Metrics Endpoint

The API exposes a Prometheus-compatible metrics endpoint at GET /metrics when enabled.

See Evironment Variables

Enabling Metrics

export METRICS_ENABLED=true

Accessing Metrics

curl http://localhost:3000/metrics

Prometheus Format

The endpoint returns metrics in Prometheus text format. Both default Node.js/fastify metrics and custom application metrics are exposed.

Custom Application Metrics

Metric	Type	Labels	Description
tls_check_total	Counter	status, valid	Total TLS/SSL certificate checks performed
tls_check_duration_seconds_total	Counter	-	Total time spent performing TLS checks
revocation_check_total	Counter	status, source	Total revocation checks performed
http_response_status_total	Counter	status_code, route	HTTP responses by status code and route

Labels

• tls_check_total: status (success/error), valid (true/false)
• revocation_check_total: status (good/revoked/unknown/error), source (ocsp/crl)
• http_response_status_total: status_code (200/400/429/502), route (/api/check)

Default Metrics

fastify-metrics also exposes standard Node.js and Fastify metrics:

Metric	Description
process_cpu_seconds_total	CPU time spent
process_resident_memory_bytes	Memory usage
nodejs_eventloop_lag_seconds	Event loop lag
nodejs_gc_duration_seconds	Garbage collection time
http_request_duration_seconds	Request duration histogram
http_request_summary_seconds	Request duration summary

Prometheus Configuration

Add to your prometheus.yml:

scrape_configs:
  - job_name: 'tlscheck-api'
    static_configs:
      - targets: ['api:3000']

Grafana Dashboards

Import the Node.js / Prometheus dashboard for additional visualizations.