What is Blue/Green?

Blue/Green deployment is a deployment strategy that reduces downtime and risk by running two identical production environments called "Blue" and "Green". At any time, only one environment is live, serving all production traffic. For example, Blue may be live, and Green is idle. A change is prepared in the Green environment, and once fully tested and ready, traffic is switched from Blue to Green. Blue then becomes the idle environment, ready for the next update. This allows for rapid rollback if issues arise after the switch, simply by reverting traffic back to the Blue environment.