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| + | ====== 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> | ||
