go微服務框架kratos學習筆記六(kratos 服務發現 discovery)

go微服務框架kratos學習筆記六(kratos 服務發現 discovery)
- http api
  - register 服務注冊
  - fetch 獲取實體
  - fetchs 批量獲取實體
  - polls 批量獲取實體
  - nodes 批量獲取節點
  - renew 心跳
  - cancel 下線
- 應用發現邏輯
- 服務注冊
  - 服務注冊demo
  - 服務注冊邏輯
- 服務發現
  - 測驗呼叫
- 簡單看看官方grpc服務發現邏輯
  - context deadline exceeded
  - 簡單看看官方grpc服務發現邏輯

除了上次的warden直連方式外，kratos有另一個服務發現sdk : discovery

discovery 可以先簡單理解為一個http服務、

它最簡單的發現程序可能是這樣的:

1、service 向discovery 服務注冊 appid
2、client 通過 appid 從discovery 查詢 service 的addr

當然遠不止這么簡單，還包含了很多功能在里面的，例如服務自發現、負載均衡等

本節僅先看個最簡單的服務發現的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引擎注冊了這些介面, 接著我用postman 測了測，

register 服務注冊

fetch 獲取實體

fetchs 批量獲取實體

polls 批量獲取實體

nodes 批量獲取節點

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":""
}
****失敗****
{
    "code":-400,
    "message":"-400"
}

cancel 下線

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":""
}
****失敗****
{
    "code":-400,
    "message":"-400"
}

應用發現邏輯

官方應用發現實作邏輯

選擇可用的節點，將應用appid加入poll的appid串列
如果polls請求回傳err，則切換node節點，切換邏輯與自發現錯誤時切換邏輯一致
如果polls回傳-304 ，說明appid無變更，重新發起poll監聽變更
polls介面回傳appid的instances串列，完成服務發現，根據需要選擇不同的負載均衡演算法進行節點的調度

服務注冊

服務注冊demo

直接new一個demo服務然后將demo服務注冊到discovery

主函式里面服務注冊部分添加類似下面注冊代碼，

	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 找不到節點,這個是我們discovery的節點地址可以在環境變數里面添加，

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/[email protected]/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節點后成功注冊

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/[email protected]/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/[email protected]/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/[email protected]/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/[email protected]/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/[email protected]/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

服務注冊邏輯

現在我們跟著日志走一遍，

如圖理解，服務注冊邏輯應該是register -> renew ->cancel 注冊然后不停給心跳最后取消注冊，

截取一條本地服務注冊日志

操作大概是：

1、啟動discovery服務
2、啟動demo.server 注冊demo.server appid 服務
3、過一小會等待心跳，關閉demo.server

接著可以看到整個日志的程序大致上是：

1、 0 : 啟動dicovery服務
2、 2/3/4 : 服務初始化
3、 5 : polls 長輪循 infra.discovery 服務自發現
4、 6/7: 新的連接 & 服務注冊、這時候我們起動的demo.server服務注冊上來了
5、 9 : polls 長輪循 infra.discovery 服務自發現
6、 10 : renew心跳
7、 12 : 最后我殺掉了注冊的服務，出現了cancel請求，

從日志看邏輯理解基本上也沒有太多偏差，接著看看服務發現，

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/[email protected]/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=https://www.cnblogs.com/ailumiyana/p/®ion=region01&status=1&version=&zone=zone01 stack= 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®ion=region01&zone=zone01 stack= 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= 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®ion=region01&zone=zone01

服務發現

同樣先配置discovert節點 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: 注意這段代碼，表示要使用discovery進行服務發現
	// NOTE: 還需注意的是，resolver.Register是全域生效的，所以建議該代碼放在行程初始化的時候執行
	// NOTE: ！！！切記不要在一個行程內進行多個不同中間件的Register！！！
	// NOTE: 在啟動應用時，可以通過flag(-discovery.nodes) 或者 環境配置(DISCOVERY_NODES)指定discovery節點
	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
	}
	// 注意替換這里：
	// NewDemoClient方法是在"api"目錄下代碼生成的
	// 對應proto檔案內自定義的service名字，請使用正確方法名替換
	return NewDemoClient(conn), nil
}

同時嵌入dao結構里面、和上次warden direct方式一樣做SayHello介面測驗呼叫，

// 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
}

測驗呼叫

操作流程

1、啟動discovery服務
2、啟動demo.server 注冊為 demo.server 服務
3、啟動demo.client、
4、最后從demo.client的SayHello http介面調到demo.server的grpc SayHello 介面，

簡單看看官方grpc服務發現邏輯

context deadline exceeded

我發現個別時候呼叫做服務發現，會發現client起不來， context deadline exceeded，

因為我把new client加在了dao里面，超時的話，demo.client就直接pannic了

根據client日志可以發現
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
在呼叫discovery polls的時候超時了，我配置的grpc dial 期限為10s，在官方discovery檔案介紹中寫到discovery在做服務節點自發現的時候，如果server節點實體沒有變更，則介面會阻塞直到30s回傳-304，(poll(polls) 介面為長輪訓介面)

關于服務自發現的話，這里不細看了，本節只關注應用發現邏輯，感興趣可以去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

結合discovery 日志
15:22:34的client發dial
15:22:45左右client panic
15:23:04dicovery才回復一個-304 (實體資訊無變更)

這實際上是因為 client.Dial() 里面封裝了grpc官方的服務發現，當然最終走的是kratos warden里面的實作的grpc官方服務發現邏輯，

下面簡單看看這層邏輯，很繞，我也沒看懂，只能簡單看看，有機會接觸再補個詳細的，

簡單看看官方grpc服務發現邏輯

// 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
}

實際上 client.Dial() 里面會有會有這么一個流程 :

client.Dial() - > grpc里面DialContext() -> parser target 的 scheme 然后獲取 (這里是discovery) 對應的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() 成功會得到 -> 結構體ClientConn -> ClientConn.resolverWrapper 初始化 -> 呼叫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
}

用戶Builder的實作進行UpdateState —> ClientConn的updateResolverState -> updateResolverState -> Address初始化等grpc官方邏輯

// 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包裝了gRPC的整個服務發現實作邏輯，代碼分別位于pkg/naming/naming.go和warden/resolver/resolver.go中

naming.go定義了用于描述業務實體的Instance結構、用于服務注冊的Registry介面、用于服務發現的Resolver介面，

// 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內實作了gRPC官方的resolver.Builder和resolver.Resolver介面，同時也暴露了naming.go內的naming.Builder和naming.Resolver介面

// 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對grpc的Build做了包裝，只需要傳對應的服務的appid即可：warden/resolver/resolver.go在gRPC進行呼叫后，會根據Scheme方法查詢對應的naming.Builder實作并呼叫Build將id傳入，而實作naming.Resolver即可通過appid去對應的服務發現中間件(這里是discovery服務)進行實體資訊的查詢(Fetch介面)、除了簡單進行Fetch操作外還多了Watch方法，用于監聽服務發現中間件的節點變化情況，能夠實時的進行服務實體資訊的更新，

在naming/discovery內實作了基于discovery為中間件的服務注冊與發現邏輯，大致上也可以在這里面看到做了對discovery服務中間件的polls請求，

// 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)
	}
}

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