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Ruby Buildpack

The Paketo Ruby Buildpack supports several popular configurations for Ruby apps.

To build a sample app locally with this buildpack using the pack CLI, run

git clone <https://github.com/paketo-buildpacks/samples>
cd samples/ruby/puma
pack build my-app --buildpack gcr.io/paketo-buildpacks/ruby \
  --builder paketobuildpacks/builder:base
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See samples for how to run the app.

NOTE: Though the example above uses the Paketo Base builder, this buildpack is also compatible with the Paketo Full builder.

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.

Specifying a Ruby Version

The Ruby Buildpack allows you to specify a version of Ruby to use during deployment. This version can be specified via the BP_MRI_VERSION environment variable or a Gemfile. When specifying a version of Ruby, you must choose a version that is available within the buildpack. The supported versions can be found here.

Please note that setting the Ruby version through a buildpack.yml file will be deprecated in MRI Buildpack v1.0.0.

The buildpack prioritizes the versions specified in each possible configuration location with the following precedence, from highest to lowest: BP_MRI_VERSION, Gemfile.

Specifying a version of Ruby is not required. In the case that is not specified, the buildpack will provide the default version, which can be seen in the buildpack.toml file.

Using BP_MRI_VERSION

To configure the buildpack to use Ruby v2.7.1 when deploying your app, set the following environment variable at build time, either directly (ex. pack build my-app --env BP_MRI_VERSION=2.7.1) or through a project.toml file:

BP_MRI_VERSION="2.7.1"
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Using a Gemfile

To configure the buildpack to use Ruby v2.7.1 when deploying your app, include the values below in your Gemfile:

source 'https://rubygems.org'

ruby '~> 2.7.1'
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Deprecated: Using buildpack.yml

Specifying the Ruby version through buildpack.yml configuration will be deprecated in MRI Buildpack v1.0.0. To migrate from using buildpack.yml please set the $BP_MRI_VERSION environment variable.

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.

Specifying a Bundler Version

The Ruby Buildpack allows you to specify a version of Bundler to use during deployment. This version can be specified via the BP_BUNDLER_VERSION environment variable or a Gemfile.lock created during dependency vendoring. When specifying a version of Bundler, you must choose a version that is available within the buildpack. The supported versions can be found here.

Please note that setting the Bundler version through a buildpack.yml file will be deprecated in Bundler Buildpack v1.0.0.

The buildpack prioritizes the versions specified in each possible configuration location with the following precedence, from highest to lowest: BP_BUNDLER_VERSION, Gemfile.lock.

Specifying a version of Bundler is not required. In the case that is not specified, the buildpack will provide the default version, which can be seen in the buildpack.toml file.

Using BP_BUNDLER_VERSION

To configure the buildpack to use Bundler v2.1.4 when deploying your app, set the following environment variable at build time, either directly (ex. pack build my-app --env BP_BUNDLER_VERSION=2.1.4) or through a project.toml file:

BP_BUNDLER_VERSION="2.1.4"
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Using a Gemfile.lock

To configure the buildpack to use Bundler v2.1.4 when deploying your app, run bundle install on your application source code using v2.1.4 of Bundler. This will result in a Gemfile.lock that includes the following snippet:

BUNDLED WITH
   2.1.4
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Deprecated: Using buildpack.yml

Specifying the Bundler version through buildpack.yml configuration will be deprecated in Bundler Buildpack v1.0.0. To migrate from using buildpack.yml please set the $BP_BUNDLER_VERSION environment variable.

Vendored Packages

In order to build apps in an offline environment, the app will need to have the .gem files located in the cache_path. Bundler will copy the required gems into this location, typically vendor/cache when running the bundle package command. During the bundle install process, the buildpack will instruct Bundler to prefer gems in this cache over those on the RubyGems index by running bundle install --local.

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 applicatin will be assigned when building your application container.

Webservers

• Passenger
• Puma
• Rackup
• Thin
• Unicorn

Task Runners

• Rake

Rails Asset Pipeline

The Rails Assets buildpack supports Rails apps (Rails version >= 5.0) that need asset precompilation.

To use this buildpack, your app must contain an app/assets directory, and your app’s Gemfile must specify the rails gem. 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.

GEM_PATH

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

BUNDLE_PATH

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

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