I've an m4.4xlarge instance running Percona MySQL 5.7 on Ubuntu 16.04 and I plan to change the instance family to m5a.4xlarge. Are there any unforeseen problems that I might run into when doing this or is it just a matter of shutting down the instance, changing the instance type and restarting it again? Are there any linux kernel level compatibility issues that I need to look into?
The only potential data issue would be if you used instance store (as opposed to Elastic Block Storage) for the disk, but that's unlikely. Also, the IP address of the instance will change, so any applications that depend on that IP will need to be configured with the new IP. And as @ceejayoz pointed out, it's easy enough to test!