One Linux host, 2 network interfaces, 2 separate http server app each using a NIC

I have two server applications that I want to run on one machine, but I want the two embedded http servers to respond
to request from separate network interfaces. One network interface is connect to the internet, the other interface connects
to a preprogrammed router with embedded VPN client--I have no control over this router.

One server application will be accessed from internet with http requests using https protocol, as well as setup secure websockets using wss protocol
to IoT nodes.

The other server application will operate similarly (https/wss thru http server) but will be reached through connection over VPN tunnel.

OS is Ubunty 18.04, http server is Restinio (C++).

Assuming the two server applications are the same design, is it as simple as configuring each http server address to a subnet address from
their respective NIC interfaces?

What else should I know to configure to make this work well?

Thanks