Craft hosted on Google App Engine - failing to load Craft classes? Have tried getting Craft working on Google App Engine (GAE) using the GAE SDK and after defining CRAFT_STORAGE_PATH first up in the index.php, setting it to a Google Cloud Storage path eg. gs://craft-gae-storage/ I found I had to uncomment the workings of craft_ensureFolderIsReadable function in bootstrap.php so it didn't fail on the folder checks, but then it still dies with the error:

Fatal error: Class 'Craft\PhpMessageSource' not found in /Users/.../Craft-gae-HappyLager/craft/app/framework/YiiBase.php on line 213

I'm using the HappyLager demo combined with the Yii GAE codebase from https://github.com/poul-kg/yii-app-engine with a slightly modified base setup to try to get craft working:
https://github.com/moldedjelly/craft-gae
I got the same error and started debugging with XDebug.

I've put some hours in this and my conclusion is: You can't run Craft on GAE. It gets worse: You can't even run Yii1 (the framework Craft was built on) on GAE. So that's where it stops.

I did manage to get Craft running on a GAE development server instance, but to do that I had to uncomment every filesystem check in both Craft and Yii (functions like is_dir(), etc). These functions don't even work with the gs:// wrapper.