# go微服务框架kratos学习笔记六(kratos 服务发现 discovery)

go微服务框架kratos学习笔记六(kratos 服务发现 discovery)

目录

• go微服务框架kratos学习笔记六(kratos 服务发现 discovery)
  • http api
    • register 服务注册
    • fetch 获取实例
    • fetchs 批量获取实例
    • polls 批量获取实例
    • nodes 批量获取节点
    • renew 心跳
    • cancel 下线
  • 应用发现逻辑
  • 服务注册
    • 服务注册demo
    • 服务注册逻辑
  • 服务发现
    • 测试调用
  • 简单看看官方grpc服务发现逻辑
    • context deadline exceeded
    • 简单看看官方grpc服务发现逻辑

---

除了上次的warden直连方式外，kratos有另一个服务发现sdk : discovery

discovery 可以先简单理解为一个http服务、

它最简单的发现过程可能是这样的:

1、service 向discovery 服务注册 appid

2、client 通过 appid 从discovery 查询 service 的addr

当然 远不止这么简单，还包含了很多功能在里面的，例如服务自发现、负载均衡等

本节仅先看个最简单的服务发现的demo

首先走一遍discovery的http的api

http api

// innerRouter init local router api path.
func innerRouter(e *bm.Engine) {
	group := e.Group("/discovery")
	{
		group.POST("/register", register)
		group.POST("/renew", renew)
		group.POST("/cancel", cancel)
		group.GET("/fetch/all", initProtect, fetchAll)
		group.GET("/fetch", initProtect, fetch)
		group.GET("/fetchs", initProtect, fetchs)
		group.GET("/poll", initProtect, poll)
		group.GET("/polls", initProtect, polls)
		//manager
		group.POST("/set", set)
		group.GET("/nodes", initProtect, nodes)
	}
}

discovery里面的bm引擎注册了这些接口, 接着我用postman 测了测。

register 服务注册

fetch 获取实例

fetchs 批量获取实例

polls 批量获取实例

nodes 批量获取节点

renew 心跳

POST http://HOST/discovery/renew

curl 'http://127.0.0.1:7171/discovery/renew' -d "zone=sh1&env=test&appid=provider&hostname=myhostname"

*****成功*****
{
    "code":0,
    "message":""
}
****失败****
{
    "code":-400,
    "message":"-400"
}

cancel 下线

POST http://HOST/discovery/cancel

curl 'http://127.0.0.1:7171/discovery/cancel' -d "zone=sh1&env=test&appid=provider&hostname=myhostname"

*****成功*****
{
    "code":0,
    "message":""
}
****失败****
{
    "code":-400,
    "message":"-400"
}

应用发现逻辑

官方应用发现实现逻辑

选择可用的节点，将应用appid加入poll的appid列表

如果polls请求返回err，则切换node节点，切换逻辑与自发现错误时切换逻辑一致

如果polls返回-304 ，说明appid无变更，重新发起poll监听变更

polls接口返回appid的instances列表，完成服务发现，根据需要选择不同的负载均衡算法进行节点的调度

服务注册

服务注册demo

直接new一个demo服务然后将demo服务注册到discovery

主函数里面服务注册部分添加类似下面注册代码。

	ip := "127.0.0.1"
	port := "9000"
	hn, _ := os.Hostname()
	dis := discovery.New(nil)
	ins := &naming.Instance{
		Zone:     env.Zone,
		Env:      env.DeployEnv,
		AppID:    "demo.service",
		Hostname: hn,
		Addrs: []string{
			"grpc://" + ip + ":" + port,
		},
	}

	cancel, err := dis.Register(context.Background(), ins)
	if err != nil {
		panic(err)
	}

	defer cancel()

panic 找不到节点,这个是我们discovery的节点地址 可以在环境变量里面添加。

I:\VSProject\kratos-note\kratos-note\warden\discovery\server>kratos run
INFO 01/04-19:32:28.198 I:/VSProject/go/pkg/mod/github.com/bilibili/kratos@v0.3.2-0.20191224125553-6e1180f53a8e/pkg/net/rpc/warden/server.go:329 warden: start grpc listen addr: [::]:9000
panic: invalid discovery config nodes:[] region:region01 zone:zone01 deployEnv:dev host:DESKTOP-NUEKD5O

配置discovery节点后成功注册

I:\VSProject\kratos-note\kratos-note\warden\discovery\server>set DISCOVERY_NODES=127.0.0.1:7171

I:\VSProject\kratos-note\kratos-note\warden\discovery\server>kratos run
INFO 01/04-19:40:25.426 I:/VSProject/kratos-note/kratos-note/warden/discovery/server/cmd/main.go:23 abc start
2020/01/04 19:40:25 start watch filepath: I:\VSProject\kratos-note\kratos-note\warden\discovery\server\configs
INFO 01/04-19:40:25.497 I:/VSProject/go/pkg/mod/github.com/bilibili/kratos@v0.3.2-0.20191224125553-6e1180f53a8e/pkg/net/http/blademaster/server.go:98 blademaster: start http listen addr: 0.0.0.0:8000
[warden] config is Deprecated, argument will be ignored. please use -grpc flag or GRPC env to configure warden server.
INFO 01/04-19:40:25.500 I:/VSProject/go/pkg/mod/github.com/bilibili/kratos@v0.3.2-0.20191224125553-6e1180f53a8e/pkg/net/rpc/warden/server.go:329 warden: start grpc listen addr: [::]:9000
INFO 01/04-19:40:25.501 I:/VSProject/go/pkg/mod/github.com/bilibili/kratos@v0.3.2-0.20191224125553-6e1180f53a8e/pkg/naming/discovery/discovery.go:248 disocvery: AddWatch(infra.discovery) already watch(false)
INFO 01/04-19:40:25.514 I:/VSProject/go/pkg/mod/github.com/bilibili/kratos@v0.3.2-0.20191224125553-6e1180f53a8e/pkg/naming/discovery/discovery.go:631 discovery: successfully polls(http://127.0.0.1:7171/discovery/polls?appid=infra.discovery&env=dev&hostname=DESKTOP-NUEKD5O&latest_timestamp=0) instances ({"infra.discovery":{"instances":{"sh001":[{"region":"sh","zone":"sh001","env":"dev","appid":"infra.discovery","hostname":"test1","addrs":["http://127.0.0.1:7171"],"version":"","latest_timestamp":1578122538945305700,"metadata":null,"status":1}]},"latest_timestamp":1578122538945305700,"scheduler":null}})
INFO 01/04-19:40:25.527 I:/VSProject/go/pkg/mod/github.com/bilibili/kratos@v0.3.2-0.20191224125553-6e1180f53a8e/pkg/naming/discovery/discovery.go:414 discovery: register client.Get(http://127.0.0.1:7171/discovery/register) env(dev) appid(demo.service) addrs([grpc://127.0.0.1:9000]) success

服务注册逻辑

现在我们跟着日志走一遍。

如图理解，服务注册逻辑应该是register -> renew ->cancel 注册 然后 不停给心跳 最后取消注册。

截取一条本地服务注册日志

操作大概是：

1、启动discovery服务

2、启动demo.server 注册demo.server appid 服务

3、过一小会等待心跳，关闭demo.server

接着可以看到整个日志的过程大致上是 ：

1、 0 : 启动dicovery服务

2、 2/3/4 : 服务初始化

3、 5 : polls 长轮循 infra.discovery 服务自发现

4、 6/7: 新的连接 & 服务注册、这时候我们起动的demo.server服务注册上来了

5、 9 : polls 长轮循 infra.discovery 服务自发现

6、 10 : renew心跳

7、 12 : 最后我杀掉了注册的服务，出现了cancel请求。

从日志看逻辑理解基本上也没有太多偏差，接着看看服务发现。

0：discovery -conf discovery-example.toml -log.v=0
1：
2：INFO 01/10-10:31:19.575 C:/server/src/go/src/discovery/discovery/syncup.go:160 discovery 3：changed nodes:[127.0.0.1:7171] zones:map[]
4：INFO 01/10-10:31:19.575 C:/server/src/go/pkg/mod/github.com/bilibili/kratos@v0.1.0/pkg/net/http/blademaster/server.go:98 blademaster: start http listen addr: 127.0.0.1:7171
INFO 01/10-10:31:19.575 C:/server/src/go/src/discovery/registry/registry.go:219 Polls from(test1) new connection(1)

5:INFO 01/10-10:31:31.796 http-access-log ts=0 method=GET ip=127.0.0.1 traceid= user=no_user params=appid=infra.discovery&env=dev&hostname=DESKTOP-9NFHKD0&latest_timestamp=0 msg=0 stack=<nil> err= timeout_quota=39.98 path=/discovery/polls ret=0

6:INFO 01/10-10:31:31.798 C:/server/src/go/src/discovery/registry/registry.go:219 Polls from(DESKTOP-9NFHKD0) new connection(1)

7:INFO 01/10-10:31:31.799 http-access-log method=POST user=no_user path=/discovery/register err= ts=0 params=addrs=grpc%3A%2F%2F127.0.0.1%3A9000&appid=demo.service&env=dev&hostname=DESKTOP-9NFHKD0&metadata=&region=region01&status=1&version=&zone=zone01 stack=<nil> ret=0 timeout_quota=39.98 ip=127.0.0.1 msg=0 traceid=

8:INFO 01/10-10:32:01.799 C:/server/src/go/src/discovery/registry/registry.go:370 DelConns from(DESKTOP-9NFHKD0) delete(1)

9:ERROR 01/10-10:32:01.799 http-access-log method=GET ip=127.0.0.1 err=-304 timeout_quota=39.98 user=no_user path=/discovery/polls params=appid=infra.discovery&env=dev&hostname=DESKTOP-9NFHKD0&latest_timestamp=1578623479566211700 ret=-304 msg=-304 stack=-304 ts=30.0011342 traceid=

10:INFO 01/10-10:32:01.799 http-access-log msg=0 err= timeout_quota=39.98 method=POST ip=127.0.0.1 user=no_user ret=0 path=/discovery/renew traceid= params=appid=demo.service&env=dev&hostname=DESKTOP-9NFHKD0&region=region01&zone=zone01 stack=<nil> ts=0

11:INFO 01/10-10:32:01.800 C:/server/src/go/src/discovery/registry/registry.go:219 Polls from(DESKTOP-9NFHKD0) new connection(1)

12:INFO 01/10-10:32:08.499 http-access-log timeout_quota=39.98 path=/discovery/cancel ret=0 stack=<nil> ip=127.0.0.1 msg=0 traceid= ts=0 method=POST user=no_user err= params=appid=demo.service&env=dev&hostname=DESKTOP-9NFHKD0&region=region01&zone=zone01

服务发现

同样先配置discovert节点 set DISCOVERY_NODES=127.0.0.1:7171

NewClient()改成如下方式

package dao

import (
	"context"

	"github.com/bilibili/kratos/pkg/naming/discovery"
	"github.com/bilibili/kratos/pkg/net/rpc/warden"
	"github.com/bilibili/kratos/pkg/net/rpc/warden/resolver"

	"google.golang.org/grpc"
)

// AppID your appid, ensure unique.
const AppID = "demo.service" // NOTE: example

func init(){
	// NOTE: 注意这段代码，表示要使用discovery进行服务发现
	// NOTE: 还需注意的是，resolver.Register是全局生效的，所以建议该代码放在进程初始化的时候执行
	// NOTE: ！！！切记不要在一个进程内进行多个不同中间件的Register！！！
	// NOTE: 在启动应用时，可以通过flag(-discovery.nodes) 或者 环境配置(DISCOVERY_NODES)指定discovery节点
	resolver.Register(discovery.Builder())
}

// NewClient new member grpc client
func NewClient(cfg *warden.ClientConfig, opts ...grpc.DialOption) (DemoClient, error) {
	client := warden.NewClient(cfg, opts...)
	conn, err := client.Dial(context.Background(), "discovery://default/"+AppID)
	if err != nil {
		return nil, err
	}
	// 注意替换这里：
	// NewDemoClient方法是在"api"目录下代码生成的
	// 对应proto文件内自定义的service名字，请使用正确方法名替换
	return NewDemoClient(conn), nil
}

同时嵌入dao结构里面、和上次warden direct方式一样做SayHello接口测试调用。

// dao dao.
type dao struct {
	db          *sql.DB
	redis       *redis.Redis
	mc          *memcache.Memcache
	demoClient  demoapi.DemoClient
	cache *fanout.Fanout
	demoExpire int32
}

// New new a dao and return.
func New(r *redis.Redis, mc *memcache.Memcache, db *sql.DB) (d Dao, err error) {
	var cfg struct{
		DemoExpire xtime.Duration
	}
	if err = paladin.Get("application.toml").UnmarshalTOML(&cfg); err != nil {
		return
	}

	grpccfg := &warden.ClientConfig{
		Dial:              xtime.Duration(time.Second * 10),
		Timeout:           xtime.Duration(time.Millisecond * 250),
		Subset:            50,
		KeepAliveInterval: xtime.Duration(time.Second * 60),
		KeepAliveTimeout:  xtime.Duration(time.Second * 20),
	}
	//paladin.Get("grpc.toml").UnmarshalTOML(grpccfg)
	var grpcClient demoapi.DemoClient
	grpcClient, err = NewClient(grpccfg)

	d = &dao{
		db: db,
		redis: r,
		mc: mc,
		demoClient : grpcClient,
		cache: fanout.New("cache"),
		demoExpire: int32(time.Duration(cfg.DemoExpire) / time.Second),
	}
	return
}

测试调用

操作流程

1、启动discovery服务

2、启动demo.server 注册为 demo.server 服务

3、启动demo.client、

4、最后从demo.client的SayHello http接口 调到demo.server的grpc SayHello 接口。

简单看看官方grpc服务发现逻辑

context deadline exceeded

我发现个别时候调用做服务发现，会发现client起不来， context deadline exceeded。

因为我把new client加在了dao里面，超时的话，demo.client就直接pannic了

根据client日志可以发现

warden client: dial discovery://default/demo.service?subset=50 error context deadline exceeded!panic: context deadline exceeded

client : host:127.0.0.1:7171, url:http://127.0.0.1:7171/discovery/polls?appid=infra.discovery&env=dev&hostname=DESKTOP-9NFHKD0&latest_timestamp=1578902420717217500

在调用discovery polls的时候超时了，我配置的grpc dial 期限为10s， 在官方discovery文档介绍中写到discovery在做服务节点自发现的时候，如果server节点实例没有变更，则接口会阻塞直到30s返回-304。(poll(polls) 接口为长轮训接口)

关于服务自发现的话，这里不细看了，本节只关注应用发现逻辑，感兴趣可以去discovery上看看。

INFO 01/10-15:22:34.436 http-access-log method=GET path=/discovery/polls user=no_user params=appid=infra.discovery&env=dev&hostname=CLII&latest_timestamp=0 stack=<nil> err= timeout_quota=39.98 ts=0 msg=0 traceid= ip=127.0.0.1 ret=0
INFO 01/10-15:22:34.438 C:/server/src/go/src/discovery/registry/registry.go:222 Polls from(CLII) new connection(1)
INFO 01/10-15:22:34.440 C:/server/src/go/src/discovery/registry/registry.go:228 Polls from(CLII) reuse connection(2)
INFO 01/10-15:22:44.219 C:/server/src/go/src/discovery/registry/registry.go:373 DelConns from(DESKTOP-9NFHKD0) delete(1)
ERROR 01/10-15:22:44.219 http-access-log path=/discovery/polls ret=-304 msg=-304 timeout_quota=39.98 ip=127.0.0.1 params=appid=infra.discovery&env=dev&hostname=DESKTOP-9NFHKD0&latest_timestamp=1578637331623587200 user=no_user ts=39.9808023 err=-304 traceid= method=GET stack=-304
INFO 01/10-15:22:44.221 C:/server/src/go/src/discovery/registry/registry.go:222 Polls from(DESKTOP-9NFHKD0) new connection(1)
INFO 01/10-15:22:44.525 http-access-log ts=0 method=POST ip=127.0.0.1 user=no_user stack=<nil> path=/discovery/renew err= traceid= ret=0 msg=0 timeout_quota=39.98 params=appid=demo.service&env=dev&hostname=DESKTOP-9NFHKD0&region=region01&zone=zone01
INFO 01/10-15:23:04.438 C:/server/src/go/src/discovery/registry/registry.go:370 DelConns from(CLII) count decr(2)
ERROR 01/10-15:23:04.438 http-access-log msg=-304 ts=30.0002154 method=GET err=-304 stack=-304 timeout_quota=39.98 ip=127.0.0.1 user=no_user path=/discovery/polls params=appid=infra.discovery&env=dev&hostname=CLII&latest_timestamp=1578637331623587200 ret=-304 traceid=
INFO 01/10-15:23:04.440 C:/server/src/go/src/discovery/registry/registry.go:373 DelConns from(CLII) delete(1)
ERROR 01/10-15:23:04.440 http-access-log ts=30.0013758 traceid= user=no_user path=/discovery/polls ret=-304 err=-304 method=GET ip=127.0.0.1 params=appid=infra.discovery&appid=demo.service&env=dev&hostname=CLII&latest_timestamp=1578637331623587200&latest_timestamp=0 msg=-304 stack=-304 timeout_quota=39.98

结合discovery 日志

15:22:34的client发dial

15:22:45左右client panic

15:23:04dicovery才回复一个-304 (实例信息无变更)

---

这实际上是因为 client.Dial() 里面封装了grpc官方的服务发现，当然最终走的是kratos warden里面的实现的grpc官方服务发现逻辑。

下面简单看看这层逻辑，很绕，我也没看懂，只能简单看看，有机会接触再补个详细的。

简单看看官方grpc服务发现逻辑

// NewClient new grpc client
func NewClient(cfg *warden.ClientConfig, opts ...grpc.DialOption) (demoapi.DemoClient, error) {
	client := warden.NewClient(cfg, opts...)
	cc, err := client.Dial(context.Background(), fmt.Sprintf("discovery://default/%s", AppID))
	if err != nil {
		return nil, err
	}
	return demoapi.NewDemoClient(cc), nil
}

实际上 client.Dial() 里面会有会有这么一个流程 :

client.Dial() - > grpc里面DialContext() -> parser target 的 scheme 然后获取 (这里是discovery) 对应的Builder

	if cc.dopts.resolverBuilder == nil {
		// Only try to parse target when resolver builder is not already set.
		cc.parsedTarget = parseTarget(cc.target)
		grpclog.Infof("parsed scheme: %q", cc.parsedTarget.Scheme)
		cc.dopts.resolverBuilder = resolver.Get(cc.parsedTarget.Scheme)
		if cc.dopts.resolverBuilder == nil {
			// If resolver builder is still nil, the parsed target's scheme is
			// not registered. Fallback to default resolver and set Endpoint to
			// the original target.
			grpclog.Infof("scheme %q not registered, fallback to default scheme", cc.parsedTarget.Scheme)
			cc.parsedTarget = resolver.Target{
				Scheme:   resolver.GetDefaultScheme(),
				Endpoint: target,
			}
			cc.dopts.resolverBuilder = resolver.Get(cc.parsedTarget.Scheme)
		}
	} else {
		cc.parsedTarget = resolver.Target{Endpoint: target}
	}

---

DialContext() 成功会得到 -> 结构体ClientConn -> ClientConn.resolverWrapper 初始化 -> 调用build()

	defer ccr.resolverMu.Unlock()

	ccr.resolver, err = rb.Build(cc.parsedTarget, ccr, rbo)

// ClientConn represents a virtual connection to a conceptual endpoint, to
// perform RPCs.
//
// A ClientConn is free to have zero or more actual connections to the endpoint
// based on configuration, load, etc. It is also free to determine which actual
// endpoints to use and may change it every RPC, permitting client-side load
// balancing.
//
// A ClientConn encapsulates a range of functionality including name
// resolution, TCP connection establishment (with retries and backoff) and TLS
// handshakes. It also handles errors on established connections by
// re-resolving the name and reconnecting.
type ClientConn struct {
	ctx    context.Context
	cancel context.CancelFunc

	target       string
	parsedTarget resolver.Target
	authority    string
	dopts        dialOptions
	csMgr        *connectivityStateManager

	balancerBuildOpts balancer.BuildOptions
	blockingpicker    *pickerWrapper

	mu              sync.RWMutex
	resolverWrapper *ccResolverWrapper
	sc              *ServiceConfig
	conns           map[*addrConn]struct{}
	// Keepalive parameter can be updated if a GoAway is received.
	mkp             keepalive.ClientParameters
	curBalancerName string
	balancerWrapper *ccBalancerWrapper
	retryThrottler  atomic.Value

	firstResolveEvent *grpcsync.Event

	channelzID int64 // channelz unique identification number
	czData     *channelzData
}

---

用户Builder的实现进行UpdateState —> ClientConn的updateResolverState -> updateResolverState -> Address初始化等grpc官方逻辑

// Builder creates a resolver that will be used to watch name resolution updates.
type Builder interface {
	// Build creates a new resolver for the given target.
	//
	// gRPC dial calls Build synchronously, and fails if the returned error is
	// not nil.
	Build(target Target, cc ClientConn, opts BuildOptions) (Resolver, error)
	// Scheme returns the scheme supported by this resolver.
	// Scheme is defined at https://github.com/grpc/grpc/blob/master/doc/naming.md.
	Scheme() string
}

// ClientConn contains the callbacks for resolver to notify any updates
// to the gRPC ClientConn.
//
// This interface is to be implemented by gRPC. Users should not need a
// brand new implementation of this interface. For the situations like
// testing, the new implementation should embed this interface. This allows
// gRPC to add new methods to this interface.
type ClientConn interface {
	// UpdateState updates the state of the ClientConn appropriately.
	UpdateState(State)
	// ReportError notifies the ClientConn that the Resolver encountered an
	// error.  The ClientConn will notify the load balancer and begin calling
	// ResolveNow on the Resolver with exponential backoff.
	ReportError(error)
	// NewAddress is called by resolver to notify ClientConn a new list
	// of resolved addresses.
	// The address list should be the complete list of resolved addresses.
	//
	// Deprecated: Use UpdateState instead.
	NewAddress(addresses []Address)
	// NewServiceConfig is called by resolver to notify ClientConn a new
	// service config. The service config should be provided as a json string.
	//
	// Deprecated: Use UpdateState instead.
	NewServiceConfig(serviceConfig string)
	// ParseServiceConfig parses the provided service config and returns an
	// object that provides the parsed config.
	ParseServiceConfig(serviceConfigJSON string) *serviceconfig.ParseResult
}

kratos discovery

warden包装了gRPC的整个服务发现实现逻辑，代码分别位于pkg/naming/naming.go和warden/resolver/resolver.go中

naming.go定义了用于描述业务实例的Instance结构、用于服务注册的Registry接口、用于服务发现的Resolver接口。

// Resolver resolve naming service
type Resolver interface {
	Fetch(context.Context) (*InstancesInfo, bool)
	Watch() <-chan struct{}
	Close() error
}

// Registry Register an instance and renew automatically.
type Registry interface {
	Register(ctx context.Context, ins *Instance) (cancel context.CancelFunc, err error)
	Close() error
}

// InstancesInfo instance info.
type InstancesInfo struct {
	Instances map[string][]*Instance `json:"instances"`
	LastTs    int64                  `json:"latest_timestamp"`
	Scheduler *Scheduler             `json:"scheduler"`
}

resolver.go内实现了gRPC官方的resolver.Builder和resolver.Resolver接口，同时也暴露了naming.go内的naming.Builder和naming.Resolver接口

// Resolver resolve naming service
type Resolver interface {
	Fetch(context.Context) (*InstancesInfo, bool)
	Watch() <-chan struct{}
	Close() error
}

// Builder resolver builder.
type Builder interface {
	Build(id string) Resolver
	Scheme() string
}

kratos对grpc的Build做了包装，只需要传对应的服务的appid即可：warden/resolver/resolver.go在gRPC进行调用后，会根据Scheme方法查询对应的naming.Builder实现并调用Build将id传入。而实现naming.Resolver即可通过appid去对应的服务发现中间件(这里是discovery服务)进行实例信息的查询(Fetch接口)、除了简单进行Fetch操作外还多了Watch方法，用于监听服务发现中间件的节点变化情况，能够实时的进行服务实例信息的更新。

在naming/discovery内实现了基于discovery为中间件的服务注册与发现逻辑。大致上也可以在这里面看到做了对discovery服务中间件的polls请求。

// Build disovery resovler builder.
func (d *Discovery) Build(appid string, opts ...naming.BuildOpt) naming.Resolver {
	r := &Resolve{
		id:    appid,
		d:     d,
		event: make(chan struct{}, 1),
		opt:   new(naming.BuildOptions),
	}
	for _, opt := range opts {
		opt.Apply(r.opt)
	}
	d.mutex.Lock()
	app, ok := d.apps[appid]
	if !ok {
		app = &appInfo{
			resolver: make(map[*Resolve]struct{}),
		}
		d.apps[appid] = app
		cancel := d.cancelPolls
		if cancel != nil {
			cancel()
		}
	}
	app.resolver[r] = struct{}{}
	d.mutex.Unlock()
	if ok {
		select {
		case r.event <- struct{}{}:
		default:
		}
	}
	log.Info("disocvery: AddWatch(%s) already watch(%v)", appid, ok)
	d.once.Do(func() {
		go d.serverproc()
	})
	return r
}

func (d *Discovery) serverproc() {
	var (
		retry  int
		ctx    context.Context
		cancel context.CancelFunc
	)
	ticker := time.NewTicker(time.Minute * 30)
	defer ticker.Stop()
	for {
		if ctx == nil {
			ctx, cancel = context.WithCancel(d.ctx)
			d.mutex.Lock()
			d.cancelPolls = cancel
			d.mutex.Unlock()
		}
		select {
		case <-d.ctx.Done():
			return
		case <-ticker.C:
			d.switchNode()
		default:
		}
		apps, err := d.polls(ctx)
		if err != nil {
			d.switchNode()
			if ctx.Err() == context.Canceled {
				ctx = nil
				continue
			}
			time.Sleep(time.Second)
			retry++
			continue
		}
		retry = 0
		d.broadcast(apps)
	}
}