We used Optimizely (https://www.optimizely.com/ https://www.optimizely.com/) to conduct most of our a/b testing. Optimizely works on the client level (browser),

We used Optimizely (https://www.optimizely.com/ https://www.optimizely.com/) to conduct most of our a/b testing. Optimizely works on the client level (browser), not the server level (CDN). Optimizely is the best a/b testing software I've ever used. It's flexible and easy to use. I suggest you check it out.