I don’t know how to configure the EC2 stack, BUT…
It has been said quite multiple times here in the forum in various threads about cluster configuration, that, if you configure cache-stack AND cache-config-file, the former will take higher precedence over the latter and your custom file will be ignored. So, if you want to use one of the built-in stacks, use cache-stack, if you want to use a custom stack with a xml file, specify it with cache-config-file.