On Sat, Nov 01, 2003 at 10:07:25AM -0600, Nick Reinking wrote:
I took the
number "90%" as an example. You can make it 99% if you like,
the result remains the same: One loadbalancer in front of two webservers
reduces availability. Simple maths.
I also think that load balancing a farm of web servers is the way to go,
I just want to point out that availability will not increase.
This is not only wrong, but silly at the same time. Load balancers have
better availability than web servers - if they didn't, nobody would even
bother with them. They'd just have crazy schemes where web servers
automatically take over for each other when others go down.
Plus, consider that when you add a load balancer in front of a farm of
web servers, you no longer care about the availability of the web
servers - because when a web server goes down, the load balancer takes
care of it. So, by your 90% rule of availability, given one load
balancer and four web servers:
10% (load balancer downtime) + (.1 * .1 * .1 * .1 = .0001) = 10.0001%
downtime. Not noticable over just the plain 10% of having just a web
server. When you take into account the extra speed you get with the
load balancer, plus the fact that load balancers are more reliable than
web servers, it's a no brainer.
You got my point! Extra speed: yes. Extra reliability: Not really.
Not if you add a single, non clustered load balancer.
And to strengthen it: Extra speed is what we need, here I agree completely
with Lars.
Regards,
JeLuF