On Fri, Oct 31, 2003 at 09:18:43AM -0800, Jimmy Wales wrote:
I have had very good success in the past using iptables and a
configuration that looks a lot like this picture:
http://www.ultramonkey.org/2.0.1/topologies/lb-eg.html
Of course, I did this years ago, and the "poor man's" way -- I think
there are probably packages (like ultramonkey!) that are quick
solutions now.
The beauty of this kind of architecture is:
1. high availability -- if one webserving node falls over, traffic
automatically goes to the ones that are still up
Well, the architecture shown does not increase availability since
it adds a single point of failure. Let's assume a server's availability
is 90% (It's higher, of course, but numbers will become too ugly for this
example). Having one webserver and one database server the overall
system availability would be 81%.
Clustering two web servers will increase the web servers availability
to 99%. But now the system has three components: Load balancer (90%),
Web servers (99%), database (90%). That's a total availability of 80.19%.
Oops.
If we really would need to increase hardware availability, we would have
to either have a cluster of load balancers or a cluster of webservers
using round robin DNS and IP takeover.
2. easy expandability -- just add more webservers, at
$2000 a crack
for 'good enough' machines, and install the software and there you go.
That's true, if TeX and image directory can be shared or something.
Regards,
JeLuF