Configuring Rake Tasks for Deployed Apps

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For Cloud Foundry to automatically invoke a Rake task while a Ruby or Ruby on Rails app is deployed, you must do the following:

  • Include the Rake task in your app
  • Configure the application start command using the command attribute in the application manifest

The following is an example that shows how to invoke a Rake database migration task at application startup.

  1. Create a file with the Rake task name and the extension .rake, and store it in the lib/tasks directory of your application.

  2. Add the following code to your rake file:

    namespace :cf do
    desc "Only run on the first application instance"
    task :on_first_instance do
        instance_index = JSON.parse(ENV["VCAP_APPLICATION"])["instance_index"] rescue nil
    exit(0) unless instance_index == 0
    end
end

    This Rake task limits an idempotent command to the first instance of a deployed application.

  3. Add the task to the manifest.yml file with the command attribute, referencing the idempotent command rake db:migrate chained with a start command.

    applications:
‐ name: my-rails-app
  command: bundle exec rake cf:on_first_instance db:migrate && rails s -p $PORT