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[YARN] MRAppMaster心跳原理

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hackshell

最近集群遇到一个问题,就是集群在跑任务的时候,AM会超时10min而被KILL,但任务重跑则成功,问题是随机的出现的, 所以初步怀疑是因为AM心跳汇报出现问题或则RM因为繁忙hang住,AM因为某些机制导致等待10min不汇报心跳 ,所以我们还是先了解,AM是如何向RM汇报心跳的。

在MRAppMaster中,ContainerAllocatorRouter负责向RM申请资源(发送心跳)

[YARN] MRAppMaster心跳原理

RMContainerAllocator其最终父类是RMCommunicator,它实现了RMHeartbeatHandler接口

public interface RMHeartbeatHandler {   long getLastHeartbeatTime(); // 获取上一次心跳的时间   void runOnNextHeartbeat(Runnable callback); // 回调注册到callback队列的callback函数 } 

每一次心跳回来,都会执行一次注册在heartbeatCallbacks中的回调函数:

allocatorThread = new Thread(new Runnable() {  @Override  public void run() {    while (!stopped.get() && !Thread.currentThread().isInterrupted()) {     ......     heartbeat();       lastHeartbeatTime = context.getClock().getTime();// 记录上一次心跳时间     executeHeartbeatCallbacks(); // 执行回调函数     .... });  

RMCommunicator类中:

private void executeHeartbeatCallbacks() {     Runnable callback = null;     while ((callback = heartbeatCallbacks.poll()) != null) {       callback.run();     }   } 

在RMCommunicator启动时, 首先会向RM注册 ,把自己的host和port告诉RM,然后在启动一条线程(startAllocatorThread)定期的调用 RMContainerAllocator中实现的heartbeat方法 (向RM申请资源,定期汇报信息,告诉RM自己还活着)。

AM初始化同时也会初始化RMCommunicator:

protected void serviceStart() throws Exception {   scheduler= createSchedulerProxy(); // 获取RM的代理   register(); // 注册   startAllocatorThread(); // 心跳线程 .... } 

AM的ContainerAllocatorRouter事件处理流程如下图:

[YARN] MRAppMaster心跳原理

注册流程:

调用RMCommunicator远程调用ApplicationMasterService的registerApplicationMaster方法,设置维护responseId,然后把它加入AMLivelinessMonitor中,并使用map记录时间,用来监控AM是否因为长时间没有心跳而超时,如果AM长时间没有心跳信息更新,RM就会通知NodeManager把AM移除。

心跳线程:

在发送心跳的过程中,即也是获取资源的过程

@Override   protected synchronized void heartbeat() throws Exception {     scheduleStats.updateAndLogIfChanged("Before Scheduling: ");     List<Container> allocatedContainers = getResources();// 重要的方法     if (allocatedContainers.size() > 0) {       scheduledRequests.assign(allocatedContainers);     }    ......   } 

获取资源的过程:

private List<Container> getResources() throws Exception {  ...  response = makeRemoteRequest(); // 和RM进行交互  ...  // 优先处理RM发送过来的命令  if (response.getAMCommand() != null) {      switch(response.getAMCommand()) {     case AM_RESYNC:     case AM_SHUTDOWN:      eventHandler.handle(new JobEvent(this.getJob().getID(),          JobEventType.JOB_AM_REBOOT));      throw new YarnRuntimeException("Resource Manager doesn't recognize AttemptId: " +          this.getContext().getApplicationID());     default:      ....   }  // 等等一系列处理 } }  

构建请求:

protected AllocateResponse makeRemoteRequest() throws IOException {     AllocateRequest allocateRequest =         AllocateRequest.newInstance(lastResponseID,           super.getApplicationProgress(), new ArrayList<ResourceRequest>(ask),           new ArrayList<ContainerId>(release), blacklistRequest);     AllocateResponse allocateResponse;     allocateResponse = scheduler.allocate(allocateRequest); // RPC调用ApplicationMasterService的allocate方法     ..... } 

每一次心跳的调用都会刷新AMLivelinessMonitor的时间,代表AM还活着

而且我们通过代码可以看出,资源请求被封装为一个ask,即一个ResourceRequest的ArrayList的资源列表 例如:

priority:20 host:host9 capability:<memory:2048, vCores:1> priority:20 host:host2 capability:<memory:2048, vCores:1> priority:20 host:host10 capability:<memory:2048, vCores:1> priority:20 host:/rack/rack3203 capability:<memory:2048, vCores:1> priority:20 host:/rack/rack3202 capability:<memory:2048, vCores:1> priority:20 host:* capability:<memory:2048, vCores:1> 

然而,ask是如何被构造的呢?

RMContainerAllocator中的addMap,addReduce,assign方法中对ask的数据内容进行了修改

addContainerReq --> addResourceRequest --> addResourceRequestToAsk; 

通过在代码自己添加日志可以看出,资源会被分为local,rack,和any级别去申请资源

最终变为一个ask list发送到RM上:

 ask Capability:<memory:2048, vCores:1> ResourceName:* NumContainers:384 Priority:20 RelaxLocality:true  ask Capability:<memory:2048, vCores:1> ResourceName:/rack/rack3201 NumContainers:227 Priority:20 RelaxLocality:true  ask Capability:<memory:2048, vCores:1> ResourceName:/rack/rack3202 NumContainers:231 Priority:20 RelaxLocality:true  ask Capability:<memory:2048, vCores:1> ResourceName:/rack/rack3203 NumContainers:152 Priority:20 RelaxLocality:true  ask Capability:<memory:2048, vCores:1> ResourceName:/rack/rack3204 NumContainers:158 Priority:20 RelaxLocality:true  ask Capability:<memory:2048, vCores:1> ResourceName:host1 NumContainers:46 Priority:20 RelaxLocality:true  ask Capability:<memory:2048, vCores:1> ResourceName:host5 NumContainers:52 Priority:20 RelaxLocality:true  ask Capability:<memory:2048, vCores:1> ResourceName:host6 NumContainers:38 Priority:20 RelaxLocality:true 

类似日志为:

getResources() for application_1438330253091_0004: ask=29 release= 0 newContainers=0 finishedContainers=0 resourcelimit=<memory:0, vCores:0> knownNMs=24 
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