After the announcement of Google App Engine's Java support, JRuby was shown to work on GAE. There are limitations, though, and JRuby's Nick Sieger lists a few of the limitations; some examples are:
- No RMagick/ImageScience/attachment_fu. No ImageVoodoo even (no javax.image APIs). Google has it's own image manipulation API. [..]
- 1000-files limit per application. In order to work around this, I ended up jarring up all the Rails gems when deploying a Rails application.
Tom Enebo recently twittered about having added GAE support to image_vodoo. Nick also points to the JRuby app he deployed on GAE.
Deploying a JRuby application is not yet completely automated, but some tools are worked on right now. One is reggae, which helps to deploy Rack applications to GAE.
Finally, while JRuby largely works on GAE, some popular libraries don't; the biggest example is ActiveRecord because Google only offers its own DataStore, which is not relational.
However, another ORM is now supported on Google's DataStore: DataMapper. Genki Takiuchi created the dm-datastore-adapter, which allows to use DataStore with DataMapper. Currently, a few query options are supported with DataStore.
