Varnish

If you have multiple virtual hosts being handled by the same server you some times want some sort of QoS to apply to your caching. You might want to reserve a certain amount of memory for each virtual hosts. Let me show you how it can be done.

Once every querter there is a VDD - Varnish Developer Day. We typically gather between 8-16 people that are interested in Varnish development and discuss where we are and where we wanna go.  The last VDD was held in Stockholm, in the offices of Redpill Linpro in Solna. Roughly the outcome was something like this.

Varnish logs a lot. Sometimes it is a bit too much and verifying that your VCL works the way it is supposed to can be a bit of a bother, especially on a busy server. The new logging in Varnish 4  help a lot, but a lot of the time its easier to just a add a header or two to indicate what is happening.

Grace mode has since its inception in Varnish 2.1 been a key feature in Varnish. Initially a feature to mitigate thread pile-ups and the resulting thundering herd was soon adopted to other uses, mainly having Varnish to continue to serve requests ... [More] when the backend got in trouble. As part of the rework done with the threading model in Varnish 4.0 things changed and grace got somewhat changed semantics. The main change being Varnish is now capable of delivering a stale object and issue an asynchronous refresh request, thereby removing the penalty the first user gets when hitting a stale object. [Less]

Varnish Cache is a high performance web application accelerator that performs very good out of the box. The default parameters have evolved since the start of the project, and they fit fine for a small site or a developer installation. However in ... [More] order to run Varnish at scale you might want to tune it a bit to make it perform and scale even better. [Less]

tl;dr; when using Varnish 4 and bans via varnishadm, instead of “ban.url EXPRESSION”, use “ban req.url ~ EXPRESSION”. In Varnish 3.0 we had the ban.url command in the varnishadm CLI. This was a shortcut function expanding to the a bit cryptic (but ... [More] powerful) ban command. In essence ban.url just took your expression, prefixed it with “req.url ~ ” and fed it to ban. No magic. We deprecated this in Varnish 4.0, and now everyone has to update their CMS’s plugin for cache  invalidation. Hence this blog post. Perhaps it will help. Perhaps not. :-) Some references: https://www.varnish-cache.org/docs/trunk/users-guide/purging.html#bans – the proper docs on ban. Note the part about lurker friendliness. https://www.varnish cache.org/lists/pipermail/varnish-dev/2012-November/007399.html  - the discussion on the mailing list on removing it. [Less]

tl;dr; when using Varnish 4 and bans via varnishadm, instead of “ban.url EXPRESSION”, use “ban req.url ~ EXPRESSION”. In Varnish 3.0 we had the ban.url command in the varnishadm CLI. This was a shortcut function expanding to the a bit cryptic (but ... [More] powerful) ban command. In essence ban.url just took your expression, prefixed it with “req.url ~ ” and fed it to ban. No magic. We deprecated this in Varnish 4.0, and now everyone has to update their CMS’s plugin for cache  invalidation. Hence this blog post. Perhaps it will help. Perhaps not. :-) Some references: https://www.varnish-cache.org/docs/trunk/users-guide/purging.html#bans – the proper docs on ban. Note the part about lurker friendliness. https://www.varnish-cache.org/lists/pipermail/varnish-dev/2012-November/007399.html  – the discussion on the mailing list on removing it. [Less]

When answering questions in the forums, the mailing lists or our support, one of the most common topics to come up is virtual host. Virtual hosts are tricky and with Varnish and Apache/Nginx it is common to misconfigure it. Here I’ll explain how they actually work, how to verify it is working and how to set it up.

One of the two biggest changes in Varnish 4.0 is how the threads work. Varnish uses threads for doing all the heavy lifting and it seems to be working out quite well. In Varnish 3.0 one thread would service each client, doing whatever that client ... [More] wanted it to do. Within reason, obviously. These are very decent threads. The thread would deliver from cache, fetch content from the backend, pipe, etc. [Less]

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