Viability of nginx instead of hardware load balancer?

[Barry Abrahamson]

On Sep 15, 2009, at 9:41 AM, John Moore wrote:

> I'm working on a project where it's critical to minimize the  
> possibility of a single point of failure, and where there will be  
> quite high traffic. Currently in another version of the system we're  
> using nginx as a remote proxy server for Tomcat, but the current  
> plan is to use a hardware load balancer in front of a Tomcat cluster  
> (or a cluster of nginx+Tomcat instances). I'm wondering, though,  
> given the extraordinary performance and reliability of nginx,  
> whether we might be able to omit the hardware load-balancer and use  
> instead a couple of dedicated minimal nginx servers with failover  
> between them. If anyone has gone down this path and has some good  
> ideas and/or useful experience, I'd be keen to hear from them.

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.  I am  
not sure how to reduce this, it seems like a necessary evil of running  
something like this in user space.  I have wanted to try FreeBSD 7 to  
see if it performs better in this area, but haven't had a chance yet  
(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.

Hope this helps,

Barry

--
Barry Abrahamson | Systems Wrangler | Automattic
Blog: http://barry.wordpress.com