On , I learnt ...

AWS ASGs have an ‘instance refresh’ feature

Which lets you replace all the instances in an auto-scaling group, possibly with a new AMI. See the announcement from the AWS Compute Blog.

If you use an immutable infrastructure approach and deploy using AMIs, this provides an alternative deployment mechanism. In contrast to using Terraform’s create_before_destroy mechanism, which creates a new auto-scaling group for each deploy, this method would allow a single long-lived ASG to be used.

Looks interesting.