Declare App Dependencies

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Cloud Foundry recognizes an app as a Ruby app by the existence of a Gemfile and a Gemfile.lock file in the root directory.

The demo app you deployed already has a Gemfile, and it looks something like this:

source 'https://rubygems.org'

gem 'puma'
gem 'rack-coffee'

group :web do
  gem 'haml'
  gem 'sinatra'
  gem 'sass'
end

group :development do
  gem 'sinatra-reloader'
end

The Gemfile file specifies the dependencies that should be installed with your application.

When an app is deployed, Cloud Foundry reads this file and installs the appropriate Ruby version together with the dependencies using the bundle install command.

Now run bundle install in your local directory to install the dependencies, preparing your system for running the app locally:

$ bundle install
Using backports 3.3.5
Using coffee-script-source 1.6.2
Using multi_json 1.7.6
Using tilt 1.4.1

...

Pro Tip: It’s good practice to specify the Ruby version to use in your Gemfile. Be aware though, that Cloud Foundry only accepts the Ruby versions specified here.

Once dependencies are installed, you will be ready to run your app locally.