I'm using MySQL for the backend.
Here is an article about setting up AWS EC2 to run Play and Mongo: http://stevenwilliamalexander.wordpress.com/2012/06/10/amazon-ec2-mongo-play-scala-instance-setup-gu/ and there are also guides for binding to Amazon Simple DB and Dynamo in Scala as well that might be much easier setup than using MySQL.
I've used a lot of AWS services for building composite services and I'm available for a call if you get stuck or need any advice on best practices.
