When I worked in adtech (Brightroll) we hosted a segment mapping server on heroku. All it did was look at a url query for the target url, append a value from a cookie to it, and 302 to that url. The value in adtech is that I can tell you which segment a user is in by taking the data in my cookie and appending it to your url.

We launched it on Heroku using Nodejs and sent billions of requests a day to it. The thing ran on like a few dozen dynos, but it was responsible for like 20-30% of all of Heroku's bandwidth. Fantastic value for us. Immediate headache for Heroku.