This article was originally authored by Srinath Ananthakrishnan, an engineer on the Heroku Runtime Networking Team

Summary

This following story outlines a recent issue we saw with migrating one of our internal systems over to a new EC2 substrate and in the process breaking one of our customer’s use cases. We also outline how we went about discovering the root of the issue, how we fixed it, and how we enjoyed solving a complex problem that helped keep the Heroku customer experience as simple and straightforward as possible!

History

Heroku has been leveraging AWS and EC2 since the very early days. All these years, the Common Runtime has been running on EC2 Classic and while there have always been talks about moving to the more performant and feature rich VPC architecture that AWS offers, we hadn’t had the time and personnel investment to make it a reality until very recently.…