Codevault initial commit

internal/observability/metrics/configure.go

@@ -0,0 +1,83 @@
+package metrics
+
+import (
+	"context"
+	"fmt"
+	"net"
+	"net/http"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"go.opentelemetry.io/otel"
+	"go.opentelemetry.io/otel/exporters/prometheus"
+	otelmetric "go.opentelemetry.io/otel/metric"
+	"go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/resource"
+
+	"github.com/kanootoko/codevault/internal"
+	"github.com/kanootoko/codevault/internal/config"
+	"github.com/kanootoko/codevault/internal/observability"
+	"github.com/kanootoko/codevault/internal/utils/gshutdown"
+)
+
+// Configure starts a Prometheus server which serves metrics and finishes on context finish
+func Configure(ctx context.Context, cfg config.MetricsConfig) error {
+	if cfg.Host == "" {
+		return nil
+	}
+	res, err := observability.GetOtelResource()
+	if err != nil {
+		return fmt.Errorf("cannot get OpenTelemetry resource: %w", err)
+	}
+
+	meterProvider, err := newMeterProvider(res)
+	if err != nil {
+		return fmt.Errorf("cannot instanciate OpenTelemetry meter provider: %w", err)
+	}
+
+	otel.SetMeterProvider(meterProvider)
+
+	mux := http.NewServeMux()
+	mux.Handle("/metrics", promhttp.Handler())
+	server := http.Server{
+		Addr:              fmt.Sprintf(":%d", cfg.Port),
+		Handler:           mux,
+		ReadTimeout:       time.Second * 20,
+		ReadHeaderTimeout: time.Second * 10,
+		WriteTimeout:      time.Second * 20,
+	}
+	listener, err := net.Listen("tcp", fmt.Sprintf("%s:%d", cfg.Host, cfg.Port))
+	if err != nil {
+		return fmt.Errorf("error on creating listener for prometheus metrics: %w", err)
+	}
+	go func() { _ = server.Serve(listener) }()
+	_ = gshutdown.SubtaskStarted(ctx, "prometheus")
+	go func() {
+		defer func() {
+			_ = listener.Close()
+			_ = gshutdown.SubtaskFinished(ctx, "prometheus")
+		}()
+		<-ctx.Done()
+		_ = server.Shutdown(context.Background())
+	}()
+
+	return nil
+}
+
+func GetMeter() otelmetric.Meter {
+	mp := otel.GetMeterProvider()
+	return mp.Meter(internal.PackageName, otelmetric.WithInstrumentationVersion(internal.Version))
+}
+
+func newMeterProvider(res *resource.Resource) (*metric.MeterProvider, error) {
+	metricExporter, err := prometheus.New()
+	if err != nil {
+		return nil, err
+	}
+
+	meterProvider := metric.NewMeterProvider(
+		metric.WithResource(res),
+		metric.WithReader(metricExporter),
+	)
+	return meterProvider, nil
+}