Staging / AB Testing CDN Hosting Javascript

Question

Let's assume that i have a single javascript file that I have handed out to a lot of my clients, similar to GA's *ga.js, and this file is getting loaded high enough number of times that I have to host it on a CDN.

The problem I have with this setup is that it makes it really hard to 'stage' a new version of javascript. Ideally, when I have a new version of the JS, I would like to split the incoming traffic to the CDN, and send 1% of the entire traffic to the new JS (randomly chosen), or possibly send the new JS only to specific URLs.

I have come across this issue multiple times and have not come up with a good solution. One possible solution is working with the CDN, though it is a long process. Alternative solution is having the customers always load a bootstrapper javascript, which knows where the actual JS or the staged JS lives and splits traffic accordingly.

I am curious if there is alternative solutions people have come up with. This is common enough problem for any company that distributes their JS like, Google, Twitter, Facebook, Linkedin, etc.

Lightness

I think your best bet is the bootstrapper Javascript, since it allows you to maintain control from your end. – Speedy

Answer 1

Since most of CDN services rely on you adding a new CNAME record to your domain to point to CDN hostname. You can use DNS to split a traffic between different CDN services.

1. Round-robin_DNS - splits trafffic more or less evenly
2. geo-load-balancing - allows to set a mapping to specific host based on user location.

Gaza

Could definitely be a possibility, but the TTL on our DNS cache is fairly large, so it would take a long time to get the staging setup ready. Furthermore, relying on DNS propagation would be a headache. Finally, getting the 99%/1% split using round-robin would require 100 entries in the DNS file, which could get unwieldy :) – Lightness