AppDrop and portable cloud computing

The nugget in the AppDrop is that a higher-level cloud computing API (AppEngine) can be emulated on top of a lower-level cloud computing API (EC2). AppDrop achieves this with very little effort by just running Google's local-machine test environment for AppEngine on EC2.

Unfortunately, it punts on the most interesting part of AppEngine, which is scalability, especially of the data store. Although many of the blog comments say "it shouldn't be too hard to get this to run over MySQL" or even propose using HBase, I don't think anyone has done this yet.

Part of the problem might have been that running small Python apps written against a Google API was just not that compelling that companies would want to do it on multiple providers. Google App Engine has gotten much more interesting recently, however, by supporting Java. It does this through standard J2EE APIs, meaning that one can actually envision taking a serious J2EE app now and running it on AppEngine, EC2, etc. Existing J2EE storage layers are more scalable than the little AppEngine test environment used in AppDrop, so one could imagine running these apps scalably on EC2 or private clouds. However, there will still be a serious problem of sharing data across clouds.