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From "Jeremy Brooks" <>
Subject RE: clusters
Date Tue, 09 May 2006 16:19:17 GMT
As a caveat to the E-mails about caching pages using a proxy, the usefulness
of such depends on how much traffic your site will see to static pages.  In
our situation, the only static pages are our "contact us" page, "privacy
policy" ,etc.  Those pages don't get enough traffic to justify the
maintenance of setup overhead of a proxy. Our main page is not static and
neither are the product and category pages.  Actually over 99% of our pages
are dynamic with rotating specials and such.  The usefulness of caching on
pages via a proxy also depends on your typical landing pages.
If you have a customer click to your site to a page with dynamic content
(specials, session IDs in form data, etc) then caching to the most
frequently viewed pages is useless and even damaging/problematic.  

Regarding Round Robin DNS, this scenario will become a nightmare should you
loose a server that is not redundant on the same IP.  Even with a very short
TTL, your customers will see more downtime then they like and may go
elsewhere should you loose a server.  DNS load balancing is generally not a
wise load balancing method because it's NOT actually balancing load in real
The affect of round robin DNS is something akin to breaking up load sometime
last week and hoping it all works out today. It's not really an active
solution since servers die and nothing changes in the customers view for
quite sometime.  In fact, TTL must be reached before other DNS servers
update their cache and most importantly, your customers PC must actually
begin to us the new IP to connect!  So, now you're dependent on DNS client
caching on your customers PCs...   Not good.  On a Windows PC this can mean
restarting the browser, on an OSX machine this may mean restarting the damn
machine (really, I've experienced this).

Go with IPVS as a base and proxy if it makes sense.  Use DNS load balancing
only if you have redundancy on each node connected to each IP and if load
balancing public IPs is to much pain otherwise.  

You can use IPVS in several different topologies or you can mix them to get
what you want. 

-Jeremy Brooks

> -----Original Message-----
> From: Jeremy Brooks [] 
> Sent: Tuesday, May 09, 2006 10:26 AM
> To: 'Perrin Harkins'; 'Ken Perl'
> Cc:
> Subject: RE: clusters
> We use Ultra Monkey (IPVS) to cluster our E-com site with 
> commodity hardware.
> Your application needs to cache sessions in a common database 
> table in order to make session work consistantly.
> > -----Original Message-----
> > From: Perrin Harkins []
> > Sent: Tuesday, May 09, 2006 7:28 AM
> > To: Ken Perl
> > Cc:
> > Subject: Re: clusters
> > 
> > Ken Perl wrote:
> > > Is it possible to make a modperl application to run in cluster?
> > 
> > Of course.
> > 
> > > if yes, how to do that?
> > 
> > The same as any other web system -- multiple machines, a load 
> > balancer, shared data on a database or other system.
> > 
> > > any doc?
> > 
> > Tons of them.  Practically any doc about clustering will apply.  I 
> > wrote one ages ago about one mod_perl site I worked at:
> >
> > 
> > Is there some specific part you're having trouble getting your head 
> > around?
> > 
> > - Perrin

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