Improved concurrency for Heroku Dynos

A Rack application running on heroku can improve performance by using different application servers with different performance characteristics.

Some good choices include Thin (evented I/O), Unicorn (multi-process) and Puma (multi-threaded).

The exact configuration settings will vary by application and how much memory each app takes. A default Rails app with a basic scaffold can easily support 4 unicorn workers or 4 puma threads. A small Sinatra app can support several times that number.

Here are the Procfile settings you can use for each:

# thin
web: bundle exec thin -p $PORT -e $RACK_ENV start

# puma
web: bundle exec puma -t 1:4 -b tcp://0.0.0.0:$PORT

# unicorn
web: bundle exec unicorn -p $PORT -c ./config/unicorn.rb

Use the New Relic RPM Add-on to monitor your application resources.