Memory Leak

Problem

We've been experiencing a memory leak in our node servers. Over the course of a day or so the memory in our servers started to fill until we got an alert and had to restart the app. We added new relic to check the node VM memory: Upon debugging and testing we've come to the conclusion that the leak could be in express. We did some test on a clean express server, printing the heap before and after a lot of request and we see the memory increasing but never going back to the initial value. We tested on various versions of Node and two versions of express (4.16.2 and 4.14.1) and we had the same results. I'll add the last test setup so you can reproduce it. Tested on OSX 10.12.6 Node 7.6.0 Express 4.16.1 Code [code block] run with `node --expose-gc server.js` autocannon command `autocannon -a100000 -c5 http://localhost:9000/` Results: <img width="745" alt="screen shot 2018-02-05 at 17 54 44" src="https://user-images.githubusercontent.com/1228656/35828372-01003654-0a9e-11e8-95ca-899450cf9f20.png"> This is just one of the many test we made, all with similar results