Master Server.
- provide Grpc/http api, including
  - operate cluster
    - register/delete executor server
    - handle heartbeat (keep alive)
  - user interface
    - submit job
    - query job(s)
    - cancel job
  - schedule and failover jobs
ExecutorManager
- Handle Heartbeat
  - Notify Resource Manager updates the status infos
- Maintain the aliveness of Executors.
  - Check liveness
    - Executor Manager check every executor whether the heartbeat has been timeout.
    - Once an executor is offline by heartbeat timeout, it should notify the job manager to reschedule all the tasks on it.
Executor Client
- Embeds two independent interfaces
  - ExecutorServiceClient, which is used to dispatch task to executor.
  - BrokerServiceClient, which is used to manage resource belongs to an executor.
JobManager
- Receive SubmitJob Request, Check the type of Job, Create the JobMaster.
- JobMaster (per job)
  - Generate the Tasks for the job
  - Schedule and Dispatch Tasks