====== varnish ======

Varnish is a web accelerator.

Wikipedia: A web accelerator is a proxy server that reduces web site access times. They can be a self-contained hardware appliance or installable software.

==== Configuration ====

Edit ''/etc/varnish/default.vcl'':
<code>
backend default {
  .host = "127.0.0.1";
  .port = "80";
}
</code>

The web server must accept connections on that IP address and serve the content.  A standard virtualhost would listen only on public IP addresses.

Start varnishd:
<code>
varnishd -f /etc/varnish/default.vcl -s malloc,1G -T 127.0.0.1:2000 -a 0.0.0.0:8080
</code>

==== Notes ====

  * Varnish can have several backends defined and can you can even join several backends together into clusters of backends for load balancing purposes.
  * Be aware that every object that is stored also carries overhead that is kept outside the actually storage area. So, even if you specify -s malloc,16G varnish might actually use double that. Varnish has a overhead of about 1k per object. So, if you have lots of small objects in your cache the overhead might be significant.
  * You can use Varnish to cache content from different servers, effectively splitting URLs across many backends.  Fex: http://domain/ pulls from 1.2.3.4:80 while http://domain/images/ pulls from 5.6.7.8:80.
  * Varnish has a "saint mode" where it will only send a cache if there is a bad request returnedV from the original webserver.  Fex: Site returns HTTP 500 because it is overloaded, so Varnish serves stale content.  See: [[https://www.varnish-cache.org/docs/3.0/tutorial/handling_misbehaving_servers.html#saint-mode|here]]
  * Varnish can act as a high availability server, balancing load between two backends.  Fex: Two  servers on different IP addresses are handling the backend load.  See: [[https://www.varnish-cache.org/docs/3.0/tutorial/advanced_backend_servers.html|here]]

==== Ubuntu ====

<code>
curl http://repo.varnish-cache.org/debian/GPG-key.txt | apt-key add -
echo "deb http://repo.varnish-cache.org/ubuntu/ lucid varnish-3.0" >> /etc/apt/sources.list
apt-get update
apt-get install varnish
</code>