Update : Puma 7.0 was released with a fix for the bug described in this article. We recommend Ruby applications upgrade to Puma 7.0.4 or higher. This week , Heroku made Router 2.0 generally available, bringing features like HTTP/2 , performance improvements and reliability enhancements out of the beta program ! Throughout the Router 2.0 beta, our engineering team has addressed several bugs, all fairly straight-forward with one exception involving Puma -based applications. A small subset of Puma applications would experience increased response times upon enabling the Router 2.0 flag, reflected in customers’ Heroku dashboards and router logs. After thorough router investigation and peeling back Puma’s server code, we realized what we had stumbled upon was not actually a Router 2.0 performance issue. The root cause was a bug in Puma! This blog takes a deep dive into that investigation, including some tips for avoiding the bug on the Heroku platform while a fix in Puma is being developed.…