Tier-1 for CMS was created in JINR in 2015. It is important to keep an eye on the Tier-1 center all the time in order to maintain its performance. The one monitoring system is based on Nagios: it monitors the center on the several levels: engineering infrastructure, network and hardware. It collects many metrics, creates plots and determines some statuses like HDD state, temperatures, loads and many other. But this information is not always enough to tell if the sTier services are working properly. For that purpose the service monitoring system was developed in order to collect data from different resources including WLCG monitoring services. The purpose of this system is to aggregate data from different sources, determine statuses based on new and historical date and react according to some predefined instructions. The systems, general idea and architecture are described and analyzed in this work.