Package org.apache.hadoop.yarn.applications.distributedshell

Class ApplicationMaster

java.lang.Object
org.apache.hadoop.yarn.applications.distributedshell.ApplicationMaster
@Public @Unstable public class ApplicationMaster extends Object
An ApplicationMaster for executing shell commands on a set of launched containers using the YARN framework.

This class is meant to act as an example on how to write yarn-based application masters.

The ApplicationMaster is started on a container by the ResourceManager's launcher. The first thing that the ApplicationMaster needs to do is to connect and register itself with the ResourceManager. The registration sets up information within the ResourceManager regarding what host:port the ApplicationMaster is listening on to provide any form of functionality to a client as well as a tracking url that a client can use to keep track of status/job history if needed. However, in the distributedshell, trackingurl and appMasterHost:appMasterRpcPort are not supported.

The ApplicationMaster needs to send a heartbeat to the ResourceManager at regular intervals to inform the ResourceManager that it is up and alive. The ApplicationMasterProtocol.allocate(org.apache.hadoop.yarn.api.protocolrecords.AllocateRequest) to the ResourceManager from the ApplicationMaster acts as a heartbeat.

For the actual handling of the job, the ApplicationMaster has to request the ResourceManager via AllocateRequest for the required no. of containers using ResourceRequest with the necessary resource specifications such as node location, computational (memory/disk/cpu) resource requirements. The ResourceManager responds with an AllocateResponse that informs the ApplicationMaster of the set of newly allocated containers, completed containers as well as current state of available resources.

For each allocated container, the ApplicationMaster can then set up the necessary launch context via ContainerLaunchContext to specify the allocated container id, local resources required by the executable, the environment to be setup for the executable, commands to execute, etc. and submit a StartContainerRequest to the ContainerManagementProtocol to launch and execute the defined commands on the given allocated container.

The ApplicationMaster can monitor the launched container by either querying the ResourceManager using ApplicationMasterProtocol.allocate(org.apache.hadoop.yarn.api.protocolrecords.AllocateRequest) to get updates on completed containers or via the ContainerManagementProtocol by querying for the status of the allocated container's ContainerId.

After the job has been completed, the ApplicationMaster has to send a FinishApplicationMasterRequest to the ResourceManager to inform it that the ApplicationMaster has been completed.

  • Field Details

    • appAttemptID

      @VisibleForTesting protected ApplicationAttemptId appAttemptID

    • numTotalContainers

      @VisibleForTesting protected int numTotalContainers

    • numAllocatedContainers

      @VisibleForTesting protected AtomicInteger numAllocatedContainers

    • numRequestedContainers

      @VisibleForTesting protected AtomicInteger numRequestedContainers

    • numIgnore

      protected AtomicInteger numIgnore

    • totalRetries

      protected AtomicInteger totalRetries

    • launchedContainers

      @VisibleForTesting protected final Set<ContainerId> launchedContainers

  • Constructor Details

    • ApplicationMaster

      public ApplicationMaster()

  • Method Details

    • main

      public static void main(String[] args)
      Parameters:
      args - Command line args

    • init

      public boolean init(String[] args) throws org.apache.commons.cli.ParseException, IOException
      Parse command line options
      Parameters:
      args - Command line args
      Returns:
      Whether init successful and run should be invoked
      Throws:
      org.apache.commons.cli.ParseException
      IOException

    • cleanup

      protected void cleanup()

    • run

      public void run() throws YarnException, IOException, InterruptedException
      Main run function for the application master
      Throws:
      YarnException
      IOException
      InterruptedException

    • finish

      @VisibleForTesting protected boolean finish()

    • getRelativePath

      public static String getRelativePath(String appName, String appId, String fileDstPath)