These `error_page` statements are for responses that come back from **non**-proxied requests (or if the app is down). Since we're only serving static pages we can only get a 404 back.

When an app node sends out a 401/403/404/418/500/.. the UI will have to pick that up and do the appropriate thing (show a notification or redirect to /401, /403, /404, /500 ..)