While investigating a serious performance issue over the last 24 hours I discovered an issue whereby some of our CSS files were being combined but were not being rewritten by mod_pagespeed. After much hair pulling, far too many hours spent in front of
less and friends, I finally tracked down the solution. I added a
ModPagespeedLoadFromFile directive for every CDN domain and now all our resources are being properly rewritten.
I think, but I’m not sure, that mod_pagespeed tries to retrieve from the same domain as the request arrives on. So if you’re rewriting resources from
cdn.xmpl.tld, when the request arrives at mod_pagespeed with a Host header of
cdn.xmpl.tld, mod_pagespeed tries to look up every resource on the
cdn.xmpl.tld hostname, instead of doing a reverse lookup through the