You can customize deployment by implementing a custom recipe to perform the required tasks and assigning it to the appropriate layer's Deploy event. An alternative and sometimes simpler approach—especially if you don't need to implement a cookbook for other purposes—is to use Chef deployment hooks to run your customization code. In addition, custom Deploy recipes run after the deployment has already been performed by the built-in recipes. Deployment hooks allow you to interact during a deployment, for example, after the app's code is checked out of the repository but before Apache is restarted.
Chef deploys apps in four stages:
Checkout–Downloads the files from the repository
Migrate–Runs a migration, as required
Restart–Restarts the application
Chef deployment hooks provide a simple way to customize a deployment by optionally
running a user-supplied Ruby application after each stage completes. To use deployment
hooks, implement one or more Ruby applications and place them in your app's
/deploy directory. The application must have one of the
following names, which determines when it runs.
before_migrate.rb runs after the Checkout stage is complete but
before_symlink.rb runs after the Migrate stage is complete but
before_restart.rb runs after the Symlink stage is complete but
after_restart.rb runs after the Restart stage is complete.
Chef deployment hooks can access the node object by using standard node syntax, just
like recipes. Deployment hooks can also access the values of any app environment variables
that you have specified. However, you must use
new_resource.environment[" to access the variable's value instead of
ENV[". For more
information, see deploy.
For more information on how to use deployment hooks and what information a hook can access, see Deploy Phases.