Which libraries are used to write metrics in Go?

In Go, the most commonly used library for collecting and exporting metrics is Prometheus client_golang, which provides a convenient API for creating counters, histograms, summaries, and other metric types.

Example of usage:

import (
    "github.com/prometheus/client_golang/prometheus"
    "github.com/prometheus/client_golang/prometheus/promhttp"
    "net/http"
)

var (
    opsProcessed = prometheus.NewCounter(prometheus.CounterOpts{
        Name: "myapp_processed_ops_total",
        Help: "The total number of processed events",
    })
)

func init() {
    prometheus.MustRegister(opsProcessed)
}

func handler(w http.ResponseWriter, r *http.Request) {
    opsProcessed.Inc()
    w.Write([]byte("Hello, Metrics!"))
}

func main() {
    http.Handle("/metrics", promhttp.Handler())
    http.HandleFunc("/", handler)
    http.ListenAndServe(":8080", nil)
}

For more complex cases, OpenTelemetry can be used, which supports collecting metrics, traces, and logs, and integrates with Prometheus and other monitoring systems.