Two incoming internet lines per gateway. How?

Question

Computer networks

There are
- two offices, a couple of kilometers apart, interconnected by optics;
- two cables from two providers come to one remote office;
- both offices use the same subnet (eg 192.168.1.0/24);
- the ability to transfer one of the providers to another office, at a minimum cost.
Purpose
- To get rid of problems with the Internet in the event of a power outage in one of the offices (this happens once every one or two months).
It is assumed that the gateway will be in the main office, in the remote one there will be a backup.
I would like to bring both providers from different offices to one gateway, from which all clients will receive the Internet. How is it possible to implement it?

Answer 1

Do providers also turn off the equipment if there is no light in the building?
And optics is only tied to your equipment?
Well, then transfer 1 provider to the second office, so that each office has an external connection.
The routers in both offices are connected by your optics, each has an internet connection.
And configure the failover and routes as you need. There are several options, depending on whether the channels are equivalent, or one, for example, with a minimum speed as a backup.
I think this can be done on any piece of iron, but do you have optics already plugged into something?

Answer 2

Well, for example, put a Mikrotik, and balance the channels.

Answer 3

The task is not entirely clear. Do you need to bring both uplinks to one gateway and use it to natit users of two physical offices in the same subnet in these two uplinks? If so, then it is solved, if not, then explain in more detail.