examples: Add OpenTelemetry example (#7296)

examples/features/opentelemetry/README.md

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+# OpenTelemetry
+
+This example shows how to configure OpenTelemetry on a client and server, and shows
+what type of telemetry data it can produce for certain RPC's.
+
+## Try it
+
+```
+go run server/main.go
+```
+
+```
+go run client/main.go
+```
+
+```
+curl localhost:9464/metrics
+curl localhost:9465/metrics
+```
+
+## Explanation
+
+The client continuously makes RPC's to a server. The client and server both
+expose a prometheus exporter to listen and provide metrics. This defaults to
+:9464 for the server and :9465 for the client.
+
+OpenTelemetry is configured on both the client and the server, and exports to
+the Prometheus exporter. The exporter exposes metrics on the Prometheus ports
+described above.
+
+Curling to the exposed Prometheus ports outputs the metrics recorded on the
+client and server.

examples/features/opentelemetry/client/main.go

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+/*
+ *
+ * Copyright 2024 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+	"google.golang.org/grpc/examples/features/proto/echo"
+	"google.golang.org/grpc/stats/opentelemetry"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"go.opentelemetry.io/otel/exporters/prometheus"
+	"go.opentelemetry.io/otel/sdk/metric"
+)
+
+var (
+	addr               = flag.String("addr", ":50051", "the server address to connect to")
+	prometheusEndpoint = flag.String("prometheus_endpoint", ":9465", "the Prometheus exporter endpoint")
+)
+
+func main() {
+	exporter, err := prometheus.New()
+	if err != nil {
+		log.Fatalf("Failed to start prometheus exporter: %v", err)
+	}
+	provider := metric.NewMeterProvider(metric.WithReader(exporter))
+	go http.ListenAndServe(*prometheusEndpoint, promhttp.Handler())
+
+	ctx := context.Background()
+	do := opentelemetry.DialOption(opentelemetry.Options{MetricsOptions: opentelemetry.MetricsOptions{MeterProvider: provider}})
+
+	cc, err := grpc.NewClient(*addr, grpc.WithTransportCredentials(insecure.NewCredentials()), do)
+	if err != nil {
+		log.Fatalf("Failed to start NewClient: %v", err)
+	}
+	defer cc.Close()
+	c := echo.NewEchoClient(cc)
+
+	// Make a RPC every second. This should trigger telemetry to be emitted from
+	// the client and the server.
+	for {
+		r, err := c.UnaryEcho(ctx, &echo.EchoRequest{Message: "this is examples/opentelemetry"})
+		if err != nil {
+			log.Fatalf("UnaryEcho failed: %v", err)
+		}
+		fmt.Println(r)
+		time.Sleep(time.Second)
+	}
+}

examples/features/opentelemetry/server/main.go

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+/*
+ *
+ * Copyright 2024 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+
+	"google.golang.org/grpc"
+	pb "google.golang.org/grpc/examples/features/proto/echo"
+	"google.golang.org/grpc/stats/opentelemetry"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	"go.opentelemetry.io/otel/exporters/prometheus"
+	"go.opentelemetry.io/otel/sdk/metric"
+)
+
+var (
+	addr               = flag.String("addr", ":50051", "the server address to connect to")
+	prometheusEndpoint = flag.String("prometheus_endpoint", ":9464", "the Prometheus exporter endpoint")
+)
+
+type echoServer struct {
+	pb.UnimplementedEchoServer
+	addr string
+}
+
+func (s *echoServer) UnaryEcho(ctx context.Context, req *pb.EchoRequest) (*pb.EchoResponse, error) {
+	return &pb.EchoResponse{Message: fmt.Sprintf("%s (from %s)", req.Message, s.addr)}, nil
+}
+
+func main() {
+	exporter, err := prometheus.New()
+	if err != nil {
+		log.Fatalf("Failed to start prometheus exporter: %v", err)
+	}
+	provider := metric.NewMeterProvider(metric.WithReader(exporter))
+	go http.ListenAndServe(*prometheusEndpoint, promhttp.Handler())
+
+	so := opentelemetry.ServerOption(opentelemetry.Options{MetricsOptions: opentelemetry.MetricsOptions{MeterProvider: provider}})
+
+	lis, err := net.Listen("tcp", *addr)
+	if err != nil {
+		log.Fatalf("Failed to listen: %v", err)
+	}
+	s := grpc.NewServer(so)
+	pb.RegisterEchoServer(s, &echoServer{addr: *addr})
+
+	log.Printf("Serving on %s\n", *addr)
+
+	if err := s.Serve(lis); err != nil {
+		log.Fatalf("Failed to serve: %v", err)
+	}
+}