NIFI-7592: Allow NiFi to be started without a GUI/REST interface

[mattyb149]

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Description of PR

New and improved version of a previous PR to move NARs and dependencies around such that NiFi could be started in a "headless" mode. Specifically it removes the requirement on JettyServer and instead moves that into nifi-server-nar and provides a reference implementation for a headless NiFi in nifi-headless-server-nar.

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[alopresto]

Thanks Matt. I will take a look soon but very excited to get this contribution.

[markap14]

I'll review this as well.

[markap14]

So far, from my perspective things look good @mattyb149 . One thing that I noticed, though, is that if you have processors that are stopped, the headless mode will go ahead and run those. Which makes sense because there's no way to start/stop the processors. But if the processor depends on a controller service, those controller services don't get automatically enabled. Do you think it makes sense to go ahead and enable Controller Services before starting the processors?

[mattyb149]

Yeah makes sense for headless to enable the controller services since there's no UI to enable them. Then any dependent processors can start as you mentioned. Will add

[bbende]

Overall looks good, left a couple of minor comments.

One other comment is that there is a lot of overlap of dependencies between nifi-framework-nar and nifi-server-nar, and I'm wondering if we could reduce most of the dependencies in nifi-server-nar to include just the WARs and get everything else from the parent.

[bbende]

Updates look good, going to merge, thanks!