I'm getting behavior I don't quite understand from my Apache reverse proxy.
I have a back end server which returns a 503 using app_offline.htm
during certain processes.
When this occurs I receive a traditional Apache 403 error:
You don't have permission to access / on this server.
Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.
If my back end server is unavailable and mod_proxy can't connect I do see my custom error screen, but a generic 503.. I'm guessing that I need to pass that 503 back from mod_proxy to Apache for handling, but I'm not sure how.