The back-end to GOV.UK is designed to be very configurable by non-technical users, and many of their routes are dynamic. While Puppet could be used, the process of automating those edits, then rolling them out to all the servers, but in batches so that no downtime is experienced with restarts, configuring load balancers to be aware of this, etc, etc, the whole process has lots of points that could fail.
It really sounds like a dynamic front-end that is aware of the routes would be a much better idea, far less that can go wrong.
