Server with `--node-ip=w.x.y.z,foo:bar::baz` specified gets replaced with just the IPv4 address

[Kai Sforza]

Summary

Joining a node with both an IPv6 and IPv4 address specified in the kubeletExtraArgs."--node-ip" removes the IPv6 address.

What Should Happen Instead?

--node-ip should remain both addresses.

Reproduction Steps

1. Create two nodes with IPv4 and IPv6 addresses
2. Run the following:

   # cat << EOF | sudo tee /etc/microk8s.yaml >/dev/null
   extraKubeletArgs:
     "--node-ip": "$(ip -json a s | jq -rj '[.[].addr_info.[] | select(.scope == "global").local][0:2] | join(",")')"
   extraCNIEnv:
     IPv4_SUPPORT: true
     IPv6_CLUSTER_CIDR: fd03::/64
     IPv6_SERVICE_CIDR: fd99::/108
     IPv6_SUPPORT: true
   EOF

3. Install microk8s on both machines.
4. Verify both machines can ping each other over both IPv4 and IPv6.
5. Run grep node-ip /var/snap/microk8s/current/args/kubelet on each machine, note the two addresses on each node there.
6. Run microk8s add-node on the first machine and paste the command with the IPv4 address (IPv6 addresses won't work, see #4614) into the second machine.
7. Re-run grep node-ip /var/snap/microk8s/current/args/kubelet on each machine. Note that the first still has both IPs, but the second only has the IPv4 address.

Can you suggest a fix?

Probably just something to do with update_kubelet_node_ip in the join command.