This is not a difficult problem. I recently had to stand up a cluster of EC2 instances for a job that required a cluster of them and used these three steps:

1. Write a script to configure an instance and run it when the instance starts.

2. Clone the instance to an image

3. Run instances based on the image.

It's quite straightforward to do. See http://github.com/gyepisam/fcc-textify for more details.