I think it would be best to use the private host, port, and url for mongo, along with using template variable functions for variables like passwords.

Brody, thanks for your suggestions - I've added a variable function for the password.

New to private networking on Railway though - pointing MONGOURL to ${{MongoDB.MONGOPRIVATE_URL}} seems to work, but is that what you're suggesting? What do I need to change for the private host and port vars?