Re: A proposal for a General Clustering Framework

["Bill Todd" <billtodd@foo.mv.com>]

----- Original Message -----
From: "Alan Robertson" <alanr@unix.sh>
To: "Bill Todd" <billtodd@foo.mv.com>
Cc: "linux-cluster" <linux-cluster@nl.linux.org>
Sent: Tuesday, June 05, 2001 6:18 PM
Subject: Re: A proposal for a General Clustering Framework


> Bill Todd wrote:

...

 I'll also point out that it
> > is often easier (and/or safer) to define upgrades (at least those that
> > affect protocol syntax or semantics) such that all nodes get upgraded
(one
> > by one, with no general outage) to new software that continues to use
the
> > old protocols - and then after all upgrades are complete, a synchronous
> > cluster-wide transition to the new protocols occurs.  Among other
things,
> > this avoids proliferation of run-time conditionals that depend on the
> > capabilities of each member.
>
> This is exactly what this technique is designed to support - allowing the
> new code to use the old data formats.
>
> > In general, if one can avoid the requirement to support

*protocol*

 version
> > heterogeneity across a cluster, life can be a lot simpler.  While

*protocol*

 version
> > heterogeneity is clearly required in general networks (where systems are
> > under the control of completely independent organizations), it's not
clear
> > that (at least what I think of as) a cluster can't reasonably impose
such a
> > constraint.
>
> It's very clear that, in general, one cannot avoid this requirement.

Please reassess your statement in the light of my clarification above:  if
you still believe it, either you don't understand what I was saying (since
what I was saying has no adverse impact on availability) or you appear to
believe that a 'cluster' must support the same degree of node
protocol-version diversity that a WAN must (which I consider a marginal
'might be nice but is likely hell-on-wheels to support' rather than a 'clear
requirement').

- bill

  It's
> like saying "if one could avoid machines ever going down, one wouldn't
need
> an HA system".  OK.   What you said is true -- it's just not very helpful.
> Because, it's clear that the infrastructure must support this obvious and
> common need.
>
>
> -- Alan Robertson
>    alanr@unix.sh



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