The correct answer is C because for an in-place deployment on Amazon EC2 instances, AWS CodeDeploy automatic rollback works by redeploying the last known good revision when a deployment fails or when a configured monitoring alarm is triggered. AWS documentation explains that when automatic rollback is enabled, CodeDeploy creates a new deployment that uses the most recent successfully deployed application revision. This rollback deployment receives its own new deployment ID , because it is treated as a separate deployment event rather than a simple undo operation.

Option A is incorrect because CodeDeploy does not restore an Amazon S3 snapshot of the previous deployment state for EC2 in-place deployments. It redeploys the last successful revision instead. Option B describes behavior associated with blue/green deployment patterns , not in-place deployments . Route 53 alias switching and blue/green environment replacement are not how CodeDeploy handles failed validation during an EC2 in-place deployment. Option D is incorrect because CodePipeline orchestrates stages in a delivery pipeline, but it is not the service that performs the rollback behavior described here.

This distinction is important in AWS deployment design. In-place deployments update the same EC2 instances already serving the application. If validation fails, CodeDeploy does not roll traffic back through DNS or infrastructure replacement. Instead, it launches a rollback deployment of the previously successful application revision across those same instances. That behavior directly aligns with AWS CodeDeploy automatic rollback functionality for EC2/On-Premises in-place deployments.

Therefore, the correct result is that CodeDeploy redeploys the last known stable version as a new deployment , which makes C the right answer.