Ruby is entirely supported by Scalingo, furthermore, custom support is added for the Rails framework in all its versions.


The buildpack is based on bundler and will install the dependencies defined in the Gemfile and Gemfile.lock of your project. (source of the buildpack)

Ruby application

Ruby app detection

Presence of a Gemfile

Rack based application

Rack app detection

Presence of a

Rack environment

When a rack application is detected, the following environment variable will be set:

  • RACK_ENVproduction

Rails application

Rails app detection

Rails 2

Presence of a config/environment.rb

Rails 3, Rails 4

Presence of a config/application.rb

Rails 5

Presence of a config/application.rb

For Rails 5.1, node and yarn will be automatically installed if ther gem webpacker is installed

Rails environment

  • RACK_ENVproduction
  • RAILS_ENVproduction

Specifying a custom ruby runtime

If your need to install a custom version of ruby, you can achieve that by specifying it in your Gemfile:

Ruby MRI 2.4.2

ruby "2.4.2"

JRuby 2.0.0

ruby "2.0.0", :engine => "jruby", :engine_version => "1.7.20"

List of the compatible runtimes

Only last patch version of each major release is listed here, but other minor version are also present if your require them for specific tests.


  • 2.5.0
  • 2.4.2
  • 2.3.5
  • 2.2.8
  • 2.1.10
  • 2.0.0


  • 1.7.18: Ruby versions: 1.8.7, 1.9.3, 2.0.0
  • 1.7.19: Ruby versions: 1.8.7, 1.9.3, 2.0.0
  • 1.7.20: Ruby versions: 1.8.7, 1.9.3, 2.0.0
schedule 27 Oct 2017