snapshot of https://github.com/grpc/grpc-go.git (master, 2026-09-15; blobs > 131072B omitted)

examples/features/load_balancing/client/main.go

@@ -0,0 +1,127 @@
+/*
+ *
+ * Copyright 2018 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.
+ *
+ */
+
+// Binary client demonstrates how to configure load balancing policies to
+// distribute RPCs across backend servers.
+package main
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"time"
+
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/credentials/insecure"
+	ecpb "google.golang.org/grpc/examples/features/proto/echo"
+	"google.golang.org/grpc/resolver"
+)
+
+const (
+	exampleScheme      = "example"
+	exampleServiceName = "lb.example.grpc.io"
+)
+
+var addrs = []string{"localhost:50051", "localhost:50052"}
+
+func callUnaryEcho(c ecpb.EchoClient, message string) {
+	ctx, cancel := context.WithTimeout(context.Background(), time.Second)
+	defer cancel()
+	r, err := c.UnaryEcho(ctx, &ecpb.EchoRequest{Message: message})
+	if err != nil {
+		log.Fatalf("could not greet: %v", err)
+	}
+	fmt.Println(r.Message)
+}
+
+func makeRPCs(cc *grpc.ClientConn, n int) {
+	hwc := ecpb.NewEchoClient(cc)
+	for i := 0; i < n; i++ {
+		callUnaryEcho(hwc, "this is examples/load_balancing")
+	}
+}
+
+func main() {
+	// "pick_first" is the default, so there's no need to set the load balancing policy.
+	pickfirstConn, err := grpc.NewClient(
+		fmt.Sprintf("%s:///%s", exampleScheme, exampleServiceName),
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+	)
+	if err != nil {
+		log.Fatalf("did not connect: %v", err)
+	}
+	defer pickfirstConn.Close()
+
+	fmt.Println("--- calling helloworld.Greeter/SayHello with pick_first ---")
+	makeRPCs(pickfirstConn, 10)
+
+	fmt.Println()
+
+	// Make another ClientConn with round_robin policy.
+	roundrobinConn, err := grpc.NewClient(
+		fmt.Sprintf("%s:///%s", exampleScheme, exampleServiceName),
+		grpc.WithDefaultServiceConfig(`{"loadBalancingConfig": [{"round_robin":{}}]}`), // This sets the initial balancing policy.
+		grpc.WithTransportCredentials(insecure.NewCredentials()),
+	)
+	if err != nil {
+		log.Fatalf("did not connect: %v", err)
+	}
+	defer roundrobinConn.Close()
+
+	fmt.Println("--- calling helloworld.Greeter/SayHello with round_robin ---")
+	makeRPCs(roundrobinConn, 10)
+}
+
+// Following is an example name resolver implementation. Read the name
+// resolution example to learn more about it.
+
+type exampleResolverBuilder struct{}
+
+func (*exampleResolverBuilder) Build(target resolver.Target, cc resolver.ClientConn, _ resolver.BuildOptions) (resolver.Resolver, error) {
+	r := &exampleResolver{
+		target: target,
+		cc:     cc,
+		addrsStore: map[string][]string{
+			exampleServiceName: addrs,
+		},
+	}
+	r.start()
+	return r, nil
+}
+func (*exampleResolverBuilder) Scheme() string { return exampleScheme }
+
+type exampleResolver struct {
+	target     resolver.Target
+	cc         resolver.ClientConn
+	addrsStore map[string][]string
+}
+
+func (r *exampleResolver) start() {
+	addrStrs := r.addrsStore[r.target.Endpoint()]
+	addrs := make([]resolver.Address, len(addrStrs))
+	for i, s := range addrStrs {
+		addrs[i] = resolver.Address{Addr: s}
+	}
+	r.cc.UpdateState(resolver.State{Addresses: addrs})
+}
+func (*exampleResolver) ResolveNow(resolver.ResolveNowOptions) {}
+func (*exampleResolver) Close()                                {}
+
+func init() {
+	resolver.Register(&exampleResolverBuilder{})
+}