中心网关：gateway
四个微服务：user、message、note、relationship

1 中心网关实现服务发现

1.1 设计EtcdDiscovery类

package entity

import (
	"context"
	"fmt"
	clientv3 "go.etcd.io/etcd/client/v3"
	"gonote/gateway/internal/option"
	messageService "gonote/message/service"
	noteService "gonote/note/service"
	relationshipService "gonote/relationship/service"
	userService "gonote/user/service"
	"google.golang.org/grpc"
	"google.golang.org/grpc/credentials/insecure"
	"sync"
	"time"
)

type EtcdDiscovery struct {
	etcdClient *clientv3.Client
	serviceMap map[string]interface{}
	mu         sync.RWMutex
}

func NewEtcdDiscovery(ip string, port int) (*EtcdDiscovery, error) {
	etcdCli, err := clientv3.New(clientv3.Config{
		Endpoints:   []string{fmt.Sprintf("%v:%v", ip, port)},
		DialTimeout: time.Second * 3,
	})
	if err != nil {
		return nil, err
	}
	
	return &EtcdDiscovery{
		etcdClient: etcdCli,
		serviceMap: make(map[string]interface{}),
	}, nil
}

func (ed *EtcdDiscovery) Start(serviceNames []string) {
	for _, serviceName := range serviceNames {
		resp, err := ed.etcdClient.Get(context.TODO(), serviceName)
		if err != nil {
			panic(err)
		}
		addr := string(resp.Kvs[0].Value)

		conn, err := grpc.Dial(addr,
			grpc.WithTransportCredentials(insecure.NewCredentials()))
		if err != nil {
			panic(err)
		}

		// etcd存储的是各个微服务的监听地址，通过监听地址创建服务实例
		switch serviceName {
		case option.User:
			grpcCli := userService.NewUserServiceClient(conn)
			ed.serviceMap[serviceName] = grpcCli
		case option.Relationship:
			grpcCli := relationshipService.NewRelationshipServiceClient(conn)
			ed.serviceMap[serviceName] = grpcCli
		case option.Note:
			grpcCli := noteService.NewNoteServiceClient(conn)
			ed.serviceMap[serviceName] = grpcCli
		case option.Message:
			grpcCli := messageService.NewMessageServiceClient(conn)
			ed.serviceMap[serviceName] = grpcCli
		}
		
		// 开启协程，监听etcd的变化，动态维护各个grpc服务实例
		go ed.watch(serviceName)
	}
}

func (ed *EtcdDiscovery) watch(serviceName string) {
	watchChan := ed.etcdClient.Watch(context.TODO(), serviceName)
	for event := range watchChan {
		for _, e := range event.Events {
			if e.Type == clientv3.EventTypePut {
				addr := string(e.Kv.Value)
				conn, err := grpc.Dial(addr,
					grpc.WithTransportCredentials(insecure.NewCredentials()))
				if err != nil {
					continue
				}
				ed.mu.Lock()
				switch serviceName {
				case option.User:
					grpcCli := userService.NewUserServiceClient(conn)
					ed.serviceMap[serviceName] = grpcCli
				case option.Relationship:
					grpcCli := relationshipService.NewRelationshipServiceClient(conn)
					ed.serviceMap[serviceName] = grpcCli
				case option.Note:
					grpcCli := noteService.NewNoteServiceClient(conn)
					ed.serviceMap[serviceName] = grpcCli
				case option.Message:
					grpcCli := messageService.NewMessageServiceClient(conn)
					ed.serviceMap[serviceName] = grpcCli
				}
				ed.mu.Unlock()
			} else if e.Type == clientv3.EventTypeDelete {
				ed.mu.Lock()
				delete(ed.serviceMap, serviceName)
				ed.mu.Unlock()
			}
		}
	}
}

func (ed *EtcdDiscovery) GetServiceAddr(serviceName string) interface{} {
	ed.mu.RLock()
	defer ed.mu.RUnlock()

	return ed.serviceMap[serviceName]
}

1.2 在web启动时，初始化EtcdDiscovery

package main

import (
	"gonote/gateway/internal"
	"gonote/gateway/internal/option"
	"gonote/gateway/internal/util"
)

func init() {
	util.InitLogger()

	util.InitWebSocketServer(64)

	err := util.InitRedis()
	if err != nil {
		panic(err)
	}

	util.InitKafka(option.Topic)

	util.InitEtcdDiscovery([]string{
		option.User,
		option.Relationship,
		option.Note,
		option.Message})
}

func main() {
	engine := internal.Router()

	if err := engine.Run("0.0.0.0:9090"); err != nil {
		panic(err)
	}
}

1.3 调用EtcdDiscovery获取服务实例

举个用户注册的例子：

func UserLogin(c *gin.Context) {
	em := c.PostForm("email")
	pwd := c.PostForm("pwd")

    // 获取服务实例
	cli := util.EtcdDiscovery.GetServiceAddr(option.User).(service.UserServiceClient)
   
    // 调用服务
	_, err := cli.UserLogin(context.TODO(), &service.User{
		Email: em,
		Pwd:   pwd,
	})

	if err != nil {
		c.JSON(200, gin.H{
			"code": 1,
			"msg":  err.Error(),
		})
		return
	}

	// 生成jwt令牌
	token, err := util.GenToken(em)
	if err != nil {
		c.JSON(200, gin.H{
			"code": 1,
			"msg":  err.Error(),
		})
		return
	}

    // session维护长连接
	session := sessions.Default(c)
	session.Set("email", em)
	err = session.Save()
	if err != nil {
		c.JSON(200, gin.H{
			"code": 1,
			"msg":  err.Error(),
		})
		return
	}

	c.JSON(200, gin.H{
		"code": 0,
		"data": token,
	})
}

2 微服务端进行服务注册

user业务对应的微服务：

func init() {
	util.InitLogger()

	err := util.InitDB()
	if err != nil {
		panic(err)
	}

	util.InitKafka(option.Topic)

	util.InitEtcdCli()
}

func main() {
	addr := option.IP + ":" + option.Port
	ln, err := net.Listen("tcp", addr)
	if err != nil {
		panic(err)
	}
	defer ln.Close()

	defer util.EtcdCli.Close()
	defer util.KafkaCli.Close()

    // 服务注册
	_, err = util.EtcdCli.Put(context.TODO(), "user", addr)
	if err != nil {
		panic(err)
	}

	server := grpc.NewServer()

	service.RegisterUserServiceServer(server, &service.UserServiceImpl{})

	if err = server.Serve(ln); err != nil {
		panic(err)
	}
}

通过etcd命令查看相关注册信息