The solution is fairly simple in principle. You need to have fallback IPs in your clients, that they can connect to in case DNS fails.

But that also means you need to have IPs that will last for as long as your client lasts. Which means you need to have a defined lifetime for your client. And you need to have some mechanism to validate the IPs are still your servers and not been taken over by someone else (mutual authentication).

> But that also means you need to have IPs that will last for as long as your client lasts.

It sounds like implementing this scheme without a method to rotate IP addresses would be a mistake. But maybe I'm missing something.

You could store fresher IPs after succesful connection. But that doesn't help for people who install from an older (but not expired) installer, while they're on a network with bad DNS.

First thing that occurred to me was WebRTC for P2P chat using an IP address in the STUN fallback list if DNS fails? As in https://github.com/michal-wrzosek/p2p-chat