The correct answer is Spinnaker deployed on GKE, with Jenkins deployed on GKE also being a viable option for facilitating Blue/Green deployments.

• Why Spinnaker and Jenkins? Both tools are designed to support complex deployment strategies, including Blue/Green deployments, which allow for seamless updates and rollbacks.
• Why not the others?
  • Cloud Build is more suited for building and testing rather than deployment strategies.
  • Deployment Manager focuses on infrastructure as code, not application deployment strategies.
  • Cloud Run is a serverless platform that abstracts away the underlying infrastructure, making it unsuitable for direct Blue/Green deployment management.

For further reading, refer to the documentation on Continuous deployment to GKE using Jenkins.