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| package main
import (
"context"
"fmt"
"log"
"time"
"google.golang.org/grpc"
"google.golang.org/grpc/credentials/insecure"
pb "github.com/overstarry/grpc-example/proto/echo"
"google.golang.org/grpc/resolver"
)
const (
exampleScheme = "example"
exampleServiceName = "lb.overstarry.grpc.io"
)
var addrs = []string{"localhost:30051", "localhost:30052", "localhost:30053"}
func callUnaryEcho(c pb.EchoClient, message string) {
ctx, cancel := context.WithTimeout(context.Background(), time.Second)
defer cancel()
r, err := c.UnaryEcho(ctx, &pb.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 := pb.NewEchoClient(cc)
for i := 0; i < n; i++ {
callUnaryEcho(hwc, "this is examples/load_balancing")
}
}
func main() {
pickfirstConn, err := grpc.Dial(
fmt.Sprintf("%s:///%s", exampleScheme, exampleServiceName),
grpc.WithTransportCredentials(insecure.NewCredentials()),
)
if err != nil {
log.Fatalf("did not connect: %v", err)
}
defer pickfirstConn.Close()
makeRPCs(pickfirstConn, 10)
fmt.Println()
roundrobinConn, err := grpc.Dial(
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()
makeRPCs(roundrobinConn, 10)
}
type exampleResolverBuilder struct{}
func (*exampleResolverBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts 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(o resolver.ResolveNowOptions) {}
func (*exampleResolver) Close() {}
func init() {
resolver.Register(&exampleResolverBuilder{})
}
|