It's a node app that tries to keep things simple, i.e. no big frameworks. I put thought into performance as well and it has seen a significant number of re-writes. I didn't just get there from nothing. The project is about 6 years old.

Edit: I should add that I ran into performance hurdles now and then, causing me to upgrade to more expensive hardware until I had resolved them. It was mostly memory leaks or inefficient IO/websockets. Nothing took longer than a week to fix so far though.