Kristian Lyngstol's Blog

A free software-hacker's blog

Varnish Training

As anyone who’s worked with me should realize by now, I’m big on documentation, be it source code comments or other types of documentation. The only reason I’m not more active in the documentation section of Varnish Cache is because I’ve maintained our (Varnish Software’s) training material ever since Tollef Fog Heen wrote the initial slides in 2009.

I’ve held the course more times than I can remember, and usually done improvements after every course. Others have also held the course, including Redpill Linpro’s Kacper Wysocki, maintainer of security.vcl and Magnus Hagander (Postgresql god/swede). Feedback and gradual improvements have turned a set of slides into a pretty good course material.

We recently started holding on-line courses too. This revealed several new challenges. The obvious challenges are things like getting basic voice communication working (it sounds easy, but you’d be amazed…). It was also interesting when I held the course in my apartment on Australian time, and my ISP decided to perform maintenance on my cable modem (it was 2AM local, after all). So I’ve had to hold the course on a 3G connection, communicating with Australia. Fun. Then there’s the lack of or severely reduced feedback, which presents challenges in how we do exercises and generally deal with the course. In a class room I can easily determine if the participants are able to keep up, if I’m going too slow or too fast and whether or not a subject is more interesting than an other. All of that is, at best, very difficult in an on-line session.

The last few weeks I’ve finally gotten around to merging the sysadmin course with the web development course that Jérôme Renard has written for us. It proved the perfect opportunity to give the course an other big update. While the course was already updated for Varnish 3, I’ve made several other Varnish 3-related additions. More importantly is that the flow of the course has changed from one oriented on Varnish functionality to tasks you wish to accomplish with Varnish. Instead of teaching you about Varnish architecture first, then Varnish parameters, the course now has a chapter devoted to Tuning.

Instead of just throwing in purging or banning when talking about VCL, there’s now a chapter called Cache Invalidation, that attempts to give broader understanding of the alternatives you have and when to use which solution. Similarly, there’s a chapter called Saving The Request, which starts out with the core Grace mechanisms, moves on to health checks, saint mode, req.hash_always_miss, directors and more.

There are several reasons I write about this. First of all: I’m very excited about the material. I’ve worked on it regularly for several years, doing everything from hacking rst2s5, tweaking the type setting and design to updating the content, reorganizing the course and of course holding it. It may seem like one big marketing stunt, but I can promise you that I never blog about something I’m not passionate about, regardless of whether it is work-related or not.

The other reason is that I’m holding the course next week. This will be the first time we hold it using the changed structure. I would have wanted to hold it in a class room first, but holding it on-line is still exciting.

If you wish to participate, head over to and convince your boss it will be awesome!

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