Using Puma on Heroku instead of Unicorn

A few years back I wrote about using Unicorn on Heroku along with Unicorn Worker Killer. Oyr need was to increase the number of web requests an app could handle on Heroku. Puma tested faster at the time but did not offer worker processes. You have to use threads and for an app that was never intended to be threaded running on Ruby MRI it was too much work to adjust. Puma has since added the concept of Worker Processes and, given the performance advantages found with Puma it made sense to install it. Still, I was used to some variability with Unicorn and wanted to replicate some of the same things. This article from Heroku offered most of the help I needed though I did reduce the default thread count from 5 to 1. Additionally the section on the use of the Rack Timeout gem was helpful though I wound up doing this so that I could adjust the timeout via environment variable:

 Rack::Timeout.timeout = 20 # seconds  

What I did not find was helpful instructions on queue length. Puma defaults to 1024 and the previously mentioned article from Heroku cautions strongly against altering that queue length. Still, from previous performance testing on Heroku sometimes a shorter queue length is warranted (DO YOUR OWN TESTING!). This blog post originally suggested altering the queue length but again he cautions against it on Heroku. If you find that a shorter queue length helps then it is a setting in the config/puma.rb file:

 backlog = Integer(ENV['PUMA_BACKLOG'] || 20)  
 bind "tcp://0.0.0.0:#{port}?backlog=#{backlog}"   

Good luck and Heroku on