Better support for HA JobTrackers

[tarnfeld]

I've not got this up and running yet, so just thinking it through. It'd be great (and a requirement for me) to support HA jobtrackers. I think there are a couple of small issues that currently prevent that, though please correct me if i'm wrong. Is anyone else successfully running HA JobTrackers on Mesos?

• Don't set the mapred.job.tracker option to a host:port combo. This isn't how HA jobtrackers work, you list (elsewhere in configuration) the name:host:port combo's and reference them with an alias here. Due to the way the configuration is passed to the TaskTrackers, the only issues I can find here is Don't set the mapred.job.tracker config option #27. I can confirm with this fix applied I can at least get TT's to launch and run with HA jobtracker config.
• Allow all JobTracker's to register with the same Mesos framework ID. When using the automatic JobTracker failover (using the ZooKeeper Failover Controller) feature hadoop will keep all jobs and tasks running, however I think due to the fact each MesosScheduler will register with it's own framework identifier all the TaskTrackers will be killed. If they both register and use a large failover timeout, would this issue be solved?

Looking forward to anyone's thoughts...