Deployment strategy using two identical environments where you switch traffic from old version to new version instantly. Like having two identical stages where you prepare the new show while the old one is running.
You deploy the new version to the 'green' environment, test it thoroughly, then instantly switch all users from 'blue' to 'green' with zero downtime.
All providers support blue-green by running two production-like environments and shifting traffic using a load balancer, DNS, or a platform feature (e.g., App Service slots). AWS has explicit blue/green support in CodeDeploy; Azure commonly uses App Service slot swaps; GCP commonly implements it on GKE by switching Service selectors/Ingress backends; OCI typically combines OCI DevOps pipelines with OCI Load Balancer routing changes.