Is there any way to automatically change the instance type of an aws ec2 instance without any downtime?

Question

I want to change the instance type of an aws ec2 instance based on the cpu utilization of the instance. Basically i want the instance type to be t3.large if the cpu utilization is > 80% and t3.medium if it is below that. Is there any way to achieve this without any downtime? Can i achieve this with aws cloudformation? If so can you provide me a guide or link which i can refer to?

Answer 1

Unfortunately, you can't do this. Changing instance type requires stopping your instance:

You must stop your Amazon EBS–backed instance before you can change its instance type.

However, you could setup your instance(s) to operate in an autoscaling group. This way you could use UpdatePolicy to perform rolling or replacing update. This could be use to ensure that part or full fleet of your instances is operating while the new instance types are rolled out.