Fronting Apache with Nginx

I’ve been exploring using Nginx to front our Apache websites. I found a fair amount of documentation online but most of it was for nginx on top of a backend application running on the same host – so, lots of examples of load balancing among various ports on 127.0.0.1. In my case I have name-based Apache virtual hosts running at different IP addresses. Also my goal is not to set up automatic load balancing – our session-based application will not work well with it – but rather I want to be able to rapidly and manually switch a web address to a different machine so I can perform maintenance on or updates to the offline systems.

To summarise, I want the publically accessible crashingdaily.com website to be a proxy server to our internal, Apache name-based virtual hosts w1 or w2. I want to be able to choose which of w1 or w2 services the client’s request.