Elastic Beanstalk (EB) is a powerful tool for deploying Rails applications on AWS, providing ease and flexibility without managing the complexities of infrastructure. A common requirement during deployment is managing background jobs efficiently. Rails developers often use the `delayed_job` gem for background job processing due to its simplicity and ease of integration. However, deploying updated code might mean restarting the jobs to ensure everything functions as expected. This article explores how to automatically restart `delayed_job` when deploying a Rails project on Amazon Elastic Beanstalk.

Understanding `delayed_job`

`delayed_job` is a robust and persistent background job processing gem for Ruby on Rails. It uses the `ActiveRecord` database to manage job queues and retries failed jobs. When a new version of your Rails application is deployed, the existing jobs need to be restarted to load the new code. This ensures that jobs use the most recent codebase and dependencies.

Automated Restart using `.ebextensions`

Adding a configuration to automatically restart `delayed_job` during a deployment can be achieved through `.ebextensions`. These are configuration files written in YAML or JSON format that automate the setup of your environment.

Creating a `.ebextensions` Configuration

1. Create a Configuration File:
   Create a directory within your Rails application root named `.ebextensions` if it doesn't already exist. Inside this directory, create a new YAML file, for example, `01_delayed_job.config`.
2. Add the Restart Command:
   In your `01_delayed_job.config`, you add commands to stop and start `delayed_job` during deployment. Example content:
   • `. /opt/elasticbeanstalk/support/envvars`: Loads environment variables set by Amazon EB.
   • `cd /var/app/current`: Navigates to the current application directory.
   • `bundle exec bin/delayed_job restart`: Executes the restart command for `delayed_job`.

• Monitor Logs or Console:
  • Use the Elastic Beanstalk console to view activity logs.
  • Check for the output confirming the restart of `delayed_job`.
• Run `delayed_job` Status Command:
  • Log in to your EC2 instance using SSH.
  • Execute `bundle exec bin/delayed_job status` to verify that the jobs are running correctly post-deployment.
• Job Queue Length:
  • Monitor the queue length to ensure jobs are being processed timely. This can be done manually or automated via monitoring tools.
• Logging and Monitoring:
  • Ensure `delayed_job` logs are being captured. These can provide insights into failures or issues during job processing.
• Scalability:
  • Elastic Beanstalk environments can be scaled horizontally. Ensure that each instance is configured to run `delayed_job` to handle increased loads effectively.
• Environment Variables:
  • Properly configure environment variables necessary for your application to ensure that `delayed_job` restarts with the needed configurations.