Load balancing vusers without a load balancer

Recently I ran a test at a company which had a performance test environment with multiple web servers, but no load balancer. To spread my virtual users evenly across the web servers, I made a simple modification to my script.

First, I created a file-based parameter containing my web server names.

Next, I parameterised the server name part of the URLs in my web_url() and web_submit_data() function calls.

web_url("Login", 
    "URL=http://{ServerName}/login.do", 
    "TargetFrame=", 
    "Resource=0", 
    "RecContentType=text/html", 
    "Referer=", 
    "Snapshot=t1.inf", 
    "Mode=HTML", 
    LAST);

So, when the script ran, the virtual user would would choose a web server at random on every iteration.

...and that was it. I didn't say it was going to be hard. :)

Of course, my Test Summary Report was very clear that one of the limitations of the Performance Test cycle had been that there was no load balancer in the test environment, so the stability and performance characteristics of this component in the Production environment could not be predicted.