Baby steps with EngineYard

admin wrote this on 26 Sep 2012

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So the much awaited moment has come : the time to roll up my sleeves and get my hands dirty and deploy the Rails App onto the EngineYard stack .

As I stand at square one and look above with awe at the very sensitive and very crucial deployment , I shift my attention to the top right corner of my monitor where the clock’s minute digit just moved one step closer into the friday night , I feel humbled by the volume of stackoverflow questions that will be passing in front of my eyes tonight . Even though I’m fighting time , I realize I need the basics .

So how does EngineYard work ? What is an Engine Yard deployment ? Engine Yard docs are a blessing . Here are the steps of a deployment that goes on behind the scenes , for your reading pleasure :

1. Code fetch

• On the application master, the source code is fetched from the git repository, then the chosen branch is checked out into /data/<appname>/shared/cached-copy. The application master then copies this (via rsync) to all the other instances in your environment.
• On each instance, the contents of /data/<appname>/shared/cached-copy are copied to /data/<appname>/releases/<timestamp>.

2. Gem bundling

After your code is copied to all instances in your environment, the server-side component checks for the existence of a Gemfile.

• If a Gemfile is found, the bundler gem is installed and the command bundle install is run on each application instance.
• If you need a specific version of bundler, specify it in your Gemfile.
• We suggest you generate a Gemfile.lock to ensure consistency across deployment environments.

3. Default configuration

After your application gems are installed, the server-side component
generates and symlinks configuration files and directories for your
application.

• Configuration files and directories necessary for your application
  are generated or symlinked and put into place. Examples of these files
  include: config/database.yml, config/mongrel_cluster.yml, config/newrelic.yml, the log directory and more.

4. Database migration

After default configuration has been setup, your database migrations are run with appropriate deploy hooks.

• The deploy hook deploy/before_migrate.rb is run.
• The migration command specific to your application is run (see the --migrate option).
• Finally, the deploy hook deploy/after_migrate.rb is run.

5. Application Symlink

After migrations and their deploy hooks have been executed, your application symlink is created.

• The deploy hook deploy/before_symlink.rb is run.
• Your application symlink is created.
  /data/<appname>/current points to /data/<appname>/releases/<timestamp>
• Finally, the deploy hook deploy/after_symlink.rb is run.

6. Restart application servers

After your application code is in place and has been appropriately symlinked, restart your application servers.

• The deploy hook deploy/before_restart.rb is run.
• Your application servers in your environment are now restarted. For
  example, if your environment is using Passenger, the server-side
  component will touch the file /data/<appname>/current/tmp/restart.txt to tell Passenger to restart.
• Finally, the deploy hook deploy/after_restart.rb is run.

7. Final cleanup

If there are more than three previous releases in /data/<appname>/releases, all but the most recent three are removed. Your deployment is now finished.

 

Contributor : Emil Soman

References :

• https://support.cloud.engineyard.com/entries/20996711-how-your-code-is-deployed-on-engine-yard-cloud

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Tags: Cloud, EngineYard, ruby, RubyOnRails