bjq: add operator set-config ability and ability to manage multiple queues

[mismithhisler]

Description

These changes add the batch queue manager which allows the nomad server to manage various queues for both the global scheduler config, and various node pool scheduler configs (Enterprise feature). This change allows the nomad operator scheduler set-config to update queue's for a running server.

Testing & Reproduction steps

Links

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Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

[allisonlarson]

I know I'll have more questions, but starting out with a couple of them

[allisonlarson]

This seems like its changing my mental model of the queue's lifecycles, but I can't tell if its an issue or not. If we create a new set of queues when this is enabled, do we lose anything? I think at some point there was a comment about rebuilding the state during the SetEnabled call, but that might have been misplaced?

[mismithhisler]

Yeah similar to eval broker and deployments watcher, the Nomad server isn't going to be doing this work if it's not the leader. Once a server becomes the leader, it's actually going to do the eval broker logic, and in this case, it's going to build it's queue state and actually start processing the queue.

[allisonlarson]

If a queue is updated, does it loose all of the queued workloads still waiting? I think thats the nagging question I didn't have words for in my previous review (sorry!)

[mismithhisler]

It does, but then it would be rebuilt when the new queue gets started. That's probably not as efficient as an in place update of an existing queue, but I figured we could revisit if this actually needs better performance?

But now that I'm looking at this after a couple days I'm noticing some issues with how we wait for job placement and how we use Stop() that need to be fixed.