Consul with CNI and host_network addresses

[nickethier]

This PR implements a new service and check address_mode named alloc. The alloc service address mode signals that the address used when making Consul service and check registrations should be derived from the allocation's network namespace. This enables addresses which are created via CNI to be registered directly with Consul rather than having to expose them through Nomad's port mapping.

I added some validation to error when this mode is uses with service blocks under a task.

This PR also uses the correct host_network address when registering in host/default mode.

fixes #8801
fixes #8698

[shoenig]

Looks like a number of tests are gonna need newGroupServiceHook.networkStatusGetter set

[shoenig]

LGTM!

[Legogris]

This looks really promising :)

@tgross @schmichael I see this is slated for 1.0 - what are your thoughts on releasing a 0.12.8 with this included? Could make the upgrade path to 1.0 a lot smoother I think.

[tgross]

Hi @Legogris generally speaking we don't backport features to previous versions of Nomad, only critical bugs and security patches.

[Legogris]

@tgross This is a bugfix, no? Given that only with this change is it possible (hopefully!) to get the mapping between services and IPs working as documented when running with Consul (this has been broken since 0.12 as brought up in several issues). I don't know how representative we are but this is a significant one here.

[Legogris]

@nickethier Since you've been the one mostly working on this, what's your stance on the above?

Just so there's no confusion, using host_network configuration with 0.12.8 is currently registering corresponding Consul services under arbitrary IP addresses and the feature (which was introduced in 0.12) is therefore unusable together with Consul.

[github-actions]

I'm going to lock this pull request because it has been closed for 120 days ⏳. This helps our maintainers find and focus on the active contributions.
If you have found a problem that seems related to this change, please open a new issue and complete the issue template so we can capture all the details necessary to investigate further.