Sensu is an open source monitoring tool for ephemeral infrastructure and distributed applications. It is an agent based monitoring system with built-in auto-discovery, making it very well-suited for cloud environments. Sensu uses service checks to monitor service health and collect telemetry data. It also has a number of well defined APIs for configuration, external data input, and to provide access to Sensu's data. Sensu is extremely extensible and is commonly referred to as "the monitoring router".