Accessing Arduino Yun from Internet
Well, I'm not familiar with the Yun, but the first thing that stands out is the missing

Bridge.begin();


line apparently needed to initialize the Bridge library that you use.

And you do have something like

YunClient client = server.accept();


and "more" in the main loop (or a function where applicable) of your code, right ?

And yes, noListenOnLocalhost() is the correct function for serving external clients.