Using the Prometheus blackbox exporter to monitor modern web infrastructure

Prometheus is a monitoring system that collects time series metrics from targets at regular intervals. Those metrics are stored with labels, queried with PromQL (Prometheus's custom query language), and graphed in tools like Grafana. In a typical setup, Prometheus scrapes metrics from exporters running beside the systems you care about: a node exporter that exports system metrics like CPU, memory and network utilization, a postgresql exporter that makes pg_stat* data available, or an application endpoint that exposes custom metrics. That model is powerful, but it mostly answers questions from inside the system…