I have a Debian based machine with 2 completely different network interfaces from 2 different ISPs acting as a backup for my server connection. These have two different IPs (Let's say IP1 and IP2backup)
I have configured the same exact port forwarding rules on both routers (Checkpoints) so both networks always point to the same host when accessing them using a specific port.
I want to make sure that when someone from the outside tries to connect to my server using my DNS, he will always be routed using IP1, unless it fails, in which case he should be directed to IP2backup.
This way I will have a back up network that can also route the required ports.
What would be the best approach to achieve this? a smart DNS? a setting in the Checkpoint router?
I have no idea and couldn't find a clear answer online.