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Load / Stress Testing of Websites

1. The Importance of Scalability & Load Testing

Some very high profile websites have suffered from serious outages and/or performance issues due to the number of people hitting their website. E-commerce sites that spent heavily on advertising but not nearly enough on ensuring the quality or reliability of their service have ended up with poor web-site performance, system downtime and/or serious errors, with the predictable result that customers are being lost.

In the case of toysrus.com, its web site couldn't handle the approximately 1000 percent increase in traffic that their advertising campaign generated. Similarly, Encyclopaedia Britannica was unable to keep up with the amount of users during the immediate weeks following their promotion of free access to its online database. The truth is, these problems could probably have been prevented, had adequate load testing taken place.

When creating an eCommerce portal, companies will want to know whether their infrastructure can handle the predicted levels of traffic, to measure performance and verify stability.

These types of services include Scalability / Load / Stress testing, as well as Live Performance Monitoring.

Load testing tools can be used to test the system behaviour and performance under stressful conditions by emulating thousands of virtual users. These virtual users stress the application even harder than real users would, while monitoring the behaviour and response times of the different components. This enables companies to minimise test cycles and optimise performance, hence accelerating deployment, while providing a level of confidence in the system.

Once launched, the site can be regularly checked using Live Performance Monitoring tools to monitor site performance in real time, in order to detect and report any performance problems - before users can experience them.

2. Preparing for a Load Test

The first step in designing a Web site load test is to measure as accurately as possible the current load levels.

Measuring Current Load Levels

The best way to capture the nature of Web site load is to identify and track, [e.g. using a log analyser] a set of key user session variables that are applicable and relevant to your Web site traffic.

Some of the variables that could be tracked include:

the length of the session (measured in pages)

the duration of the session (measured in minutes and seconds)

the type of pages that were visited during the session (e.g., home page, product information page, credit card information page etc.)

the typical/most popular 'flow' or path through the website

the % of 'browse' vs. 'purchase' sessions

the % type of users (new user vs. returning registered user)

Measure how many people visit the site per week/month or day. Then break down these current traffic patterns into one-hour time slices, and identify the peak-hours (i.e. if you get lots of traffic during lunch time etc.), and the numbers of users during those peak hours. This information can then be used to estimate the number of concurrent users on your site.

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