feat: OpenTelemetry tracing and metrics (#262) (#495)

Co-authored-by: ItalyPaleAle <43508+ItalyPaleAle@users.noreply.github.com>

backend/internal/bootstrap/otel_boostrap.go

@@ -0,0 +1,107 @@
+package bootstrap
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/pocket-id/pocket-id/backend/internal/common"
+	"github.com/pocket-id/pocket-id/backend/internal/utils"
+	"go.opentelemetry.io/contrib/exporters/autoexport"
+	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
+	"go.opentelemetry.io/otel"
+	metricnoop "go.opentelemetry.io/otel/metric/noop"
+	"go.opentelemetry.io/otel/propagation"
+	"go.opentelemetry.io/otel/sdk/metric"
+	"go.opentelemetry.io/otel/sdk/resource"
+	sdktrace "go.opentelemetry.io/otel/sdk/trace"
+	semconv "go.opentelemetry.io/otel/semconv/v1.30.0"
+	tracenoop "go.opentelemetry.io/otel/trace/noop"
+)
+
+func defaultResource() (*resource.Resource, error) {
+	return resource.Merge(
+		resource.Default(),
+		resource.NewSchemaless(
+			semconv.ServiceName("pocket-id-backend"),
+			semconv.ServiceVersion(common.Version),
+		),
+	)
+}
+
+func initOtel(ctx context.Context, metrics, traces bool) (shutdownFns []utils.Service, httpClient *http.Client, err error) {
+	resource, err := defaultResource()
+	if err != nil {
+		return nil, nil, fmt.Errorf("failed to create OpenTelemetry resource: %w", err)
+	}
+
+	shutdownFns = make([]utils.Service, 0, 2)
+
+	httpClient = &http.Client{}
+	defaultTransport, ok := http.DefaultTransport.(*http.Transport)
+	if !ok {
+		// Indicates a development-time error
+		panic("Default transport is not of type *http.Transport")
+	}
+	httpClient.Transport = defaultTransport.Clone()
+
+	if traces {
+		tr, err := autoexport.NewSpanExporter(ctx)
+		if err != nil {
+			return nil, nil, fmt.Errorf("failed to initialize OpenTelemetry span exporter: %w", err)
+		}
+		tp := sdktrace.NewTracerProvider(
+			sdktrace.WithResource(resource),
+			sdktrace.WithBatcher(tr),
+		)
+
+		otel.SetTracerProvider(tp)
+		otel.SetTextMapPropagator(
+			propagation.NewCompositeTextMapPropagator(
+				propagation.TraceContext{},
+				propagation.Baggage{},
+			),
+		)
+
+		shutdownFns = append(shutdownFns, func(shutdownCtx context.Context) error { //nolint:contextcheck
+			tpCtx, tpCancel := context.WithTimeout(shutdownCtx, 10*time.Second)
+			defer tpCancel()
+			shutdownErr := tp.Shutdown(tpCtx)
+			if shutdownErr != nil {
+				return fmt.Errorf("failed to gracefully shut down traces exporter: %w", shutdownErr)
+			}
+			return nil
+		})
+
+		httpClient.Transport = otelhttp.NewTransport(httpClient.Transport)
+	} else {
+		otel.SetTracerProvider(tracenoop.NewTracerProvider())
+	}
+
+	if metrics {
+		mr, err := autoexport.NewMetricReader(ctx)
+		if err != nil {
+			return nil, nil, fmt.Errorf("failed to initialize OpenTelemetry metric reader: %w", err)
+		}
+		mp := metric.NewMeterProvider(
+			metric.WithResource(resource),
+			metric.WithReader(mr),
+		)
+
+		otel.SetMeterProvider(mp)
+		shutdownFns = append(shutdownFns, func(shutdownCtx context.Context) error { //nolint:contextcheck
+			mpCtx, mpCancel := context.WithTimeout(shutdownCtx, 10*time.Second)
+			defer mpCancel()
+			shutdownErr := mp.Shutdown(mpCtx)
+			if shutdownErr != nil {
+				return fmt.Errorf("failed to gracefully shut down metrics exporter: %w", shutdownErr)
+			}
+			return nil
+		})
+	} else {
+		otel.SetMeterProvider(metricnoop.NewMeterProvider())
+	}
+
+	return shutdownFns, httpClient, nil
+}