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.