Bundler is the tool used to manager Ruby dependencies. It can be configured by several ways, through the edition of the .bundle/config file in your application project or through the environment. It is recommended not to check in the .bundle/config file in your GIT repository and keep this file to configure your development setup. The best practice here is to configure Bundler through environment variables.

Dependencies Installation

During the deployment of a Ruby application, the following command is run:

bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin

Most options of the bundle install command are configurable through environment variables starting with BUNDLE_. For instance, if you have a dependency group ci, and you want to exclude it from the production deployment you can define:

$ scalingo env-set BUNDLE_WITHOUT=development:test:ci

Gem Source protected by User and Password

If you need to install a gem which is in a repository requiring authentication:

gem "custom-gem", source: "https://gems.acmecorp.com"

You can inject the authentication thanks to the following environment variable:

$ scalingo env-set BUNDLE_GEMS__ACMECORP__COM=username:password

Then, Bundler will automatically use these credentials. It is recommended to try the configuration locally before deploying, as if it fails locally, it will fail on Scalingo:

## Example: BUNDLE_SUBDOMAIN__DOMAIN__TLD=user:password

$ BUNDLE_GEMS__ACMECORP__COM=username:password bundle install

Gem Build Configuration

Some gems can get optional flags when they are installed. It’s especially common for gems built from C code, which can receive compilation option flags, for instance with the gem sassc

gem install sassc -- --disable-march-tune-native

If you want to use these flags when the gem is installed with Bundler, you need to define the following environment variable:

## Example: BUNDLE_BUILD__<GEM>=<options>

$ scalingo env-set BUNDLE_BUILD__SASSC=--disable-march-tune-native

Once the variable is setup, it will automatically be used by Bundler when bundle install used.