We have a server on our network that is public facing. We have Comcast cable and ATT fiber running into the building and a firewall that can handle both. I'd like to set something up that if a client goes to (mysite).com and the cable modem is down (the "primary" service) it would failover to the fiber connection to the server automatically and switch back when the cable came back up, so the server is always the same server and the client is always using www.(mysite).com, just how they get in would change depending on if a service provider is down.
What are my least expensive options for that?