The scenario requires a scalable solution for global Prometheus querying across multiple GKE clusters with minimal management overhead. The current Prometheus-based setup lacks global visibility, and manual federation (options A and C) would introduce significant configuration and maintenance complexity, making them unsuitable for minimizing overhead. Option B, configuring workload metrics within Cloud Operations for GKE, leverages Google's managed monitoring but may not fully support Prometheus querying (PromQL) or integrate seamlessly with existing Prometheus-based tooling without additional setup. Option D, configuring Google Cloud Managed Service for Prometheus, is the optimal choice. It is a fully managed service that automatically collects, stores, and aggregates Prometheus metrics from all GKE clusters globally. It supports scalable PromQL querying, integrates with Cloud Operations for dashboards and alerts, and reduces operational burden by handling scaling, reliability, and updates, aligning perfectly with the requirements.