A while back I wrote a plugin to take care of a particular client traffic problem. As the traffic came in very quickly and unexpectedly, I had only minutes to come up with a solution. As I knew Varnish pretty well, my initial reaction was to put the site behind Varnish. But, there’s a problem with Varnish and WordPress.<\/p>\n
WordPress is a cookie monster. It uses and depends on cookies for almost everything – and Varnish doesn’t cache assets that contain cookies. VCL was modified and tweaked, but, the site was still having problems.<\/p>\n
So, a plugin was born. Since I was familiar with ESI, I opted to write a quick plugin to cache the sidebar and the content would be handled by Varnish. On each request, Varnish would assemble the Edge Side Include and serve the page – saving the server from a meltdown.<\/p>\n
The plugin was never really production ready, though, I have used it for a year or so when particular client needs came up. When Varnish released 3.0, ESI could work with GZipped\/Deflated content which significantly increased the utility of the plugin.<\/p>\n
If you would like to read a detailed explanation of how the plugin works and why, here’s the original presentation<\/a> I gave in Florida.<\/p>\n