Fix multi-interface networking in the system scheduler

[neilmock]

This was originally mentioned in #8208 (comment), and purportedly fixed in #8230, but we noticed our system job appeared to bind on all interfaces instead of the specified host_network.

We noticed we were always evaluating to the first half of this conditional which didn't seem right:

nomad/client/allocrunner/networking_cni.go

Line 170 in 4ba3afa

if len(alloc.AllocatedResources.Shared.Ports) == 0 && len(alloc.AllocatedResources.Shared.Networks) > 0 {

This is a proposed fix, it seems correct given previous discussion but we are new to Nomad internals.

[hashicorp-cla]

All committers have signed the CLA.

[notnoop]

Thank you very much for this contribution. Any chance you can add a test as well?

[neilmock]

Thank you very much for this contribution. Any chance you can add a test as well?

I may not have the bandwidth to test this fully, as I don't think much of the multi-interface networking code is under coverage at the moment; e.g. we are also seeing issues with multi-interface IP assignment in Consul service registrations (which we have patched in our fork). But I'm very much willing to collaborate on the effort to wrangle these bugs.

[nickethier]

Thanks @neilmock I'll take on trying to get this tested a bit better. I'd love to hear more about any other patches you've made wrt multi-interface IP networking.

[neilmock]

Thanks @neilmock I'll take on trying to get this tested a bit better. I'd love to hear more about any other patches you've made wrt multi-interface IP networking.

We haven't done much, but we did put in a hack to make Consul register the correct host IP/interface for services. You can see a diff here.

master...getenv:getenv

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