App error pages are replaced by custom error backend
Our new custom error backend for the ingress controller works a little too well: if an app generates a 404 or 500 error, any nice error page it serves -- think custom styled wordpress 404 for example -- gets replaced by the generic Stackspin error. That's not what we want.
We can fix this for now by not having any 404 or 500 errors from the custom error backend, just 503. We should later investigate if we can let ingress-nginx make the distinction between a 404 from an app and a 404 from the ingress controller itself, for which we do want to use the Stackspin error page.