap<>(16);

		this.historyServerArchivist = dispatcherServices.getHistoryServerArchivist();

		this.archivedExecutionGraphStore = dispatcherServices.getArchivedExecutionGraphStore();

		this.jobManagerRunnerFactory = dispatcherServices.getJobManagerRunnerFactory();

		this.jobManagerTerminationFutures = new HashMap<>(2);

		this.shutDownFuture = new CompletableFuture<>();

		this.dispatcherBootstrap = checkNotNull(dispatcherBootstrap);
	}
// 这儿执行完毕的时候，需要执行 onStart() 方法
@Override
	public void onStart() throws Exception {
		try {
			/*************************************************
			 *  注释： 启动 Dispatcher 服务
			 */
			startDispatcherServices();

		} catch(Exception e) {
			final DispatcherException exception = new DispatcherException(String.format("Could not start the Dispatcher %s", getAddress()), e);
			onFatalError(exception);
			throw exception;
		}

		/*************************************************
		 *  注释：  引导程序初始化
		 *  把所有中断的 job 恢复执行
		 */
		dispatcherBootstrap.initialize(this, this.getRpcService().getScheduledExecutor());
	}

//startDispatcherServices
private void startDispatcherServices() throws Exception {
		try 
			/*************************************************
			 *  注释： 性能监控的
			 */
			registerDispatcherMetrics(jobManagerMetricGroup);
		} catch(Exception e) {
			handleStartDispatcherServicesException(e);
		}
	}

//dispatcherBootstrap.initialize-->launchRecoveredJobGraphs-->dispatcher.runRecoveredJob
void runRecoveredJob(final JobGraph recoveredJob) {
		checkNotNull(recoveredJob);

		/*************************************************
		 *  注释： 调用 runJob 运行一个任务
		 */
FutureUtils.assertNoException(runJob(recoveredJob).handle(handleRecoveredJobStartError(recoveredJob.getJobID())));
	}
// runJob
private CompletableFuture<Void> runJob(JobGraph jobGraph) {
Preconditions.checkState(!jobManagerRunnerFutures.containsKey(jobGraph.getJobID()));
		/*************************************************
		 *  注释： 创建 JobManagerRunner
		 */
		final CompletableFuture<JobManagerRunner> jobManagerRunnerFuture = createJobManagerRunner(jobGraph);
		jobManagerRunnerFutures.put(jobGraph.getJobID(), jobManagerRunnerFuture);
		/*************************************************
		 *  注释： 启动 JobManagerRunner
		 */
		return jobManagerRunnerFuture.thenApply(
			// 提交任务 == start JobManagerRunner
			FunctionUtils.uncheckedFunction(this::startJobManagerRunner)

		).thenApply(
			FunctionUtils.nullFn()
		).whenCompleteAsync(
			(ignored, throwable) -> {
				if(throwable != null) {
					jobManagerRunnerFutures.remove(jobGraph.getJobID());
				}
			}, getMainThreadExecutor());
	}

3.总结

• Flink集群的主节点包含的重要组件：ResourceManager、Dispatcher、JobManger以及WebMonitorEndpoint。
  • ResourceManager主要负责集群资源的调度管理
  • JobManger是主控程序，负责具体的Job执行，在一个集群可能存在多个JobManger同时执行。
  • Dispatcher主要是接收用户提交的JobGraph，随后启动一个JobManager负责当前job的执行
  • WebMonitorEndpoint里维护了很多的Handler，客户端提交的作业都是由webMonitor来接收，并决定使用哪个Handler进行处理
• Flink集群中主节点的启动主要做了以下的事情
  • 解析传入参数以及flink配置文件的参数
  • 初始化相关的服务
    • commonRpcServices: 基于Akka的RpcService实现
    • haServices：HA相关服务
    • blobServer：处理大文件的服务
    • heartbeatServices：提供心跳所需的所有服务
    • metricRegistry：性能监控服务
    • archivedExecutionGraphStore：存储ExecutionGraph的可序列化形式
  • 启动ResourceManager
  • 启动Dispatcher
  • 启动WebMonitorEndpoint
• flink集群的主节点中运行这ResourceManager、Dispatcher、WebMonitorEndpoint；当客户端向Flink集群提交作业时(客户端会事先构建好JobGraph)，由Dispatcher启动柜一个新的JobManager，同时JobManager会向ResourceManager申请运行该Job所需的集群资源。
• Flink集群直接点启动的入口是StandaloneSessionClusterEntryPoint
• WebMonitor的启动(standalone)：由restEndpointFactory创建restEndpoint实对象，随后启动WebMonitor对象，在该对象中会初始化很多的Handler用来处理各种请求，同时启动Netty服务端，启动完成后会有选举的动作
• ResourceManager的启动：通过resourceManagerFactory.createResourceManager构建resourceManager对象，完成实例化后会执行OnStart()方法，会启动RpcServer服务(主要是为了TaskManager启动完成后进行注册和心跳服务)，同时会进行选举，选举成成功会执行LeaderShipService.IsLeader()，且会开启两个心跳服务以及两个定时任务。
• Dispatcher启动：1.通过dispatcherRunnerFactory对象创建DispatcherRunner对象。2.在实例化DispatcherRunner对象时会进行选举，选举成功会执行DispatcherRunner.isLeader()。3.通过DefaultDispatcherRunner.grantLeadership方法构建Dispatcher对象，实例化完成之后会执行OnStart()方法。Dispatcher启动过程中会开启性能监控与引导程序的初始化(恢复中断的作业)。