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== State Diagram ==
GroomServer state includes
* NORMAL: Everything works fine.
* STALE: This happens when DiskErrorException is thrown.
* DENIED: This indicates failing to establish connection to BSPMaster.
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== Components ==
* Registrator: Register to GroomManager
* TaskManager: Perform tasks management.
* Launch a task.
* Stop a task.
* Kill a task.
* Resume a task.
* Monitor: Report GroomServer and tasks related information.
GroomServer is a process whose main responsibility is to manage bsp tasks. In addition to task management, GroomServer collaborates with BSPMaster so that job execution can be done correctly. Works that GroomServer performs include:
- Check local disk:
- Check local disk if writable.
Delete files under local dir (bsp.local.dir)
- Clear state table:
- Start http server: An embedded http service.
- Start worker server: RPC service listens to master's direction.
Register to BSPMaster: Enroll itself to BSPMaster with GroomServerStatus.
- Start message dispatcher (Instructor): (TODO: refactor needed)
- Start monitor service: A process export metrics, task status, etc. information.
receives instructions from BSPMasters.
- spawns one or more tasks as separated jvm processes where tasks are then executed.
monitors spawned processes via ping; when a task is
out of contact (failure/ crashed): launch a new process and restart the task with max attempt set to 3
exceeding max attempt: update task status/ notify BSPMasters
sends heartbeat to BSPMasters
A GroomServer forks a new task.
The spawned task ack with metrics to GroomServer.
Upon reception of task's ack, the GroomServer exports metrics to monitor system.
- A task failure event happens.
A corresponded GroomServer detects the task failure.
The GroomServer tries to restart the task.
If failing restart, the GroomServer export by marking the task as failed.