This may be a silly question, but seeing as transfers between EC2 and S3 are free as long as within the same region, why isn't it possible to stream all transfers to and from S3 through EC2 and make the transfers completely free?
Specifically, I'm looking at Heroku, which is a Ruby on Rails hosting service run on EC2, where bandwidth is free. They already address uploads, and specifically note these are free to S3 if streamed through Heroku. However, I was wondering why the same trick wouldn't work in reverse, such that any files requested are streamed through the EC2?
If it is possible, would it be difficult to setup? I can't seem to find any discussion of this concept on Google.