You want to test a new app version with production users, route users by operating system, and allow fast rollback if bugs appear. What deployment and traffic-splitting approach should you use?

The correct option leverages Google Kubernetes Engine (GKE) with Anthos Service Mesh because it provides advanced traffic management capabilities, including content-based routing. Anthos Service Mesh allows you to define routing rules based on HTTP headers like the user-agent, which is essential for directing traffic based on the user's operating system. This setup also supports fast rollbacks by adjusting traffic weights. Cloud Run offers traffic splitting but primarily based on percentages or revision tags, not directly on HTTP headers like user-agent for OS-specific routing. App Engine's traffic splitting is also more basic, typically by IP address or cookie, and less granular for header-based routing. Compute Engine with Traffic Director is powerful for service mesh capabilities but doesn't inherently provide the same level of direct, header-based traffic splitting as Anthos Service Mesh for this specific use case without additional configuration.