Long time no see !

It has been quite a while, and I have been up to lots of interesting things, mostly under NDA! Journalism has been sadly low on my priorities. Once a couple of public launches are out of the way I will have more to say on that.

In the mean time, here are some thoughts on varnish, one of the unsung heroes of everything from twitter to the larger public blogs. It is a so called “reverse proxy” – a really smart cache that is fantastic for allowing me to concentrate on two things separately – making great sites based on rapid dynamic technology, and scaling.

Varnish is no magic bullet – it works best for sites that are personalised and dynamic but where the actual number of things people are looking at on mass at any one time is relatively small.

I am currently using it to front a search site, not so much for the caching but because it is an interesting way of doing two things – basic load balancing and fail-out, and page assembly. In my case I use ESI in varnish to composite fragments dynamically assembled by a set of google appliances with elements that change less often.

It has worked out fairly well, with a couple of gotchas – gzip compression and ESI are not happy bed-fellows with varnish, and so I have to force requests to the appliance not to use compression by filtering the header as it comes from the browser. Varnish also does not handle SSL, so you need to terminate any SSL “around” varnish with port mapping trickery to something that can handle it like apache.

Given that ESI works with everything from F5 load balancers to akamai to open-source proxies, I think it a technology that everybody need to get a handle on, a better way to assemble pages that scales massively.


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