Kill It with Fire

the blue-green technique involves running two components in parallel and slowly draining traffic off from one and over to the other. The big benefit to doing this is that it’s easy to undo if something goes wrong. Often with technology, increasing load reveals problems that were not otherwise found in testing. Legacy systems have both the blessing and the curse of an existing pool of users and activity. The system that replaces them has a narrow grace period with which to fix those mistakes discovered under high load. Blue-green deployments allow the new system to ease into the full load of the old system gradually, and you can fix problems before the load exacerbates them.