A new AMI must be rolled out to an ASG gradually, keeping 90% healthy, pausing at checkpoints, and rolling back if alarms fire. What should be used?
Show answer and explanation
Answer: A
Instance refresh replaces the group's instances with a new launch template and has native support for every part of the requirement: MinimumHealthyPercentage 90 keeps the floor, checkpoints pause the rollout at set percentages for a wait time, and auto rollback reverts to the previous template when the configured CloudWatch alarms fire during the refresh.
Why the other options are wrong
- B. Terminating instances by hand may get the new AMI out eventually, but everything — the 90% floor, the pauses, the rollback — depends on a human watching; one incident during the night and it fails.
- C. A new ASG plus a traffic swap is a workable blue/green style approach, but it's fully custom: the group, the cutover, the health floor, and the rollback are all scripted and operated by you.
- D. CodeDeploy in-place updates an application on existing instances; it isn't the mechanism for gradually swapping an Auto Scaling group over to a new AMI with checkpoints.