rails 404 422 500 completely blank
I don't think Heroku uses the .html files like Passenger or Mongrel do. You may need to catch and handle your own exceptions through two basic mechanisms:
- Create an exception handler with rescue_from in your ApplicationController for anything that might explode, both specifically and up to and including Object.
- Create a default route to catch anything that isn't otherwise routed.
If you bust out of your routing table, or trigger a "500" error, it's because of exceptions. These need to be handled or you'll get a blank screen unless the web server is configured otherwise.
Apache can be configured to do this with the ErrorDocument directive.