When we moved the Twitter web frontend from the RoR stack to the Scala stack we used a similar tool built into the proxy we called Tap Compare. The new thing in Diffy is to use two calls to known good services rather than one call to filter out the non-deterministic bits. With tap compare we basically had to whitelist those parts of the page. This kind of strategy is pretty powerful and you will likely find lots of places in your infrastructure where it makes sense to use it.