$ show nats-io/prometheus-nats-exporter
This is a Prometheus exporter for NATS server monitoring. It polls NATS server HTTP monitoring endpoints (varz, connz, subz, routez, healthz, jsz, etc.) and exposes metrics in Prometheus format. The architecture is a standalone binary with an embeddable library API. Key entry points are the CLI (main.go) and the exporter.NewExporter function. Data flow: on each scrape, collectors make HTTP requests to NATS monitoring endpoints, parse JSON responses, and convert them to Prometheus gauge metrics. The exporter supports TLS, basic auth, custom metric prefixes, and multiple NATS servers (though one per exporter is recommended). It includes pre-built Grafana dashboards for both NATS core and JetStream metrics. The codebase is well-structured with separate packages for collectors, exporter, and test utilities. It uses reflection-based metric extraction for simple endpoints and custom collectors for complex ones like JetStream, connections, and gateways. The project is actively maintained with recent commits and modern dependencies.
The LLM identified 2 files worth highlighting for reuse:
Custom collector for the NATS connz endpoint. Implements a custom UnmarshalJSON for ConnzConnection that handles NATS-specific time and duration formats (e.g., '1d2h3m4s' for uptime). The parseDuration function is a reusable utility for converting NATS duration strings (with years, days, hours, minutes, seconds) to milliseconds. This pattern is necessary because Go's time.ParseDuration cannot handle day/year units. The collector also supports detailed per-connection metrics with rich label sets including TLS info, account, and client metadata.
Base collector with reflection-based metric extraction. The objectToMetrics method recursively flattens JSON response fields into Prometheus gauge metrics, automatically handling nested objects and string values (with time parsing for RFC3339 timestamps). The mapKeys function provides schema drift detection by tracking all response keys across polls; if the NATS server changes its JSON shape, collectors are re-initialized rather than silently dropping new fields. This pattern is reusable for any Prometheus exporter that needs to dynamically adapt to evolving JSON APIs.