Comments federate to instances with subscribed users for that community. The first time a user subscribes to the community federation will start and future comments will begin to show up on the instance. Can’t see old comments… on smaller/self instances that problem will be more visible.
Running a reverse proxy then adding your IP to your router/other-DNS-server will make it easy ish. Just don’t pick a domain that is used by other people. If you have a(ny) domain you own then a subdomain you set in your router is fine/safe.
I have *.[house domain] point to a static IP set in my router. The IP is announced via BGP to point to running Traefik instances as a reverse proxy that points to the appropriate container. This also gives certs, but isn’t required.
This sounds about half of the way to Nostr. User identity is separate from posting. Communities (relays) host the content and can have the own policies for who can interact.