Scaffold EVPN Fabric Resource and Controller

[felix-kaestner]

This high-level CRD will take care of creating and managing all low-level resources that are required to build a EVPN VXLAN resource.

Its controller implementation is intentionally left empty to a large extend to be extended by future changes. The setup constructs a list of sub-reconciler functions that are called in sequence to build up the full lifecycle of the Fabric.

[nikatza]

Looks good to me :) The API is self-contained and explanatory, conventions also (the Unnumbered bool had let me thinking for a bit), the reconciler logic is also fitting for the purpose of this PR.

Before we merge I would like to sync on this issue: I am wondering if we would want to have a more modular and extendable design for the fabric type. For example, by default we could have a "plain routed" fabric with just deviceSelector, loopbacks, and underlay. Then, we could extend it with references to a specialized type, similar to what we do with the core types. Like this we could have support different fabrics, ike the current EVPN-VXLAN, EVPN MPLS, etc. Some of these fabrics would be reusing some types.

Obviously the evpn self-contained group is quite appealing too and eventually also the straight-forward way to go.

Thanks for opening this PR, looking forward 🚀

[nikatza]

I quite like this API definition, it is straightforward and self-explanatory. I think thought, that there are some assumptions being made and that are not clear/documented: e.g., one device and all sub-resources belong to just one fabric. Either if this holds of not, I think we would benefit from either adding a concept, or extending its documentation.

[nikatza]

We currently wouldn't prevent a user defining two fabrics, with label selectors that intersect on some devices. This would result in a competition for the sub-resources and would potentially lead to an outage. At the same time, I understand that if we support two fabrics, some devices might actually need to be in both. I think the question in that case is, how do we ensure that a single brick is indirectly managed by just one fabric? should we also label the sub resources?