CI/CD pipeline builds and pushes container on tag; final step must deploy to production GKE with zero downtime, automated testing before rollout, and fast rollback. Which tool and strategy do you choose?

The question asks for a deployment strategy that includes zero downtime, automated testing before rollout, and fast rollback. A shadow test (also known as shadow deployment or dark launch) sends a copy of production traffic to the new version of the application without impacting live users. This allows for real-time testing and performance validation in a production-like environment before any actual user traffic is routed. If issues arise, the new version can be discarded without affecting users, ensuring zero downtime and fast rollback. Using Cloud Build with Kubernetes CLI tools provides the necessary automation and control for this process. Canary and A/B tests involve routing a small percentage of live user traffic to the new version, which introduces some risk. While useful, they don't fully meet the "automated testing before rollout" aspect as directly as shadow testing, which tests with production traffic without impacting users.