Question

A CloudOps engineer manages an Auto Scaling group of 12 EC2 instances defined in a CloudFormation template. When a new launch configuration with an updated AMI is deployed, the team requires that no more than 3 instances be replaced at a time, that each batch wait for a success signal from the application before continuing, and that the deployment roll back automatically if any batch fails. Which CloudFormation configuration meets these requirements?

Accepted Answer

Add an UpdatePolicy with AutoScalingRollingUpdate specifying MaxBatchSize of 3, MinSuccessfulInstancesPercent, and WaitOnResourceSignals with a PauseTime, and have instances send cfn-signal on successful startup.

Answer

Add a CreationPolicy with ResourceSignal to the Auto Scaling group so that each new instance signals completion during the update.

Answer

Add an UpdatePolicy with AutoScalingReplacingUpdate set to WillReplace true so the entire group is replaced behind a new group only after all instances are healthy.

Answer

Configure a DeletionPolicy of Snapshot on the Auto Scaling group and use a stack policy to limit the number of instances updated per change set.