My apps on Heroku have been cruising along ok using Thin as my rack server, but on my VPS boxes, Unicorn. I was hoping to keep a more consistent experience for myself and as it turns out, getting my Heroku apps to run on Unicorn is pretty simple and runs really fast.

1st: I added a Unicorn config file: touch config/unicorn.rb and added the following:
worker_processes 3 timeout 30 preload_app true

2nd: I added Unicorn to my GemFile:
#rack server gem 'unicorn' You will want to “bundle install” after that step so that it gets picked up and added to your Gemfile.lock

3rd: I added a Procfile to the root of my app: touch Procfile and added the following:
web: bundle exec unicorn -p $PORT -c ./config/unicorn.rb

Commit it into Git, then git push heroku branchname and you are enjoying the sweet sweet threading love of Unicorn.