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Søren Neigaard wrote:
Saturday, February 23, 2002, 11:57:18 AM, Joe wrote:
JC> That isn't clustering--it's high availability (as your subject tells us
JC> you already know). So why search for Linux cluster, when you really
JC> want Linux high availability? ;-)
JC> Check out www.linux-ha.org. Set up mon or similar tool so that it can
JC> notice a failure of your app and bring up the backup server, and you're
JC> golden. No need for LVS, or much of anything else for simple high
JC> availability.
Thanks :)
If you don't mind, I will ask one more newbie question. If I want a
cluster to improve performance on my Java application server. Is it
the required that my application server is specially written to
support this, or is it handled somewhere else? That is, can all
software benefit from a cluster. just as long as it uses threads?
There are two types of cluster...you're talking like you want a Beowulf
or Mosix style cluster, but you really probably don't. ;-)
An application server almost always just needs load balancing with
client session persistence, not computational clustering. You seem to
be thinking you need computational clustering, which is what Beowulf and
Mosix do. I kinda think you need load balancing, which is what an LVS
cluster does. But I don't know your app, so maybe I'm wrong.
If your app is serving a large number of independent clients entirely
independent application sessions (possibly with a shared database
backend), then you just need load balancing. This requires no changes
to your app, except as needed to make sure any backend systems can
maintain the level of synchronicity your application requires.
And, if you do need computational clustering, you'll probably need to
rewrite at least major parts of your app. And you'll want to spend the
next 6 months to 3 years studying the intricacies and complexities of
the topic to fix all of the issues you run into while rewriting. ;-)
The notion that just anyone can set up a Beowulf and instantly begin
performing super-computer style calculations and data manipulations is
quite exciting, but patently fictitious. It isn't a 'weekend
project'...it's more of a two year project, for computer science majors.
;-)
So to answer you last question...can all software benefit from a
cluster? Of course not. But if you're talking client/server apps, then
the answer gets much closer to yes. LVS will balance almost any
client/server software you can name, probably including your application.
--
Joe Cooper <joe@xxxxxxxxxxxxx>
http://www.swelltech.com
Web Caching Appliances and Support
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