The setup worked fine (I copied an existing forum and did not install a new one) and the performance is really good but there are some big problems left:
- preg_replace with the /e modifier (fixed in 3.1.0)
- File uploads: Due to the design of Google App Engine the filesystem is not writable. To store files you need to use Google Cloud Storage which can be accessed from PHP with a stream wrapper (e.g. gs://storage-bucket/123.txt)
- E-Mail - Google App Engine has its own Mail-API instead of PHP's mail() function. (using SMTP mail might work)
Is there any way to tell phpbb to upload files to gs://storage-bucket/ instead of files/ and images/avatars/upload?