Today’s digital society implies interconnectivity between the online operations of different sectors of everyday life and economy alike. As a consequence, malicious activities targeted towards a single online service could hurt entire indus¬tries and multiple private and public organizations. This interdependence be¬tween online services and economic units is an imperative for targeted efforts ensuring the integrity and availability of individual systems and complex systems-of-systems alike. This article presents MonSys, a flexible, robust, and scalable monitoring platform, implement-ed as a cloud-based service and an on-premise solution, specifically de-signed to ad¬dress the need for ensuring service availability at an individual level. MonSys provides several standardized services availability checks, such as web-based services from multiple geographical locations, and a flexible platform and tools for defining customized complex services. Particular attention is paid to the processes of metrics collection, processing, storage, and querying. MonSys can perform custom availability checks for different types of infrastructures, such as various black-box, grey-box, and white-box availability checks/metrics. The article presents also results from piloting the platform on performance and scalability and options for integration in early-warning and intelligent signaling, based on behavioral pattern analysis and predictive simulations.