原理：


resolver解析地址，然后获取出 解析后的 resolveConnect;

调用 updateResolveStatus

然后 根据负载均衡 设置，生成负载均衡器；

负载均衡器内负责创建子链接；

子链接创建完后，将子链接传给picker管理，然后更新主链接的状态；

使用步骤：

  1. 定义自己的resolver
  2. resolve出相应的地址，传给负载均衡器builder
  3. 负载均衡器builder创建连接，传给picker

使用方法：

  1. const (
  2.     exampleScheme      = "example"
  3.     exampleServiceName = "lb.example.grpc.io"
  4. )
  6. var addrs = []string{"localhost:50051", "localhost:50052"}
  8. func callUnaryEcho(c ecpb.EchoClient, message string) {
  9.     ctx, cancel := context.WithTimeout(context.Background(), time.Second)
  10.     defer cancel()
  11.     r, err := c.UnaryEcho(ctx, &ecpb.EchoRequest{Message: message})
  12.     if err != nil {
  13.         log.Fatalf("could not greet: %v", err)
  14.     }
  15.     fmt.Println(r.Message)
  16. }
  18. func makeRPCs(cc *grpc.ClientConn, n int) {
  19.     hwc := ecpb.NewEchoClient(cc)
  20.     for i := 0; i < n; i++ {
  21.         callUnaryEcho(hwc, "this is examples/load_balancing")
  22.     }
  23. }
  25. func main() {
  26.     pickfirstConn, err := grpc.Dial(
  27.         fmt.Sprintf("%s:///%s", exampleScheme, exampleServiceName),
  28.         // grpc.WithBalancerName("pick_first"), // "pick_first" is the default, so this DialOption is not necessary.
  29.         grpc.WithInsecure(),
  30.         grpc.WithBlock(),
  31.     )
  32.     if err != nil {
  33.         log.Fatalf("did not connect: %v", err)
  34.     }
  35.     defer pickfirstConn.Close()
  37.     fmt.Println("--- calling helloworld.Greeter/SayHello with pick_first ---")
  38.     makeRPCs(pickfirstConn, 10)
  40.     fmt.Println()
  42.     // Make another ClientConn with round_robin policy.
  43.     roundrobinConn, err := grpc.Dial(
  44.         fmt.Sprintf("%s:///%s", exampleScheme, exampleServiceName),
  45.         grpc.WithBalancerName("round_robin"), // This sets the initial balancing policy.
  46.         grpc.WithInsecure(),
  47.         grpc.WithBlock(),
  48.     )
  49.     if err != nil {
  50.         log.Fatalf("did not connect: %v", err)
  51.     }
  52.     defer roundrobinConn.Close()
  54.     fmt.Println("--- calling helloworld.Greeter/SayHello with round_robin ---")
  55.     makeRPCs(roundrobinConn, 10)
  56. }
  58. // Following is an example name resolver implementation. Read the name
  59. // resolution example to learn more about it.
  61. type exampleResolverBuilder struct{}
  63. func (*exampleResolverBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOptions) (resolver.Resolver, error) {
  64.     r := &exampleResolver{
  65.         target: target,
  66.         cc:     cc,
  67.         addrsStore: map[string][]string{
  68.             exampleServiceName: addrs,
  69.         },
  70.     }
  71.     r.start()
  72.     return r, nil
  73. }
  74. func (*exampleResolverBuilder) Scheme() string { return exampleScheme }
  76. type exampleResolver struct {
  77.     target     resolver.Target
  78.     cc         resolver.ClientConn
  79.     addrsStore map[string][]string
  80. }
  82. func (r *exampleResolver) start() {
  83.     addrStrs := r.addrsStore[r.target.Endpoint]
  84.     addrs := make([]resolver.Address, len(addrStrs))
  85.     for i, s := range addrStrs {
  86.         addrs[i] = resolver.Address{Addr: s}
  87.     }
  88.     r.cc.UpdateState(resolver.State{Addresses: addrs})
  89. }
  90. func (*exampleResolver) ResolveNow(o resolver.ResolveNowOptions) {}
  91. func (*exampleResolver) Close()                                  {}
  93. func init() {
  94.     resolver.Register(&exampleResolverBuilder{})
  95. }