[Beowulf] Transparant clustering

[Lombard, David N]

On Fri, Nov 14, 2008 at 01:41:16AM -0700, Serge Fonville wrote:
> Thanks for the response (and for the questions :-))
> 
> I'll try and elaborate a bit more.
> I currently have two equal systems. (XEON 3220,8GB,80GB RAID1)
> I want to run a couple of websites (using Tomcat) and two database servers (PostgreSQL and MySQL)

That's a very different type of clustering.  This list, the Beowulf list,
is about about clustering for HPC, to increase compute performance, usually
for scientific and engineering calculations.  See below.

> I have contintued reading a lot and I think I am starting to have a clear idea on what is possible
> Basically I want it to appear as a single system to the outside world while in fact there are more (currently just two).
> They should divide all usage of resources equally. If one goes down the other notices and takes over everything, if it comes up again they are synchronized (I am aware of the split brain issue) either server has four network interfaces and can also be connected through an RS-232 cable.

There are hardware and software solutions to this problem.  At the conceptual
level, you have a system--the load balancer--that routes incoming requests to
one-of-N backing servers.  If any of the backing servers fails, it's simply
ignored and future incoming requests are routed to the remaining server(s).
As long as the remaining server(s) can handle the load, all is well and your
service is provided.

Here's LVS, a software solution: <http://www.linuxvirtualserver.org/>
You may also want to consider Linux-HA to ensure your LVS server is robust:
<http://www.linux-ha.org/>

There are many other details to consider, but you'll learn of those as you
research more appropriate solutions.

HTH
-- 
David N. Lombard, Intel, Irvine, CA
I do not speak for Intel Corporation; all comments are strictly my own.