Set up A/B testing using Cloudflare workers

If you’ve ever worked on a B2C web application, chances are you’ve encountered A/B testing. My first experience with A/B testing was back in 2011 at Yahoo!. Every new widget on the search page underwent A/B testing, with Yahoo! having its own setup for conducting these tests. However, in subsequent roles at different organizations, I noticed varying approaches to A/B testing, often limited to frontend modifications resulting in UI flickers.

Fast forward to this date. I use Cloudflare at work. Cloudflare offers a serverless feature known as “Workers,” which can be leveraged for A/B testing. The concept is straightforward:

• Divide incoming traffic into buckets
• Set a cookie, let us call this abcookie, for each bucket
• Pass this cookie with every request to and from your application
• Implement the necessary actions in your application based on these cookies
• …
• Achieve success!

Now, in Cloudflare workers:

• Intercept every request
• Check for the abcookie
• If the cookie was found, pass the request to origin
• If the cookie wasn’t found, create abcookie with its value to a test variant
• Ensure the cookie is sent to origin for you to do your thing and to client for them to return it
• That’s all