Nginx/varnish can also catch Content-type: text/plain (or text/php?) and treat that like a 5xx response. Yes, that's a bit of a hack, but unless tumblr needs to

Nginx/varnish can also catch Content-type: text/plain (or text/php?) and treat that like a 5xx response. Yes, that's a bit of a hack, but unless tumblr needs to serve text-files (which I doubt) it's a legit safeguard.