Contegix, an amazing internet hosting provider, recently ran some tests to determine the performance differences between various configurations of Apache and Tomcat. In the process of doing their testing, they used Pylot, an open source Python-based load testing tool, and BrowserMob. You can read their entire findings here.

What’s interesting is the use of both internal (Pylot) and external load testing (BrowserMob). This is something we strongly encourage our customers to do. In talking with Mark Rogers at Contegix, it was clear he saw a big difference between the type of traffic generated by Pylot and BrowserMob.

This shouldn’t be too surprising, since internal traffic runs on a super-fast local network, so the timings for opening and closing sockets are measured in nanoseconds rather than milliseconds. Content transfers so much faster and “cleaner” over a local network that the two styles of tests can look very different.

Internal load testing tools are great and simple, cost-effective ways to quickly validate that individual code/algorithms are executing in a high performance manner, but they don’t do a good job at telling you how your site will be experienced by real users from the real internet. That’s why external load testing is so important if you plan for anyone outside of your firewall to visit your site and have a good experience.

So next time you need to run some performance testing, don’t think of it as an internal vs. external question. Instead, use both for different purposes, like Mark and Contegix did, and you’ll always end up better informed than if you had only used one technique.

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