You are designing an application for use only during business hours. For the minimum viable product release, you'd like to use a managed product that automatically `scales to zero` so you don't incur costs when there is no activity. Which primary compute resource should you choose?

Cloud Functions is the best choice because it is a serverless, event-driven compute platform that automatically scales to zero when not in use, meaning you only pay for the execution time of your code. This directly aligns with the requirement of not incurring costs during off-hours. Compute Engine provides virtual machines, which incur costs even when idle unless manually shut down. Google Kubernetes Engine (GKE) is a managed Kubernetes service that requires running clusters, incurring costs for nodes even with no active workloads. App Engine flexible environment also maintains running instances, leading to costs even during periods of inactivity.