Only one family endpoints for dual-stack service

What kind of issue is this?

/kind bug

Expected behaviour

For a service with ipFamilyPolicy: RequireDualStack endpoints of both families should be sent to the backend (always)

Actual behaviour

I only get endpoints from one family. Which one, ipv4 or ipv6, seems a bit random.

I understand that this is a fundamental feature, without it dual-stack can't work, and all backends would fail. However, I suspect that the to-api may be the culprit. Or I have missed some updated configuration (I have been away from kpng for a while)

Steps to reproduce the problem

Use the setup from the blog post. Use the service as-is and start 2 PODs with the correct selector. I use a Deployment with "replicas: 2", but that shouldn't be important.

Output from kpng-json | jq:

{
  "Service": {
    "Namespace": "default",
    "Name": "kpng-example",
    "Type": "ClusterIP",
    "IPs": {
      "ClusterIPs": {},
      "ExternalIPs": {
        "V4": [
          "10.0.0.55"
        ],
        "V6": [
          "1000::55"
        ]
      },
      "Headless": true
    },
    "Ports": [
      {
        "Protocol": 1,
        "Port": 6000,
        "TargetPort": 6000
      }
    ],
    "SessionAffinity": null
  },
  "Endpoints": [
    {
      "IPs": {
        "V4": [
          "11.0.2.2"
        ]
      },
      "Local": true,
      "PortOverrides": [
        {
          "Port": 6000
        }
      ],
      "Scopes": {
        "Internal": true,
        "External": true
      }
    },
    {
      "IPs": {
        "V4": [
          "11.0.1.2"
        ]
      },
      "PortOverrides": [
        {
          "Port": 6000
        }
      ],
      "Scopes": {
        "Internal": true,
        "External": true
      }
    }
  ]
}

Only IPv4 endpoints are provided. But endpoins-slices for both families exist:

# kubectl get endpointslices
NAME                 ADDRESSTYPE   PORTS   ENDPOINTS             AGE
kpng-example-lq2ch   IPv6          6000    1100::102,1100::202   5m9s
kpng-example-tnhrv   IPv4          6000    11.0.1.2,11.0.2.2     5m9s
kubernetes           IPv4          6443    192.168.1.1           6m28s

kubernetes-retired / kpng