Informer 简介

Informer 是 Client-go 中的一个核心工具包。如果 Kubernetes 的某个组件，需要 List/Get Kubernetes 中的 Object（包括pod，service等等），可以直接使用 Informer 实例中的 Lister()方法（包含 Get 和 List 方法）。Informer 最基本的功能就是 List/Get Kubernetes 中的 Object，还可以监听事件并触发回调函数等

Informer 的 Lister() 方法（List/Get），Informer 不会去请求 Kubernetes API，而是查找缓存在本地内存中的数据(由 Informer 自己维护)。好处是Informer 可以快速地返回结果，也减少对 Kubernetes API 的直接调用引起的额外开销。
Informer 只会调用 Kubernetes List 和 Watch 的 API。Informer 在初始化的时，先调用 Kubernetes List API 获得资源的全部，缓存在内存中，然后调用 Watch API 去 watch 这种 resource，维护这份缓存保持一致性
Informer 可以自定义回调函数，ResourceEventHandler，只需实现 OnAdd OnUpdate OnDelete 方法，分别对应 informer 监听创建、更新和删除事件类型。

源码分析

1. 初始化过程

路径cmd/kube-controller-manager/app/controllermanager.go

Run方法-> CreateControllerContext -> ctx.InformerFactory.Start
初始化SharedInformerFactory，并赋值到ctx上下文中

func CreateControllerContext(s *options.CMServer, rootClientBuilder, clientBuilder controller.ControllerClientBuilder, stop <-chan struct{}) (ControllerContext, error) {
	versionedClient := rootClientBuilder.ClientOrDie("shared-informers")
	sharedInformers := informers.NewSharedInformerFactory(versionedClient, ResyncPeriod(s)())

	availableResources, err := GetAvailableResources(rootClientBuilder)
	if err != nil {
		return ControllerContext{}, err
	}

	cloud, err := cloudprovider.InitCloudProvider(s.CloudProvider, s.CloudConfigFile)
	if err != nil {
		return ControllerContext{}, fmt.Errorf("cloud provider could not be initialized: %v", err)
	}

	

	ctx := ControllerContext{
		ClientBuilder:      clientBuilder,
		InformerFactory:    sharedInformers,
		Options:            *s,
		AvailableResources: availableResources,
		Cloud:              cloud,
		Stop:               stop,
		InformersStarted:   make(chan struct{}),
	}
	return ctx, nil
}

调用SharedInformerFactory的start方法

// Start initializes all requested informers.
func (f *sharedInformerFactory) Start(stopCh <-chan struct{}) {
	f.lock.Lock()
	defer f.lock.Unlock()

	for informerType, informer := range f.informers {
		if !f.startedInformers[informerType] {
			go informer.Run(stopCh)
			f.startedInformers[informerType] = true
		}
	}
}

2. sharedIndexInformer函数

路径： client-go/tools/cache/shared_informer.go

初始化DeltaFIFO，创建queue
s.cacheMutationDetector.Run检查缓存对象是否变化
processorStopCh, s.processor.run调用Listener.run和Listener.pop，处理queue
s.controller.Run(stopCh)构建Reflector，先list然后在watch

func (s *sharedIndexInformer) Run(stopCh <-chan struct{}) {
	defer utilruntime.HandleCrash()

	fifo := NewDeltaFIFO(MetaNamespaceKeyFunc, nil, s.indexer)

	cfg := &Config{
		Queue:            fifo,
		ListerWatcher:    s.listerWatcher,
		ObjectType:       s.objectType,
		FullResyncPeriod: s.resyncCheckPeriod,
		RetryOnError:     false,
		ShouldResync:     s.processor.shouldResync,

		Process: s.HandleDeltas,
	}

	func() {
		s.startedLock.Lock()
		defer s.startedLock.Unlock()

		s.controller = New(cfg)
		s.controller.(*controller).clock = s.clock
		s.started = true
	}()

	// Separate stop channel because Processor should be stopped strictly after controller
	processorStopCh := make(chan struct{})
	var wg wait.Group
	defer wg.Wait()              // Wait for Processor to stop
	defer close(processorStopCh) // Tell Processor to stop
	wg.StartWithChannel(processorStopCh, s.cacheMutationDetector.Run)
	wg.StartWithChannel(processorStopCh, s.processor.run)

	defer func() {
		s.startedLock.Lock()
		defer s.startedLock.Unlock()
		s.stopped = true // Don't want any new listeners
	}()
	s.controller.Run(stopCh)
}

2.1 NewDeltaFIFO函数

路径：client-go/tools/cache/delta_fifo.go

DeltaFIFO可以理解生产消费的队列，Reflector为生产者

func NewDeltaFIFO(keyFunc KeyFunc, compressor DeltaCompressor, knownObjects KeyListerGetter) *DeltaFIFO {
	f := &DeltaFIFO{
		items:           map[string]Deltas{},
		queue:           []string{},
		keyFunc:         keyFunc,
		deltaCompressor: compressor,
		knownObjects:    knownObjects,
	}
	f.cond.L = &f.lock
	return f
}

2.2 CacheMutationDetector接口Run方法

defaultCacheMutationDetector实现了接口

func (d *defaultCacheMutationDetector) Run(stopCh <-chan struct{}) {
	// we DON'T want protection from panics.  If we're running this code, we want to die
	for {
		d.CompareObjects()

		select {
		case <-stopCh:
			return
		case <-time.After(d.period):
		}
	}
}

2.3 Process的run方法

调用Listener.run和Listener.pop，处理queue

func (p *sharedProcessor) run(stopCh <-chan struct{}) {
	func() {
		p.listenersLock.RLock()
		defer p.listenersLock.RUnlock()
		for _, listener := range p.listeners {
			p.wg.Start(listener.run)
			p.wg.Start(listener.pop)
		}
	}()
	<-stopCh
	p.listenersLock.RLock()
	defer p.listenersLock.RUnlock()
	for _, listener := range p.listeners {
		close(listener.addCh) // Tell .pop() to stop. .pop() will tell .run() to stop
	}
	p.wg.Wait() // Wait for all .pop() and .run() to stop
}

2.3.1 调用listener.run方法

主要是根据updateNotification addNotification deleteNotification，对应相应的函数进行处理

func (p *processorListener) run() {
	defer utilruntime.HandleCrash()

	for next := range p.nextCh {
		switch notification := next.(type) {
		case updateNotification:
			p.handler.OnUpdate(notification.oldObj, notification.newObj)
		case addNotification:
			p.handler.OnAdd(notification.newObj)
		case deleteNotification:
			p.handler.OnDelete(notification.oldObj)
		default:
			utilruntime.HandleError(fmt.Errorf("unrecognized notification: %#v", next))
		}
	}
}

2.3.3 调用listener.pop方法

func (p *processorListener) pop() {
	defer utilruntime.HandleCrash()
	defer close(p.nextCh) // Tell .run() to stop

	var nextCh chan<- interface{}
	var notification interface{}
	for {
		select {
		case nextCh <- notification:
			// Notification dispatched
			var ok bool
			notification, ok = p.pendingNotifications.ReadOne()
			if !ok { // Nothing to pop
				nextCh = nil // Disable this select case
			}
		case notificationToAdd, ok := <-p.addCh:
			if !ok {
				return
			}
			if notification == nil { // No notification to pop (and pendingNotifications is empty)
				// Optimize the case - skip adding to pendingNotifications
				notification = notificationToAdd
				nextCh = p.nextCh
			} else { // There is already a notification waiting to be dispatched
				p.pendingNotifications.WriteOne(notificationToAdd)
			}
		}
	}
}

2.4 controller的Run函数

主要是生成对象Reflector，调用其Run方法
processLoop函数

func (c *controller) Run(stopCh <-chan struct{}) {
	defer utilruntime.HandleCrash()
	go func() {
		<-stopCh
		c.config.Queue.Close()
	}()
	r := NewReflector(
		c.config.ListerWatcher,
		c.config.ObjectType,
		c.config.Queue,
		c.config.FullResyncPeriod,
	)
	r.ShouldResync = c.config.ShouldResync
	r.clock = c.clock

	c.reflectorMutex.Lock()
	c.reflector = r
	c.reflectorMutex.Unlock()

	var wg wait.Group
	defer wg.Wait()

	wg.StartWithChannel(stopCh, r.Run)

	wait.Until(c.processLoop, time.Second, stopCh)
}

2.4.1 Reflector的Run函数

Reflector主要对接kubernetes API，调用list/watch方法，更新缓存（先list所有在进行watch操作i）

// Run starts a watch and handles watch events. Will restart the watch if it is closed.
// Run will exit when stopCh is closed.
func (r *Reflector) Run(stopCh <-chan struct{}) {
	glog.V(3).Infof("Starting reflector %v (%s) from %s", r.expectedType, r.resyncPeriod, r.name)
	wait.Until(func() {
		if err := r.ListAndWatch(stopCh); err != nil {
			utilruntime.HandleError(err)
		}
	}, r.period, stopCh)
}

2.4.2 ProcessLoop主要调用HandleDeltas

func (s *sharedIndexInformer) HandleDeltas(obj interface{}) error {
	s.blockDeltas.Lock()
	defer s.blockDeltas.Unlock()

	// from oldest to newest
	for _, d := range obj.(Deltas) {
		switch d.Type {
		case Sync, Added, Updated:
			isSync := d.Type == Sync
			s.cacheMutationDetector.AddObject(d.Object)
			if old, exists, err := s.indexer.Get(d.Object); err == nil && exists {
				if err := s.indexer.Update(d.Object); err != nil {
					return err
				}
				s.processor.distribute(updateNotification{oldObj: old, newObj: d.Object}, isSync)
			} else {
				if err := s.indexer.Add(d.Object); err != nil {
					return err
				}
				s.processor.distribute(addNotification{newObj: d.Object}, isSync)
			}
		case Deleted:
			if err := s.indexer.Delete(d.Object); err != nil {
				return err
			}
			s.processor.distribute(deleteNotification{oldObj: d.Object}, false)
		}
	}
	return nil
}

【kubernetes/k8s源码分析】 client-go包之Informer源码分析