Well, I knew that the public DNS would not persists through a stop/start of an EC2 instance, easy enough to get around, use an Elastic IP. I do most of my AWS work inside of a VPC, I had to step outside of that for a project setting up a web app & sql server, I used the private IP of the EC2 instance, not thinking I would need to change the instance type (small -> medium) but when I did…. 🙂 no db connectivity on app server.
I do most of my work inside a VPC, my advice is to launch your instances inside a VPC, I never have figured out why I cannot change the size of an EC2 instance with a simple restart though.. thereby preserving my DNS settings.
Better still, use Route53 to setup a CNAME, point that to the internal IP of the instance and voila, still avoid the bandwidth usage and no need to modify connection strings.