+++ This bug was initially created as a clone of Bug #2045576 +++ kube 1.23 introduced a breaking API change in dual-stack services which I'm just noticing now... In kube 1.21 and 1.22 (OCP 4.8 and 4.9), the apiserver would default the value of `ipFamilyPolicy` to `RequireDualStack` if you created a Service with two `ipFamilies` or two `clusterIPs` but no explicitly-specified `ipFamilyPolicy`: kind: Service apiVersion: v1 metadata: name: my-service spec: type: ClusterIP ipFamilies: - IPv6 - IPv4 ports: - port: 80 selector: foo: bar or kind: Service apiVersion: v1 metadata: name: my-service spec: type: ClusterIP clusterIPs: - 172.30.0.99 - fd02::9999 ports: - port: 80 selector: foo: bar This turned out to have some tricky and possibly unfixable broken edge cases, so in 1.23 / 4.10, you MUST explicitly specify either "ipFamilyPolicy: PreferDualStack" or "ipFamilyPolicy: RequireDualStack" for the service to be valid. (This was fallout from a MASSIVE rewrite of the apiserver Service-handling code, https://github.com/kubernetes/kubernetes/pull/96684.) It is hard to say whether any users are actually creating services in this way. Although this behavior was described in the KEP, it never appeared in the official documentation, which always implied that you had to explicitly provide an `ipFamilyPolicy` value (https://github.com/kubernetes/website/blob/release-1.22/content/en/docs/concepts/services-networking/dual-stack.md#services). (It doesn't actually say "you MUST specify ipFamilyPolicy", but it never suggests that it's possible to omit it, and doesn't describe what would happen if you did.) If we are really concerned about this as an API break, then we could add a mutating web hook to fix things, but presumably we'd have to maintain it forever. A simpler fix might be to just modify 4.8 and 4.9 to warn loudly if the user tries to create such a service? We also need to release-note this, and should explicitly mention it to known large dual-stack-using customers.