Google App Engine - what about existing applications?

Recently, Google announced Google App Engine, another announcement in the rapidly growing world of cloud computing. This brings up some very serious questions:

1. If we want to take advantage of one of the clouds, are we doomed to be locked-in for life?
2. Must we re-write our existing applications to use the cloud?
3. Do we need to learn a brand new technology or language for the cloud?

This post presents a pattern that will enable us to abstract our application code from the underlying cloud provider infrastructure. This will enable us to easily migrate our EXISTING applications to cloud based environment thus avoiding the need for a complete re-write.