Question

Anyone can point out the difference between virtual user and real user?

Answer 1

In the context of web load testing, there are a lot of differences. A virtual user is a simulation of human using a browser to perform some actions on a website. One company offers what they call “real browser users”, but they, too, are simulations – just at a different layer (browser vs HTTP). I’m going to assume you are using “real users” to refer to humans.

Using humans to conduct a load test has a few advantages, but is fraught with difficulties. The primary advantage is that there are real humans using real browsers – which means that, if they are following the scripts precisely, there is virtually no difference between a simulation and real traffic. The list of difficulties, however, is long: First, it is expensive. The process does not scale well beyond a few dozen users in a limited number of locations. Humans may not follow the script precisely…and you may not be able to tell if they did. The test is likely not perfectly repeatable. It is difficult to collect, integrate and analyze metrics from real browsers. I could go on…

Testing tools which use virtual users to simulate real users do not have any of those disadvantages – as they are engineered for this task. However, depending on the tool, they may not perform a perfect simulation. Most load testing tools work at the HTTP layer – simulating the HTTP messages passed between the browser and server. If the simulation of these messages is perfect, then the server cannot tell the difference between real and simulated users…and thus the test results are more valid. The more complex the application is, particularly in the use of javascript/AJAX, the harder it is to make a perfect simulation. The capabilities of tools in this regard varies widely.

There is a small group of testing tools that actually run real browsers and simulate the user by pushing simulated mouse and keyboard events to the browser. These tools are more likely to simulate the HTTP messages perfectly, but they have their own set of problems. Most are limited to working with only a single browser (i.e. Firefox). It can be hard to get good metrics out of real browsers. This approach is far more scalable better than using humans, but not nearly as scalable as HTTP-layer simulation. For sites that need to test <10k users, though, the web-based solutions using this approach can provide the required capacity.