Add full-observability example: metrics and tracing together

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/full-observability/main.go

@@ -0,0 +1,107 @@
+// Full observability: Prometheus metrics and OpenTelemetry tracing together.
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"math/rand/v2"
+	"net/http"
+	"os"
+	"os/signal"
+	"strconv"
+	"time"
+
+	"git.codelab.vc/pkg/obsx"
+	"go.opentelemetry.io/otel/attribute"
+	"go.opentelemetry.io/otel/codes"
+)
+
+func main() {
+	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt)
+	defer stop()
+
+	// --- Tracing ---
+	shutdown, err := obsx.SetupTracer(ctx, obsx.TracerConfig{
+		ServiceName:    "full-observability",
+		ServiceVersion: "0.1.0",
+		Endpoint:       "localhost:4317",
+	})
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer func() {
+		if err := shutdown(context.Background()); err != nil {
+			log.Printf("tracer shutdown: %v", err)
+		}
+	}()
+
+	// --- Metrics ---
+	metrics := obsx.NewMetrics(obsx.MetricsConfig{
+		Namespace: "myapp",
+		Subsystem: "orders",
+	})
+
+	requests := metrics.Counter("requests_total", "Total requests", "method", "status")
+	duration := metrics.Histogram("request_duration_seconds", "Latency", nil, "method")
+	inflight := metrics.Gauge("inflight_requests", "In-flight requests")
+
+	// --- Routes ---
+	mux := http.NewServeMux()
+
+	mux.HandleFunc("POST /orders", func(w http.ResponseWriter, r *http.Request) {
+		inflight.WithLabelValues().Inc()
+		defer inflight.WithLabelValues().Dec()
+		start := time.Now()
+
+		ctx, span := obsx.StartSpan(r.Context(), "HandleCreateOrder")
+		defer span.End()
+
+		orderID, err := createOrder(ctx)
+
+		status := http.StatusCreated
+		if err != nil {
+			status = http.StatusInternalServerError
+			span.RecordError(err)
+			span.SetStatus(codes.Error, err.Error())
+			http.Error(w, err.Error(), status)
+		} else {
+			span.SetStatus(codes.Ok, "")
+			w.WriteHeader(status)
+			fmt.Fprintf(w, `{"order_id": %q}`+"\n", orderID)
+		}
+
+		requests.WithLabelValues("POST", strconv.Itoa(status)).Inc()
+		duration.WithLabelValues("POST").Observe(time.Since(start).Seconds())
+	})
+
+	mux.Handle("GET /metrics", metrics.Handler())
+
+	// --- Server ---
+	srv := &http.Server{Addr: ":8080", Handler: mux}
+
+	go func() {
+		<-ctx.Done()
+		_ = srv.Shutdown(context.Background())
+	}()
+
+	log.Println("listening on :8080 (try POST /orders, GET /metrics)")
+	if err := srv.ListenAndServe(); err != http.ErrServerClosed {
+		log.Fatal(err)
+	}
+}
+
+// createOrder simulates order creation with a child span.
+func createOrder(ctx context.Context) (string, error) {
+	_, span := obsx.StartSpan(ctx, "db.InsertOrder")
+	defer span.End()
+
+	span.SetAttributes(attribute.String("db.statement", "INSERT INTO orders ..."))
+
+	// Simulate DB latency.
+	time.Sleep(time.Duration(rand.IntN(80)) * time.Millisecond)
+
+	orderID := fmt.Sprintf("ord-%d", rand.IntN(100000))
+	span.SetAttributes(attribute.String("order.id", orderID))
+	return orderID, nil
+}