Buckshot
Helps to switch between shotgun and thin appropriately. Can be used inside your Procfile to allow you to use shotgun easily for development.
Usage
# Gemfile
gem "buckshot"
# Procfile
web bundle exec buckshot
Details
Will use the appropriate webserver for your environment.
$ RACK_ENV=development PORT=4000 buckshot
# shotgun -p 4000 -E development
$ RACK_ENV=production PORT=4000 buckshot
# thin start -p 4000 -e production