Observe an automatic rollback

Your team deploys version 2.1 of the checkout API using a blue/green deployment on EC2. The green fleet passes the ValidateService health check and CodeDeploy shifts traffic from blue to green. Two minutes later, the 5xxErrorRate CloudWatch alarm enters the ALARM state.

Automatic rollback is enabled on the deployment group with the option "Roll back when a deployment fails" and "Roll back when alarm thresholds are met."

What happens next?