You recently encountered a major bug in your web application during a deployment cycle. During this failed deployment, it took the team four hours to roll back to a previously working state, which left customers with a poor user experience. During the post-mortem, you team discussed the need to provide a quicker, more robust way to roll back failed deployments. You currently run your web application on Amazon EC2 and use Elastic Load Balancing for your load balancing needs.

Answer options:

A.Create deployable versioned bundles of your application. Store the bundle on Amazon S3. Re-deploy your web application on Elastic Beanstalk and enable the Elastic Beanstalk auto – rollback feature tied to CloudWatch metrics that define failure.
B.Use an AWS OpsWorks stack to re-deploy your web application and use AWS OpsWorks DeploymentCommand to initiate a rollback during failures.
C.Create deployable versioned bundles of your application. Store the bundle on Amazon S3. Use an AWS OpsWorks stack to redeploy your web application and use AWS OpsWorks application versioning to initiate a rollback during failures.
D.Using Elastic BeanStalk redeploy your web application and use the Elastic BeanStalk API to trigger a FailedDeployment API call to initiate a rollback to the previous version.

Answer – B
The AWS Documentation mentions the following
AWS DeploymentCommand has a rollback option in it. Following commands are available for apps to use:
deploy: Deploy App. 
Ruby on Rails apps have an optional args parameter named migrate. Set Args to {"migrate":["true"]} to migrate the database.
The default setting is {"migrate":["false"]}.
The "rollback" feature Rolls the app back to the previous version. 
When we are updating an app, AWS OpsWorks stores the previous versions, maximum of upto five versions. 
We can use this command to roll an app back as many as four versions.
Reference Link: 
http://docs.aws.amazon.com/opsworks/latest/APIReference/API_DeploymentCommand.html