Yeah good point. We actually run kage proxy behind another load balancer, and only send traffic with a sampling cookie set, which can be controlled from our main app.
This is freaking awesome, I'll be upgrading quite a big busy complex site to a new code version and this should help a lot with testing. Shame that it doesn't support SSL yet, but we can't be picky!
Good concept. But this design is insane. The shadow should be attached via a logging plugin to your trusted webserver or load balancer, so it doesn't destabilize your production system.
Well, I take "insane" as a compliment :) While it is true you can emulate the traffic by looking at web server logs, it was crucial for us to send the exact same request including the same HTTP headers and request body (think POST requests), in real time with the same access pattern.
It was easier for us to write EM based proxy like this than writing a web server plugin that does it, etc.
Another solution using only netcat and tee is described on ServerFault: http://serverfault.com/questions/309583/duplicate-incoming-t...