Comments on: DNS-based load balancing for virtual users

By: Stuart Moncrieff

Stuart Moncrieff — Fri, 06 May 2011 05:15:00 +0000

Today I used this when I had a web application that was giving an error message for the first page that was loaded. This was happening approximately 50% of the time.

I bypassed the load balancer to hit each of the web servers directly, and found that half of the web servers had been misconfigured.

Using this technique helped speed up the responses of the infrastructure support team, who now had a list of broken servers to look at, instead of having to check all the servers.

By: Nick Johnson

Nick Johnson — Thu, 17 Dec 2009 06:17:45 +0000

very useful info… here’s some additional considerations….

- if this is being done for the purposes of bypassing a Load Balancer (LB), run at least once in vugen (with full logging “advanced trace” enabled) to ensure the IP address of the LB is not used by the script.

- absolute references within pages to components will not be replaced with the IP address specified in the modified code and thus should be checked for on playback & re-recorded explictly in URL mode if they exist.

- also, other hosts that may be referenced in the script may not be replaced with the desired IP address, and thus could send you back to the LB (or other servers) – these are worth checking for too.

cheers
Nick

By: Stuart Moncrieff

Stuart Moncrieff — Wed, 07 Oct 2009 22:29:33 +0000

Speedmaster – no, that is not what “sticky” load balancing is.

Cheers,
Stuart.

By: Speedmaster

Speedmaster — Wed, 07 Oct 2009 19:40:10 +0000

>> “The visitor will usually cache the results of the DNS lookup for a period of time (30 minutes in Internet Explorer), so their requests will all be sent to the same web server”

I think this is what is sometimes referred to as “sticky” load-balancing?

By: Stuart Moncrieff

Stuart Moncrieff — Wed, 04 Mar 2009 04:34:17 +0000

Tomer had an interesting alternative solution to this problem, which avoids the severe limitation that this solution has for pages that have off-site resources.

His solution was to modify the hosts file entry for the domain name on each iteration and to turn off DNS caching under Runtime Settings > Internet Protocol > Preferences > Advanced Options, so that VuGen would pick up the new value.