LoadBalancer IPAM: support IP assignment with `Service.spec.externalIPs/loadBalancerIP`

[defo89]

We use Calico for BGP peering and announcing Service IPs to the upstream fabric.

BGPConfiguration allows Services from pre-defined ranges to be used and announced:

› kubectl get bgpconfiguration default -oyaml | yq .spec.serviceLoadBalancerIPs
- cidr: 10.10.10.0/24
- cidr: 192.168.0.0/27

It would be great if Loadbalancer controller would not only tolerate projectcalico.org/loadBalancerIPs for manual assignment but also actual Service.spec.externalIPs and Service.spec.loadBalancerIP.

This would help to gradually migrate existing charts when payload is deployed to clusters where Calico LoadBalancer IP address management is used without having to switch the whole chart fleet to the Calico-specific annotation.

[caseydavenport]

Agree this would be nice to do.

[MichalFupso]

The Service.spec.loadBalancerIP is deprecated in upstream API, that's why we went with the annotation to specify which IPs need to be assigned to the service.

For the Service.spec.externalIPs I think the use case is not for Calico kube-controller to assign those specific IPs to the service, but rather update the service.Status with those IPs that are managed externally. I agree that would be a nice addition