Until recently, stacks within Idealstack were limited to a single RDS instance. This was quite restrictive, and made it hard to do things like supporting multiple mysql versions or moving between them.
Now when editing stacks within Idealstack, in the Database Instances (RDS) section you can add as many database instances as you like:
Idealstack is the ideal way to run PHP on AWS. A fault tolerant, autoscaling hosting cluster, which transparently cluster-enables your sites and apps in your own AWS account, all controlled from an easy to use web control panel.