Engineering
Blue-Green Deployment
Blue-green deployment is a release strategy that maintains two identical production environments — one live ("blue") and one idle ("green"). A new version is deployed to the idle environment, tested, and then traffic is switched over to it, leaving the previous environment intact as an instant rollback option.
The main advantage over deploying in place is that rollback is nearly instantaneous: if the new version misbehaves after the switch, traffic is simply redirected back to the still-running previous environment rather than requiring a new deployment to revert.
The trade-off is cost and complexity: running two full production environments simultaneously, even briefly, roughly doubles infrastructure requirements during the deployment window, and stateful systems (databases, in-flight sessions) need careful handling to keep both environments consistent during the switch.