Allow empty services

[chrispruitt]

What does this PR do?

This enables the nomad provider the ability to allow empty services. For instance, when a service is scaled down to 0 the route will persist. This would be an opt-in feature (false by default).
Fixes #10374

Motivation

I currently have services in Nomad that scaled down to zero and use a port-knocking solution that scales the service up when the route receives traffic. Also, the Kubernetes provider already has this option, so I felt like it was missing from the nomad provider.

More

• Added/updated tests
• Added/updated documentation

Additional Notes

I attempted to implement this just like the Kubernetes provider for consistency.
Also, to make this possible, I had to utilize Nomad's job API methods, rather than the service API methods to retrieve the list of existing services. This is because Nomad does not currently list nonregistered services (or services scaled to 0) with service API methods.

[mmatur]

Thanks a lot for this contribution @chrispruitt

Few comments below

[mmatur]

Hi @chrispruitt

Thanks for your changes. Seems good to me regarding the feature.

I am one more question what do you think to use a mock instead of creating these fixtures files for test?

[chrispruitt]

@mmatur I just followed the same process this provider package already had in place. The only change I made was moving the JSON responses to files. I don't have a strong opinion either way. They do end up with the same result in my opinion and the fixtures approach is easy to track mocked responses IMO.

On another note, do I need to rebase this branch? Or would you do that before merging? Thanks!

[mmatur]

Thanks for your feedback @chrispruitt .

Let's move forward with that and see what other maintainers think about it

I gave it a try and it seems good to me

LGTM

[nmengin]

Thank you @chrispruitt for this contribution!

LGTM 👏

[chrispruitt]

Are we able to get one more approval and merge this guy???

Thanks!

[rtribotte]

Thanks 👌