Enable an existing GKE cluster to scale automatically with changing demand. What should you do?

The correct option updates an existing GKE cluster to enable autoscaling using the gcloud alpha container clusters update command. This command allows you to modify cluster properties, including enabling and configuring autoscaling with specified minimum and maximum node counts. The alpha command is used because autoscaling features sometimes start in alpha before moving to beta or general availability. Resizing the cluster by adding nodes (gcloud container clusters resize) manually changes the node count but does not enable automatic scaling based on workload demand. Adding an instance tag to enable autoscaling is incorrect because GKE autoscaling is configured at the cluster level, not by individual instance tags. Creating a new cluster with autoscaling and redeploying the application is a valid way to achieve autoscaling, but the question asks how to enable it on an existing cluster, making this option less efficient and potentially disruptive.