用consul做grpc的服务发现与健康检查consul服务发现与负载均衡当server端是集群部署时，client调用server就需要用到服务发现与负载均衡。通常有两总方式：一种方式是在client与server之间加代理，由代理来做负载均衡一种方式是将服务注册到一个数据中心，client通过数据中心查询到所有服务的节点信息，然后自己选择负载均衡的策略。第一种方式常见的就是用nginx给http服务做负载均衡，client端不直接与server交互，而是把请求并给nginx，nginx再转给后端的服务。这种方式的优点是：client和server无需做改造，client看不到server的集群，就像单点一样调用就可以这种方式有几个缺点：所有的请求都必须经过代理，代理侧容易出现性能瓶颈代理不能出故障，一旦代理挂了服务就没法访问了。第二种方式可以参考dubbo的rpc方式，所有的服务都注册在zookeeper上，client端从zookeeper订阅server的列表，然后自己选择把请求发送到哪个server上。对于上面提到的两个缺点，这种方式都很好的避免了：client与server端是直接交互的，server可以做任意的水平扩展，不会出现性能瓶颈注册中心(zookeeper)通过raft算法实现分布式高可用，不用担心注册中心挂了服务信息丢失的情况。这种方式的缺点就是实现起来比较复杂。用第一种方式做grpc的负载均衡时可以有以下的选择：nginx grpctraefik grpc用第二种方式时，可以选择的数据中心中间件有:zookeeperetcd Etcd是Kubernetes集群中的一个十分重要的组件consul他们都实现了raft算法，都可以用来做注册中心，本篇文章选择consul是因为consul的特点就是做服务发现，有现成的api可以用。用consul给golang的grpc做服务注册与发现grpc的resolvergrpc的Dial()和DialContent()方法中都可以添加Load-Balance的选项，Dial方法已经被废弃了，本篇文章介绍使用DialContext的方法。grpc官方实现了dns_resolver用来做dns的负载均衡。我们通过例子看看grpc client端的代码是怎么写的，然后再理解dns_resolver的源码，最后参照dns_resolver来写自己的consul_resovler。dns的负载均衡的例子:package mainimport ( “context” “log” “google.golang.org/grpc” “google.golang.org/grpc/balancer/roundrobin” pb “google.golang.org/grpc/examples/helloworld/helloworld” “google.golang.org/grpc/resolver”)const ( address = “dns:///dns-record-name:443” defaultName = “world”)func main() { // The secret sauce resolver.SetDefaultScheme(“dns”) // Set up a connection to the server. ctx, _ := context.WithTimeout(context.Background(), 5*time.Second) conn, err := grpc.DialContext(ctx, address, grpc.WithInsecure(), grpc.WithBalancerName(roundrobin.Name)) if err != nil { log.Fatalf(“did not connect: %v”, err) } defer conn.Close() c := pb.NewGreeterClient(conn) // Contact the servers in round-robin manner. for i := 0; i < 3; i++ { ctx := context.Background() r, err := c.SayHello(ctx, &pb.HelloRequest{Name: defaultName}) if err != nil { log.Fatalf(“could not greet: %v”, err) } log.Printf(“Greeting: %s”, r.Message) }}DialContext的定义如下:func DialContext(ctx context.Context, target string, opts …DialOption) (conn *ClientConn, err error)下面这行代码指明了用dns_resolver，实际上也可以不写，grpc会根据DialContext的第二个参数target来判断选用哪个resolver，例子中传给DialContext的target是 dns:///dns-record-name:443，grpc会自动选择dns_resolverresolver.SetDefaultScheme(“dns”)下面的这个选项，指明了grpc用轮询做为负载均衡的策略grpc.WithBalancerName(roundrobin.Name)调用grpc.DialContext之后，grpc会找到对应的resovler，拿到服务的地址列表，然后在调用服务提供的接口时，根据指定的轮询策略选择一个服务。gRPC Name Resolution里面说了，可以实现自定义的resolver作为插件。先看看resolver.go的源码，源码路径是$GOPATH/src/google.golang.org/grpc/resolver/resolver.gom = make(map[string]Builder) //scheme到Builder的mapfunc Register(b Builder) { //用于resolver注册的接口，dns_resolver.go的init方中调用了这个方法,实际就是更新了map m[b.Scheme()] = b}type Resolver interface { ResolveNow(ResolveNowOption) //立即resolve，重新查询服务信息 Close() //关闭这个Resolver}type Target struct {//uri解析之后的对象, uri的格式详见RFC3986 Scheme string Authority string Endpoint string}type Address struct {//描述一个服务的地址信息 Addr string //格式是 host:port Type AddressType ServerName string Metadata interface{}}type ClientConn interface {//定义了两个callback函数，用于通知服务信息的更新 NewAddress(addresses []Address) NewServiceConfig(serviceConfig string)}type Builder interface { Build(target Target, cc ClientConn, opts BuildOption) (Resolver, error) //返回一个Resolver Scheme() string //返回scheme如 “dns”, “passthrough”, “consul”}func Get(scheme string) Builder { //grpc.ClientConn会高用这个方法获取指定的Builder接口的实例 if b, ok := m[scheme]; ok { return b } return nil}即使加了注释，估计也很难马上理解这个其中的具体含意，博主也是结合dns_resolver.go，反复读了好几遍才理解resolver.go。其大致的意思是，grpc.DialContext方法调用之后：解析target(例如dns:///dns-record-name:443)获取scheme调用resolver.Get方法根据scheme拿到对应的Builder调用Builder.Build方法解析target获取服务地址的信息调用ClientConn.NewAddress和NewServiceConfig这两个callback把服务信息传递给上层的调用方返回Resolver接口实例给上层上层可以通过Resolver.ResolveNow方法主动刷新服务信息了解了resolver源码的意思之后，再看一下dns_resolver.go就比较清晰了//注册一个Builder到resolver的map里面//这个方法会被默认调用，了解go的init可以自行百度func init() { resolver.Register(NewBuilder())}func NewBuilder() resolver.Builder {//创建一个resolver.Builder的实例 return &dnsBuilder{minFreq: defaultFreq}}func (b *dnsBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOption) (resolver.Resolver, error) { //解析target拿到ip和端口 host, port, err := parseTarget(target.Endpoint, defaultPort) if err != nil { return nil, err } // IP address. if net.ParseIP(host) != nil { host, _ = formatIP(host) addr := []resolver.Address{{Addr: host + “:” + port}} i := &ipResolver{ cc: cc, ip: addr, rn: make(chan struct{}, 1), q: make(chan struct{}), } cc.NewAddress(addr) go i.watcher() return i, nil } // DNS address (non-IP). ctx, cancel := context.WithCancel(context.Background()) d := &dnsResolver{ freq: b.minFreq, backoff: backoff.Exponential{MaxDelay: b.minFreq}, host: host, port: port, ctx: ctx, cancel: cancel, cc: cc, t: time.NewTimer(0), rn: make(chan struct{}, 1), disableServiceConfig: opts.DisableServiceConfig, } if target.Authority == "" { d.resolver = defaultResolver } else { d.resolver, err = customAuthorityResolver(target.Authority) if err != nil { return nil, err } } d.wg.Add(1) go d.watcher()//起一个goroutine，因为watcher这个方法是个死循环，当定时器 return d, nil}func (d *dnsResolver) watcher() { defer d.wg.Done() for { //这个select没有default，当没有case满足时会一直阻塞 //结束阻塞的条件是定时器超时d.t.C，或者d.rn这个channel中有数据可读 select { case <-d.ctx.Done(): return case <-d.t.C: case <-d.rn: } result, sc := d.lookup() // Next lookup should happen within an interval defined by d.freq. It may be // more often due to exponential retry on empty address list. if len(result) == 0 { d.retryCount++ d.t.Reset(d.backoff.Backoff(d.retryCount)) } else { d.retryCount = 0 d.t.Reset(d.freq) } //resolver.ClientConn的两个callback的调用，实现服务信息传入上层 d.cc.NewServiceConfig(sc) d.cc.NewAddress(result) }}//向channel中写入，用于结束watcher中那个select的阻塞状态，后面的代码就是重新查询服务信息的逻辑func (i *ipResolver) ResolveNow(opt resolver.ResolveNowOption) { select { case i.rn <- struct{}{}: default: }}实现consul_resovler上面我们了解了grpc的resolver的机制，接下来实现consul_resolver, 我们先把代码的架子搭起来init() //返回一个resolver.Builder的实例//实现resolver.Builder的接口中的所有方法就是一个resolver.Buildertype consulBuidler strcut {}func (cb *consulBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOption) (resolver.Resolver, error) { //TODO 解析target, 拿到consul的ip和端口 //TODO 用consul的go api连接consul，查询服务结点信息，并且调用resolver.ClientConn的两个callback}func (cb *consulBuilder) Scheme() string { return “consul”}//ResolverNow方法什么也不做，因为和consul保持了发布订阅的关系//不需要像dns_resolver那个定时的去刷新func (cr *consulResolver) ResolveNow(opt resolver.ResolveNowOption) {}//暂时先什么也不做吧func (cr *consulResolver) Close() {}现在来看，实现consul_resolver.go最大的问题就是怎么用consul提供的go api了，参考这篇文章就可以了，然后consul_resolver.go的代码就出来了package consulimport ( “errors” “fmt” “github.com/hashicorp/consul/api” “google.golang.org/grpc/resolver” “regexp” “sync”)const ( defaultPort = “8500”)var ( errMissingAddr = errors.New(“consul resolver: missing address”) errAddrMisMatch = errors.New(“consul resolver: invalied uri”) errEndsWithColon = errors.New(“consul resolver: missing port after port-separator colon”) regexConsul, _ = regexp.Compile("^([A-z0-9.]+)(:[0-9]{1,5})?/([A-z_]+)$"))func Init() { fmt.Printf(“calling consul init\n”) resolver.Register(NewBuilder())}type consulBuilder struct {}type consulResolver struct { address string wg sync.WaitGroup cc resolver.ClientConn name string disableServiceConfig bool lastIndex uint64}func NewBuilder() resolver.Builder { return &consulBuilder{}}func (cb *consulBuilder) Build(target resolver.Target, cc resolver.ClientConn, opts resolver.BuildOption) (resolver.Resolver, error) { fmt.Printf(“calling consul build\n”) fmt.Printf(“target: %v\n”, target) host, port, name, err := parseTarget(fmt.Sprintf("%s/%s", target.Authority, target.Endpoint)) if err != nil { return nil, err } cr := &consulResolver{ address: fmt.Sprintf("%s%s", host, port), name: name, cc: cc, disableServiceConfig: opts.DisableServiceConfig, lastIndex: 0, } cr.wg.Add(1) go cr.watcher() return cr, nil}func (cr *consulResolver) watcher() { fmt.Printf(“calling consul watcher\n”) config := api.DefaultConfig() config.Address = cr.address client, err := api.NewClient(config) if err != nil { fmt.Printf(“error create consul client: %v\n”, err) return } for { services, metainfo, err := client.Health().Service(cr.name, cr.name, true, &api.QueryOptions{WaitIndex: cr.lastIndex}) if err != nil { fmt.Printf(“error retrieving instances from Consul: %v”, err) } cr.lastIndex = metainfo.LastIndex var newAddrs []resolver.Address for _, service := range services { addr := fmt.Sprintf("%v:%v", service.Service.Address, service.Service.Port) newAddrs = append(newAddrs, resolver.Address{Addr: addr}) } fmt.Printf(“adding service addrs\n”) fmt.Printf(“newAddrs: %v\n”, newAddrs) cr.cc.NewAddress(newAddrs) cr.cc.NewServiceConfig(cr.name) }}func (cb *consulBuilder) Scheme() string { return “consul”}func (cr *consulResolver) ResolveNow(opt resolver.ResolveNowOption) {}func (cr *consulResolver) Close() {}func parseTarget(target string) (host, port, name string, err error) { fmt.Printf(“target uri: %v\n”, target) if target == "" { return “”, “”, “”, errMissingAddr } if !regexConsul.MatchString(target) { return “”, “”, “”, errAddrMisMatch } groups := regexConsul.FindStringSubmatch(target) host = groups[1] port = groups[2] name = groups[3] if port == "" { port = defaultPort } return host, port, name, nil}到此，grpc客户端服务发现就搞定了。consul的服务注册服务注册直接用consul的go api就可以了，也是参考前一篇文章，简单的封装一下，consul_register.go的代码如下:package consulimport ( “fmt” “github.com/hashicorp/consul/api” “time”)type ConsulService struct { IP string Port int Tag []string Name string}func RegitserService(ca string, cs *ConsulService) { //register consul consulConfig := api.DefaultConfig() consulConfig.Address = ca client, err := api.NewClient(consulConfig) if err != nil { fmt.Printf(“NewClient error\n%v”, err) return } agent := client.Agent() interval := time.Duration(10) * time.Second deregister := time.Duration(1) * time.Minute reg := &api.AgentServiceRegistration{ ID: fmt.Sprintf("%v-%v-%v", cs.Name, cs.IP, cs.Port), // 服务节点的名称 Name: cs.Name, // 服务名称 Tags: cs.Tag, // tag，可以为空 Port: cs.Port, // 服务端口 Address: cs.IP, // 服务 IP Check: &api.AgentServiceCheck{ // 健康检查 Interval: interval.String(), // 健康检查间隔 GRPC: fmt.Sprintf("%v:%v/%v", cs.IP, cs.Port, cs.Name), // grpc 支持，执行健康检查的地址，service 会传到 Health.Check 函数中 DeregisterCriticalServiceAfter: deregister.String(), // 注销时间，相当于过期时间 }, } fmt.Printf(“registing to %v\n”, ca) if err := agent.ServiceRegister(reg); err != nil { fmt.Printf(“Service Register error\n%v”, err) return }}改造一下grpc的helloworld把grpc的helloworld的demo改一下，用consul来做服务注册和发现。server端代码:package mainimport ( “context” “fmt” “google.golang.org/grpc” “google.golang.org/grpc/health/grpc_health_v1” “log” “net” “server/internal/consul” pb “server/proto/helloworld”)const ( port = “:50051”)// server is used to implement helloworld.GreeterServer.type server struct{}// SayHello implements helloworld.GreeterServerfunc (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloReply, error) { log.Printf(“Received: %v”, in.Name) return &pb.HelloReply{Message: “Hello " + in.Name}, nil}func RegisterToConsul() { consul.RegitserService(“127.0.0.1:8500”, &consul.ConsulService{ Name: “helloworld”, Tag: []string{“helloworld”}, IP: “127.0.0.1”, Port: 50051, })}//healthtype HealthImpl struct{}// Check 实现健康检查接口，这里直接返回健康状态，这里也可以有更复杂的健康检查策略，比如根据服务器负载来返回func (h *HealthImpl) Check(ctx context.Context, req *grpc_health_v1.HealthCheckRequest) (*grpc_health_v1.HealthCheckResponse, error) { fmt.Print(“health checking\n”) return &grpc_health_v1.HealthCheckResponse{ Status: grpc_health_v1.HealthCheckResponse_SERVING, }, nil}func (h *HealthImpl) Watch(req grpc_health_v1.HealthCheckRequest, w grpc_health_v1.Health_WatchServer) error { return nil}func main() { lis, err := net.Listen(“tcp”, port) if err != nil { log.Fatalf(“failed to listen: %v”, err) } s := grpc.NewServer() pb.RegisterGreeterServer(s, &server{}) grpc_health_v1.RegisterHealthServer(s, &HealthImpl{}) RegisterToConsul() if err := s.Serve(lis); err != nil { log.Fatalf(“failed to serve: %v”, err) }}client端代码:package mainimport ( “client/internal/consul” pb “client/proto/helloworld” “context” “google.golang.org/grpc” “log” “os” “time”)const ( target = “consul://127.0.0.1:8500/helloworld” defaultName = “world”)func main() { consul.Init() // Set up a connection to the server. ctx, _ := context.WithTimeout(context.Background(), 5time.Second) conn, err := grpc.DialContext(ctx, target, grpc.WithBlock(), grpc.WithInsecure(), grpc.WithBalancerName(“round_robin”)) if err != nil { log.Fatalf(“did not connect: %v”, err) } defer conn.Close() c := pb.NewGreeterClient(conn) // Contact the server and print out its response. name := defaultName if len(os.Args) > 1 { name = os.Args[1] } for { ctx, _ := context.WithTimeout(context.Background(), time.Second) r, err := c.SayHello(ctx, &pb.HelloRequest{Name: name}) if err != nil { log.Fatalf(“could not greet: %v”, err) } log.Printf(“Greeting: %s”, r.Message) time.Sleep(time.Second * 2) }}运行一把启动consulconsul agent -dev启动hello servercd servergo run cmd/main.go启动hello clientcd clientgo run cmd/main.go运行结果：//client2019/03/07 17:22:04 Greeting: Hello world2019/03/07 17:22:06 Greeting: Hello world//server2019/03/07 17:22:04 Received: world2019/03/07 17:22:06 Received: world完整工程的git地址工程使用方法：cd servergo mod tidygo run cmd/main.gocd clientgo mod tidygo run cmd/main.go请自行解决防火墙的问题参考文章grpc 名称发现与负载均衡golang consul-grpc 服务注册与发现gRPC Client-Side Load Balancing in Gogodoc grpcconsul go api
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