What is this?
Martin Fowler provides a fairly definitive explanation of this (http://martinfowler.com/bliki/BlueGreenDeployment.html) so I’ll try not to regurgitate what he’s written too much! However, in my mind (and in my own words) I’d say that blue green is about 'getting the latest version of your software into production as quickly and efficiently as possible'. Essentially it involves creating a (green) version of your existing (blue) system with your latest code deployment, then (after confirming it works) switching end user requests to use the green version. If there are any issues then you can easily roll back to blue and forget green ever happened.