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Ruby Buildpack Reference

This reference documentation offers an in-depth description of the behavior and configuration options of the Paketo Ruby Buildpack. For explanations of how to use the buildpack for several common use-cases, see the Paketo Ruby Buildpack How To documentation.

Supported Dependencies

The Ruby Paketo Buildpack supports several versions of MRI, Bundler, and common Ruby webservers and task runners. For more details on the specific versions supported in a given buildpack version, see the release notes.

Package Management

The Ruby Buildpack uses Bundler to install and manage the gems needed to run your application. Including a Gemfile in your app source code instructs the bundle-install buildpack to vendor your dependencies using bundle install.

Webservers & Task Runners

The Ruby Buildpack supports a number of webservers and task runners that are useful for running Ruby applications. If your application uses one of these tools, it will be automatically detected and a start command for your application will be assigned when building your application container.


Task Runners

Rails Asset Pipeline

The Paketo Rails Assets Buildpack is a component buildpack included in the Ruby Buildpack. It supports Rails apps (Rails version >= 5.0) that need asset precompilation.

The buildpack runs bundle exec rails assets:precompile for the app, and works with any of the supported Ruby webservers listed above.

Buildpack-Set Environment Variables

The Ruby CNB sets a few environment variables during the build and launch phases of the app lifecycle. The sections below describe each environment variable and its impact on your app.


  • Set by: mri, bundler
  • Phases: build and launch
  • Value: location of the directory gems will be installed for each respective dependency


  • Set by: bundle-install
  • Phases: build and launch
  • Value: location where all gems in your bundle will be located

Last modified: October 13, 2021