This question suggests you're just starting out, so I'd advise before trying to build anything to first familiarize yourself with the
documentation to understand how App Engine works. App Engine
does not have a single instance with a static IP address, and you
cannot listen on a socket in App Engine, only connect to outbound sockets. All inbound traffic to App Engine is HTTP(S) traffic which is directed through a front-end (
appspot.com or via your own custom domain name).