Overview
Metrics are quantitative measurements of the server's operation, resource use, and workload. They let administrators see how the server behaves over time, spot trends, and react to anomalies. Metric collection in Stalwart is controlled by the Metrics singleton (found in the WebUI under Settings › Telemetry › Metrics › General, Settings › Telemetry › Metrics › OpenTelemetry, Settings › Telemetry › Metrics › Prometheus).
OpenTelemetry
OpenTelemetry is an open-source observability framework that standardises how metrics, logs, and traces are collected, processed, and exported. It defines a common wire format for telemetry data and provides SDKs and collector services for a wide range of programming languages and platforms.
Prometheus
Prometheus is an open-source monitoring and alerting toolkit developed originally at SoundCloud and now part of the Cloud Native Computing Foundation. It uses a time-series data model, a dedicated query language (PromQL), and a pull-based scraping model where the server collects metrics from each monitored target at regular intervals.