If you're hosting your application servers at Linode, use a local database server hosted at Linode. If you're hosting your application servers at Amazon, use a local database server hosted at Amazon. It's not a good idea to have your database sitting on the other side of the public Internet. For performance reasons, if nothing else. I remember a guy came by here a while ago complaining of terrible database performance, and it turned out he was running his database server on a dedicated box somewhere else and trying to connect his linodes to them.
