Prometheus

Prometheus is an open-source systems monitoring and alerting toolkit originally built at SoundCloud and now a graduated project of the Cloud Native Computing Foundation (CNCF). It has become the de facto standard for infrastructure monitoring in modern hosting and cloud environments, particularly alongside Grafana for visualization.

The architecture is built around a pull-based model where the Prometheus server scrapes metrics from instrumented targets at configured intervals. Targets expose metrics via HTTP endpoints in a simple text format, making it easy to instrument any application or service. Thousands of exporters exist for common services: node_exporter for Linux system metrics, mysqld_exporter for MySQL/MariaDB, postgres_exporter for PostgreSQL, apache_exporter, nginx_exporter, and many more.

PromQL (Prometheus Query Language) is the powerful query language for selecting, aggregating, and transforming time-series data. It supports mathematical operations, aggregations, rate calculations, histograms, and prediction functions. PromQL is what makes Prometheus dashboards in Grafana so flexible and informative.

For hosting providers, Prometheus provides comprehensive infrastructure monitoring: CPU usage, memory consumption, disk I/O, network traffic, service availability, and application-specific metrics across all servers. The alerting system (Alertmanager) handles deduplication, grouping, silencing, and routing of alerts to email, Slack, PagerDuty, or webhooks.

Prometheus stores data in a custom time-series database optimized for write-heavy workloads and fast querying. Default retention is 15 days, but this is configurable. For long-term storage, Prometheus supports remote write to solutions like Thanos, Cortex, or VictoriaMetrics, which provide horizontal scaling and extended retention.

The combination of Prometheus for data collection and alerting with Grafana for visualization has become the standard monitoring stack in the hosting industry, often replacing older solutions like Nagios and Cacti.