[imp] single machine versus load balancing

[Oliver Kuhl]

Zitat von Eric Rostetter <eric.rostetter at physics.utexas.edu>:

> Quoting Charlie Reitsma <reitsmac at denison.edu>:
> 
> > setoolkit reports the CPU is overloaded (I'll see load average over 50
> > sometimes). Users will experience a minute between clicks sometimes. The
> > IMAP box rarely exceeds 50%. The high load is http clients.
> 
> Besides the usual tuning, consider a php accelerator.  It may help enough.
> But probably you do need a faster box if you want real fast access times
> during peak hours.
The accelerator is very important. I have good experiences with the ionCube:
http://www.php-accelerator.co.uk/

> > Reading the scaling article on the horde site I get the feeling that
> > there are sites handling my population size on a single box without
> > problems.
> 
> Yes, I've done it, but on a dual cpu machine.  You will be slow with
> a single 500Mhz cpu, IMHO.
This one is too slow. You should better take a dual cpu machine.

> > Should I consider load balancing with round-robin DNS or a
> 
> Simple RR DNS will probably result in session problems, unless you
> somehow share the sessions (should be possible since you say you use
> sql for sessions).
A dual cpu machine would be easier to manage, but a load-balancing gives you
redundancy.

I set up an RR DNS with two boxes. You can bypass the session problem by
redirecting the user directly to one of the machines. I set up my apache with
two virtual hosts on both machines. One takes the RR-name (i.e.
webmail.example.com) and the other one the machines name (i.e.
webmail1.example.com).
If a user openes webmail.example.com and is taken to the ip of machine no.1, the
apache redirects him directly to webmail1.example.com (which is on the same
machine). Every following action will go to webmail1 then. And this is the
disadvantage of the solution: It's not really a load-balancing, because nothing
takes a look at the load of the machines.

> > If I were to do load balancing I
> > would continue to use Sun Netra X1 and look at load balancing hardware
> > as well.
> 
> If you want to load balance, hardware is the way to go IMHO.  RR DNS just
> isn't going to help during peak times, and won't help if one machine goes
> off the air the way a good hardware load balancer will.
Thats right. And Netra X1 will be ok. If you look at the price, 2 Netra X1 and a
hardware loadbalancer could be the same price as a sun dual cpu machine.

Gruss,
   Ollie.