Re: clusters of computers - that are all the same?

[Alan Robertson <alanr@unix.sh>]

Charly Jones wrote:
> 
> Is the framework intended to include clusters of homogenous computers and
> operating systems?  Or is it intended to include different hardware
> and operating systems?  Different releases of Linux?  Linux machines
> clustered with Unix machines?
> 
> I am a newcomer to this topic...

Good question!  I've never answered it directly before (this is a new
proposal).

The framework itself is agnostic.

It does not / should not enforce homogeneity of any kind, nor rely on it.

Framework *components* may or not be suitable for a heterogeneous
environment - depending on the component.  It's up to the component. 
Myself, I like components that allow heterogeneous nodes in the cluster, but
the implementator of a component has the freedom to allow or disallow any
particular mix of nodes.

For example, high-bandwidth HPC interconnects may only work between
homogeneous systems.  There are good performance reasons why this may be
required - and the framework doesn't dictate how the components work under
the covers.

However, HA components should work across a mix of different releases of
OSes, and different releases of application software, and framework
components.

This is because HA systems have to work in an environment of rolling
upgrades, where different software releases introduced into the cluster one
node at a time.  This is guaranteed to introduce all kinds of interesting
differences into the cluster - and these differences have to be handled
well.

The fundamental control messaging system is XML-based which is very amenable
to dealing with these kinds of differences, and providing tools and
infrastructure which makes it easier and more natural for the components to
do the same.

	-- Alan Robertson
	   alanr@unix.sh

Linux-cluster: generic cluster infrastructure for Linux
Archive:       http://mail.nl.linux.org/linux-cluster/