Q: When I create my Matrix application, why is Matrix telling me “This port is already used by another application”?
A: Each Matrix Server can forward a port to exactly one application. A server cannot forward the same port to two different applications. Since a Matrix Server can handle multiple applications, any new application will automatically be checked against existing ports to avoid conflicts.
Q: If such a conflict occurs, how do I address it?
A: The primary way to address this is to create a separate Matrix server. With a separate server, Matrix will be able to route the traffic for two different apps to the same port.
Q: What about port forwarding in this case?
A: Port forwarding is designed as an ease-of-use feature, where the user is accessing a default port like 443, even though the app may be listening on something like 8443. It will not fix routing issues, but if you could reconfigure the target app to use a non-standard port, port forwarding might be used to ease access to the two apps. However, you still can only forward one port on the same Matrix server. You cannot forward Port 80 to one app port 123, and then on the same server forward Port 80 to 456.