Add the ability to add a secondary load balancer to the control plane

[vincepri]

/kind feature
/assign
/priority important-soon

Describe the solution you'd like
In a lot of topologies, the control plane has a public and internal load balancer. Currently the AWSCluster CRD offers only ways to configure a single control plane.

Given the long term proposal for an AWSNetwork CRD to address the current shortcomings of AWSCluster, I'd like to propose to add a way to create and attach also a secondary load balancer, configured by the user, and limited only to NLB or ALB (aka elbv2, not classic) load balancer types.

There are a few options we can consider, currently leaning towards the first one:

• [preferred] Add a SecondaryControlPlaneLoadBalancer field alongside the ControlPlaneLoadBalancer one and take into account of the new field and behavior in the current elb scopes and reconcilers.
  • This would be a backward compatible change.
  • The code changes should not be too invasive, and can be made in a next minor release.
  • Compatible with ClusterClass and SSA.
• Add a list of AdditionalControlPlaneLoadBalancers alongside the ControlPlaneLoadBalancer.
  • Requires a CRD breaking change to support SSA and ClusterClass if we want to reuse the struct in ControlPlaneLoadBalancer, given that the name is optional.
  • Unclear if more than two load balancers for the control plane is useful at all.
  • Handling a large number of load balancer and storing their information might be tricky.

cc @richardcase @JoelSpeed @nrb

[vincepri]

/triage accepted

[nrb]

/assign @nrb

[richardcase]

There have been a few asks related to this, tagging for future reference: #2849 and #1484

[nrb]

/milestone v2.3.0

[k8s-ci-robot]

@nrb: You must be a member of the kubernetes-sigs/cluster-api-provider-aws-maintainers GitHub team to set the milestone. If you believe you should be able to issue the /milestone command, please contact your Cluster API Provider AWS Maintainers and have them propose you as an additional delegate for this responsibility.

In response to this:

/milestone v2.3.0

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[k8s-triage-robot]

This issue is labeled with priority/important-soon but has not been updated in over 90 days, and should be re-triaged.
Important-soon issues must be staffed and worked on either currently, or very soon, ideally in time for the next release.

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• Deprioritize it with /priority important-longterm or /priority backlog
• Close this issue with /close

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/remove-triage accepted