Hello,
Does anyone have some wisdom they can impart to me concerning writting VU scripts used to test a load balancing architecture? Unfortunately, when recording a VU script from the client->load balancer->web server the load balancer is transparent to the recording mechanism and when I play the script back it always plays back against the same web server (unless I manually change the servername ort address in the code).
Are you sure? What about if you step up the volume of VU's?
I am a little bit concerned because at my site they are proposing to bring the Big IP LB in as well. I was assuming the BIG IP machine just has its own IP address and you start to record against that address. It probably gives you back the address of the server that it has assigned you to early on in the seesion. If you can parse out this address and use in the rest of your script you could succeed in running the script against all your servers by the discretion of the Big IP machine. I also found out that the Big IP machine also sends cookies to the clients and queries for these cookies when they connect again. The machine does that to lead you back to the server that you were originally connected. Check with your network and infrastructure folks if they have enabled anything like that.
Let me know what you find out.
Some load testing tools have a feature called "spoof IP". This feature changes the IP of each VU as it is sent to the server. This feature is included specifically to address the problem you are experiencing.
With the Rational Tools the term is "IP Aliasing".
But I know that BigIP can be setup to be a bit more sophisticated than just being a IP-based Load Balancer. Maybe there is a solution?
What you need to find out is HOW the load balancer is dividing up the load. Common methods are "Round Robin" which sends each new user to the next Web Server in the rotation, "Sticky IP" which sends every request from a new IP address to the next Web Server in the rotation, or true "Load Balancing" where the load on each server is monitored and requests are intelligently redirected.
With Sticky IP, you may need to do the IP Aliasing discussed above.
If you have true Load Balancing, as Roland suggested, you may just not be generating enough load for the balancer to start using a second server.
You're best bet would be to find the person(s) who configured the balancer, and have them explain to you the methods/configurations, and then have them monitor it as you execute a load test. Together, you should be able to easilly see the problem and likely the solution.
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