Question

A DevOps team deploys an application using a CloudFormation nested stack architecture. One nested stack provisions an Auto Scaling group of EC2 instances that run a lengthy bootstrap process via cfn-init before the application is ready. During recent stack updates, the parent stack update repeatedly succeeds and reports UPDATE_COMPLETE even though several instances fail to finish their bootstrap and never become healthy, causing the application to serve errors after the deployment. The team wants CloudFormation to treat the update as failed and roll back automatically when instances do not complete initialization. Which change to the EC2 nested stack template will achieve this?

Accepted Answer

Add a CreationPolicy with a ResourceSignal count and timeout to the Auto Scaling group, and have the bootstrap script call cfn-signal reporting success or failure; also configure an UpdatePolicy with WaitOnResourceSignals for rolling updates.

Answer

Add a DependsOn attribute from the Auto Scaling group to the launch template so the group waits until the launch template is fully created before scaling.

Answer

Enable termination protection on the nested stack and set the parent stack's OnFailure parameter to ROLLBACK.

Answer

Increase the parent stack's timeout by adding a longer TimeoutInMinutes value to the AWS::CloudFormation::Stack resource pointing to the nested stack.