Le Wiki Koumbit
Implementation of the CachingService with Varnish.
Contents
Installation & Configuration de Varnish
This documentation is mostly outdated. Varnish is now managed through Puppet and the configuration there is the reference.
Installation de Varnish
The version of Varnish which is currently packaged in Debian Stable is 1.0.2. This package currently has a few known errors. For a production site it is therefore currently recommended to build Varnish manually from source instead. For a full list of the known issues for the Debian package, refer to the Debian bugtracker (http://bugs.debian.org/cgi-bin/pkgreport.cgi?pkg=varnish;dist=stable).
On créera donc notre propre package à partir des sources. J'ai pris le backport uploadé sur backports.org pour recompiler une version amd64, sur builder.koumbit.net.
Voici la configuration déployée par Puppet dans /etc/default/varnish:
DAEMON_OPTS="-a :80 \
-f /etc/varnish/puppet.vcl \
-s file,/var/lib/varnish/$INSTANCE/varnish_storage.bin,1G"Le fichier /etc/varnish/puppet.vcl va varier selon les frontends, mais pour l'instant il est commun à tous les cache potentiels:
backend default {
set backend.host = "127.0.0.1";
set backend.port = "8080";
}
backend example {
set backend.host = "example.koumbit.net";
set backend.port = "80";
}
sub vcl_recv {
if (req.http.host ~ "^(.*\.)?example.net$") {
set req.backend = example;
}
}See VarnishMaintenance for more complete configuration examples.
Basic DNS configuration
/etc/bind/db.209.44.112
78 IN PTR cache.koumbit.net. ; cache web (varnish)
/var/alternc/bind/zones/koumbit.net
cache IN A 209.44.112.78
Other configuration examples
More configuration snippets are in the VarnishMaintenance page as they are regularly modified and tweaked depending on the requirements of the site.
Systemd
Starting from jessie, debian uses systemd. This means that /etc/default/varnish is not read anymore, and any daemon options passed to the init script through there previously are now not effective anymore. This can mean that varnish will not bind to any IP, and use the default of 256Mb of cache instead of your setting.
In order to fix this, we copied /lib/systemd/system/varnish.service to /etc/systemd/system/varnish.service and then edited it in order to override the ExecStart line and add the arguments that were set in $DAEMON_OPTS in /etc/default/varnish (don't forget to extrapolate $INSTANCE because systemd won't do it for you).
This was somewhat documented in the debian wiki but that documentation was wrong. Also, since our solution feels like the wrong approach, we didn't modify that wiki page.
Performance tuning
Varnish is very robust. But the bigger you scale the traffic it handles, the more it needs some fine-tuning.
This page informs about some recommendations from the varnish project itself: https://www.varnish-cache.org/trac/wiki/Performance
Most notably:
use malloc storage type instead of file
- bump thread pool up a bit
push thread_pool_add_delay down
- use grace mode to make varnish serve stale objects while is re-fetching them from the backend
- put the shmlog into tmpfs
References
- Varnish and Drupal
- issues with cookies:
- packaging:
first backport (now something similar uploaded to backports.org, thanks micah!)
- varnish docs: