A company has two identical environments (X and Y) running its core business application. As part of an upgrade, the X environment is patched/upgraded and tested while the Y environment is still servi

A company has two identical environments (X and Y) running its core business application. As part of an upgrade, the X environment is patched/upgraded and tested while the Y environment is still serving the consumer workloads. Upon successful testing of the X environment, all workload is sent to this environment, and the Y environment is then upgraded before both environments start to manage the workloads. Which of the following upgrade methods is being used?