The systems are dual stack, not IPv6-only. If I add the v6 address as well, won't it create confusion in the cluster communication and other things?
On the other hand, the HNs use dynamic v6 addresses via SLAAC. This is a technical limitation in that system. So I can't just add an address because it will change over time. The daemon would need to listen on the wildcard v6 address as it does with v4. Usually it's accomplished by opening a listening socket on the wildcard v6 address ( :: ) and that will automatically open the v4 listening socket on the wildcard v4 address (0.0.0.0) as well. If that's not possible (eg. an exception is thrown or some other error is observed) the daemon should fall back to v4 only. So in fact it's very simple, I don't understand why it hasn't been implemented that way.