Chapter 9. Test Environment Construction and Tuning

A good stress test uncovers any problem areas before deploying the web site to production. The time and expense of performance tests pays off in the gains realized in customer satisfaction and overall site reliability. So far, we've discussed building good performance tests for your web site. Now let's cover building a realistic environment in which to run these tests.

In short, you cannot go cheap in building your test environment. Poor infrastructure impacts performance and stress tests more than any other type of tests you'll run against your web site. Don't expect to meet your web site performance goals if you build the test environment with cheap cable, underpowered client machines, and low-bandwidth networks. To get the most out of your performance test efforts, the test environment must mimic the production environment as closely as possible, given the ever-present constraints of time and expense. Obviously, if the web site contains hundreds of servers, you cannot recreate a huge server farm for a performance and stress test. In these cases, scale down the test to a few machines, keeping the scale proportional to the production system. Figure 9.1 shows a typical small test cluster with peripheral systems.

Figure 9.1. An example test environment

Proportion remains important in "scale environments" in other ways as well. Again, if the 20 machines in the production cluster use 200 database connections, assume that the small cluster of two machines needs 20. The same goes for network bandwidth, test clients , and other resources you might need for the test. Also, when using a smaller environment, keep in mind the behavior of the system at two servers might be drastically different than with twenty. The web site team must test scalability in a small-scale environment.

Of course, the reduced costs of small-scale environments lead to reduced coverage of all the situations your large-scale web site faces in production. If you test with a small-scale environment, you may encounter undiscovered problems when you move to production. In fact, you may encounter problems you can only recreate on the production web site. The best test environment remains a full-scale reproduction of the production web site, whenever possible.