Calvin's dad on load testing

Load testing Facebook applications is really important. Usually the whole point of deploying onto Facebook is to leverage the social graph and go viral. Developers want their applications to go viral, but there’s a nagging concern about what will happen if they do. Is the app as scalable as you think? Are the hosting choices correct? What’s the cost of deploying and crashing?

The way to alleviate these concerns is to load test your app, but how do you do that in a Facebook environment? The simple answer is that it’s very hard due to two issues central to Facebook:

Issue1: You must control enough Facebook users

Testing your application with one or two simultaneous users is easy: simply use your own Facebook account and call up some friends and have them do the same. But running a test with hundreds or even thousands of simultaneous users is much more difficult. Where do you get the users from? That answer isn’t so simple. You can say “I’ll just go into Facebook and define a few hundred ‘phony’ people that I can control”. While this may seem like a good idea, it isn’t:

• It violates the Facebook Terms of Use (section 4.1) which prohibits you from creating phony accounts. When Facebook finds your phony account, they will delete it.
• Real users have friends, become fans of pages, post updates, and hundreds of other things that Facebook allows you to do. This creates the richness of the social graph, and applications often need to take these things into account. Unless you’re willing to spend an inordinate amount of time “humanizing” your phony user army, your tests with them will not be realistic.
• While Facebook does provide the concept of a Test Account to developers to test with, these accounts are very limited in what they can do so are not of very much use for load testing.

Issue 2: Load testing must be automated

Load testing web applications is hard. Traditionally, to test an application you’d deploy it into a “staging area” and then simulate many people using it with a tool such as HP’s LoadRunner or a cloud-based solution such as BrowserMob.

Load testing by it’s very nature must be an automated process. But this is a problem since Facebook applications must be accessed through the Facebook servers (for API support, FBML-to-HTML rendering, etc.)

Load testing the traditional way

This is a problem because it violates Facebook’s Terms of Use (section 3.2) which prohibits the use of accessing the Facebook servers with automated tools. This will force us to rethink our Facebook application load testing strategy.

In Part 2 of article, we’ll discuss why Facebook has a prohibition against automated tools, and why that is ultimately good for you, the developer.