Prometheus is an open source monitoring system and time series database. It addresses many aspects of monitoring such as the generation and collection of metrics, graphing the resulting data on dashboards, and alerting on anomalies. To achieve this, it offers a variety of components that are run separately but used in combination.
Docker provides a way for you to encapsulate server processes using Linux containers (or other encapsulation technologies) so that they are more easily managed and isolated from each other.