How should I organize multiple Express servers on the same system?

I’m using one server to host multiple Node.js web apps, which are distributed across multiple domains. My current practice is to run an Express server for each app on a different port, and to run a base server that simply routes (redirects) requests to the correct port/Express server. This works, but it means that my base server is routing every single HTTP request (and by manually redirecting it), and that my users see my apps as hosted at []:8000.