The Prometheus backend · metrics4s · Sendline Open Source

The Prometheus backend

scala

given Metrics[IO] = PrometheusMetrics[IO](registry)              // or PrometheusMetrics[IO](registry, MetricsConfig.default.withPreCreateLimit(1024))
PrometheusMetrics.jvm[IO](registry)                              // the client's own JVM metrics: jvm_memory_used_bytes, process_cpu_seconds_total, ...
PrometheusExporter.allocated[IO](9090, registry).toResource      // HTTPServer; port 0 picks a free one, exporter.port says which
PrometheusScrape.text(registry)                                  // the exposition, for a /metrics route of your own

The registry is passed, never assumed. PrometheusRegistry.defaultRegistry is the one other Java libraries register on, so services often want it. When they do, they write it out.

When the exporter cannot listen on its port, allocated fails with an ExporterException: its message and its port name the port, and the bind failure is its cause.