If you have seen my presentation about Varnish on the PHPBenelux Conference 2011, you know already that Varnish is a really great reverse proxy caching system that can boost your website performance massively. A somewhat lesser-known feature of Varnish is that its VCL-configuration is very powerful. So powerful in fact, that we could easily add, replace or modify headers to and from Varnish. I have shown for instance in my presentation that you can send a X-Cache-Hit or X-Cache-Miss header to display if a request has been fetched from the either the Varnish cache or has been retrieved from the back-end.

After my presentation, Andreas Creten approached me, asking about mobile device detection in Varnish. He had problems on a website keeping up with all types of mobile devices to detect in the correct way. That question didn’t result in a direct answer, but did trigger something…

What if Varnish could figure out if the visitor was working on a mobile browser, and if so, set a flag to the back-end servers so it could display a mobile site? Impossible? No. Actually, it’s quite easy… read more…

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