KEP-1645: define dual stack policies and fields

[MrFreezeex]

• One-line PR description: Define dual stack recommendations and fields

• Issue link: Multi-Cluster Services API #1645

• Other comments: This does three things: define initial suggestion as to what an implementation may do to support dual stack services, fix the max items for the IPs field (which is already fixed in the actual CRD) and add a IPfamilies matching the same field in the Service that implementation may use to reconcile this globally with an implementation defined policy.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: MrFreezeex
Once this PR has been reviewed and has the lgtm label, please assign skitt for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• keps/sig-multicluster/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[ryanzhang-oss]

AFAIK, IPV4 and IPV6 format are quite different, are the formats in the "ips" field alone not enough for the consumer to discern? I assume that the consumer knows what IP family it can support.

[MrFreezeex]

This field is more aimed toward the allocation of the IPs than what happens after the IPs are already actually allocated a bit like the current type field or even how the ipFamilies field behave on a regular Service.

For instance for Cilium we would most likely want to do an intersection of all the ipFamilies in the exported Services which would put this as relevant as the other fields to "allocate" the IPs (meaning to create the derived service as it how we do this) to us essentially.