You are deploying a new version of your application using the Blue-Green deployment pattern. What is a characteristic of the Blue-Green deployment pattern?

Blue-Green deployment keeps two identical production environments—“blue” (current) and “green” (new)—running at the same time. The new version is released to the green environment while the blue environment continues to serve users. Once verification is complete, the router or load balancer switches traffic from blue to green in one step, giving an instant rollback path. Therefore, a defining characteristic is that the old and new versions are deployed simultaneously in parallel environments.

A. Implies the old version is removed after the new one is placed; blue-green retains the old version for rollback, so not “new first, then old.”
B. Lists the deployment order but omits the simultaneous coexistence that defines blue-green; thus incomplete and misleading.
D. Contradicts the pattern’s core principle of maintaining two live versions; blue-green never runs a single version only.

1. Humble, J., Farley, D. “Continuous Delivery,” Addison-Wesley, 2010, §11.4 Blue-Green Deployment, pp. 299-300.

2. AWS CodeDeploy User Guide, “Blue/Green Deployments,” Version 2023-11-15, para. 1-2.

3. Kubernetes Documentation, “Deployment Strategies – Blue-Green,” Kubernetes.io, v1.29, Section “Running two production environments.”

4. MIT OpenCourseWare 6.831 “User Interface Design and Implementation,” Lec 24 notes, slide 10: “Blue-Green releases keep old and new sites running concurrently for switch-over.”