Distributed monitoring is an essential functionality to allow large cluster federations to efficiently schedule applications on a set of available geo-distributed resources. However, periodically reporting the precise status of each available server is both unnecessary to allow accurate scheduling and unscalable when the number of servers grows. This paper proposes Acala, an aggregate monitoring framework for geo-distributed Kubernetes cluster federations which aims to provide the management cluster with aggregated information about the entire cluster instead of individual servers. Based on actual deployment under a controlled environment in the geo-distributed Grid'5000 testbed, our evaluations show that Acala reduces the cross-cluster network traffic by up to 97% and the scrape duration by up to 55% in the single member cluster experiment. Our solution also decreases cross-cluster network traffic by 95% and memory resource consumption by 83% in multiple member cluster scenarios. A comparison of scheduling efficiency with and without data aggregation shows that aggregation has minimal effects on the system's scheduling function. These results indicate that our approach is superior to the existing solution and is suitable to handle large-scale geo-distributed Kubernetes cluster federation environments.