“We are using Varnish heavily for caching images. All of the images on WordPress.com and Gravatar are cached via Varnish. We have about 60 varnish servers deployed on WordPress.com and 10 on Gravatar. Each Gravatar varnish server is serving 3ish thousand requests per second. My gripe with Varnish is that whenever we upgrade, we seem to run into new performance/optimization problems which require lots of time to resolve. As a result, WordPress.com is still running an older version of Varnish. Persistent caching (across server restarts) should be introduced in Varnish 2.1 which should be cool.”
http://serverqa.wordpress.com/
“We are using nginx as a reverse proxy (load balancer) serving tens of
thousands of requests per second across various large sites
(WordPress.com, Gravatar.com, etc). We deploy our nginx reverse
proxies in active-active pairs using Wackamole and Spread to control
the floating IPs for high availability. Our busiest load balancers
(req/sec) are serving about 7000 req/sec and the most traffic per
machine is in the 600Mbit/sec range. We could push each machine more,
they aren’t maxed out, but we like to leave some room for growth, DoS
attacks, hardware/network failures, etc. The bottleneck for us seem
to be the large number of software interrupts on the network
interfaces cause the boxes to become CPU bound at some point.
(we are running Debian Lenny mostly).
We are using “cheap” commodity hardware.
2 x Quad-core AMD or Intel CPUs
2-4GB of RAM
Single SATA drive
2 x 1000Mbit NICs
Since it is so easy to deploy more servers, it’s super easy to scale,
and this configuration has been ultra-reliable for us. Most of the
failures we have had are from human error.”
