kubernetes v1.12:?https://github.com/kubernetes/kubernetes

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。

?

sharedInformerFactory结构体

? ? ?路径client-go/informers/factory.go

• customResync:?每种Informer自定义的同步周期
• TweakListOptionsFunc func(*v1.ListOptions)：?函数指针，用来调整list选项（第3章节讲解）
• informers: 缓存每一种informer
• startedInformers: 用于开启跟踪

type sharedInformerFactory struct {
	client           kubernetes.Interface
	namespace        string
	tweakListOptions internalinterfaces.TweakListOptionsFunc
	lock             sync.Mutex
	defaultResync    time.Duration
	customResync     map[reflect.Type]time.Duration

	informers map[reflect.Type]cache.SharedIndexInformer
	// startedInformers is used for tracking which informers have been started.
	// This allows Start() to be called multiple times safely.
	startedInformers map[reflect.Type]bool
}

?

SharedIndexInformer接口

? ??sharedIndexInformer实现了该接口

type SharedIndexInformer interface {
   SharedInformer
   // AddIndexers add indexers to the informer before it starts.
   AddIndexers(indexers Indexers) error
   GetIndexer() Indexer
}

?

1. 初始化过程

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

• ? Run方法->?CreateControllerContext -> ctx.InformerFactory.Start

?

2.?CreateControllerContext函数

// CreateControllerContext creates a context struct containing references to resources needed by the
// controllers such as the cloud provider and clientBuilder. rootClientBuilder is only used for
// the shared-informers client and token controller.
func CreateControllerContext(s *config.CompletedConfig, rootClientBuilder, clientBuilder controller.ControllerClientBuilder, stop <-chan struct{}) (ControllerContext, error) {
	versionedClient := rootClientBuilder.ClientOrDie("shared-informers")

? ? 2.1?NewSharedInformerFactoryWithOptions函数

? ? ?调用 NewSharedInformerFactory -> NewSharedInformerFactoryWithOptions

? ? ?创建sharedInformerFactory实例

// NewSharedInformerFactoryWithOptions constructs a new instance of a SharedInformerFactory with additional options.
func NewSharedInformerFactoryWithOptions(client kubernetes.Interface, defaultResync time.Duration, options ...SharedInformerOption) SharedInformerFactory {
	factory := &sharedInformerFactory{
		client:           client,
		namespace:        v1.NamespaceAll,
		defaultResync:    defaultResync,
		informers:        make(map[reflect.Type]cache.SharedIndexInformer),
		startedInformers: make(map[reflect.Type]bool),
		customResync:     make(map[reflect.Type]time.Duration),
	}

	// Apply all options
	for _, opt := range options {
		factory = opt(factory)
	}

	return factory
}

? ? 2.2 填充ControllerContext上下文

? ? ? ?初始化SharedInformerFactory，并赋值到ctx上下文中

	// Use a discovery client capable of being refreshed.
	discoveryClient := rootClientBuilder.ClientOrDie("controller-discovery")
	cachedClient := cacheddiscovery.NewMemCacheClient(discoveryClient.Discovery())
	restMapper := restmapper.NewDeferredDiscoveryRESTMapper(cachedClient)
	go wait.Until(func() {
		restMapper.Reset()
	}, 30*time.Second, stop)

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

	cloud, loopMode, err := createCloudProvider(s.ComponentConfig.KubeCloudShared.CloudProvider.Name, s.ComponentConfig.KubeCloudShared.ExternalCloudVolumePlugin,
		s.ComponentConfig.KubeCloudShared.CloudProvider.CloudConfigFile, s.ComponentConfig.KubeCloudShared.AllowUntaggedCloud, sharedInformers)
	if err != nil {
		return ControllerContext{}, err
	}

	ctx := ControllerContext{
		ClientBuilder:      clientBuilder,
		InformerFactory:    sharedInformers,
		ComponentConfig:    s.ComponentConfig,
		RESTMapper:         restMapper,
		AvailableResources: availableResources,
		Cloud:              cloud,
		LoopMode:           loopMode,
		Stop:               stop,
		InformersStarted:   make(chan struct{}),
		ResyncPeriod:       ResyncPeriod(s),
	}

?

3.??TweakListOptionsFunc

? ? ?掉整的参数有namespace?tweakListOptions?customResync，设置list过滤选项

// WithCustomResyncConfig sets a custom resync period for the specified informer types.
func WithCustomResyncConfig(resyncConfig map[v1.Object]time.Duration) SharedInformerOption {
	return func(factory *sharedInformerFactory) *sharedInformerFactory {
		for k, v := range resyncConfig {
			factory.customResync[reflect.TypeOf(k)] = v
		}
		return factory
	}
}

// WithTweakListOptions sets a custom filter on all listers of the configured SharedInformerFactory.
func WithTweakListOptions(tweakListOptions internalinterfaces.TweakListOptionsFunc) SharedInformerOption {
	return func(factory *sharedInformerFactory) *sharedInformerFactory {
		factory.tweakListOptions = tweakListOptions
		return factory
	}
}

// WithNamespace limits the SharedInformerFactory to the specified namespace.
func WithNamespace(namespace string) SharedInformerOption {
	return func(factory *sharedInformerFactory) *sharedInformerFactory {
		factory.namespace = namespace
		return factory
	}
}

?

4. sharedInformerFactory Start方法

? ? ? Run函数中调用SharedInformerFactory的start方法（controllerContext.InformerFactory.Start(controllerContext.Stop)）

// 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
		}
	}
}

? ? 4.1 sharedIndexInformer结构体

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

type sharedIndexInformer struct {
	indexer    Indexer
	controller Controller

	processor             *sharedProcessor
	cacheMutationDetector CacheMutationDetector

	// This block is tracked to handle late initialization of the controller
	listerWatcher ListerWatcher
	objectType    runtime.Object

	// resyncCheckPeriod is how often we want the reflector's resync timer to fire so it can call
	// shouldResync to check if any of our listeners need a resync.
	resyncCheckPeriod time.Duration
	// defaultEventHandlerResyncPeriod is the default resync period for any handlers added via
	// AddEventHandler (i.e. they don't specify one and just want to use the shared informer's default
	// value).
	defaultEventHandlerResyncPeriod time.Duration
	// clock allows for testability
	clock clock.Clock

	started, stopped bool
	startedLock      sync.Mutex

	// blockDeltas gives a way to stop all event distribution so that a late event handler
	// can safely join the shared informer.
	blockDeltas sync.Mutex
}

? ? 4.2?sharedIndexInformer Run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()

? ? 4.2.1 NewDeltaFIFO函数

? ? 路径：client-go/tools/cache/delta_fifo.go，第5章节讲解DeltaFIFO

• 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
}

? ? 4.2.2 创建Config实例

? ?包括DletaFIFO队列，list watch，处理函数HandleDeltas等，创建controller实例

	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
	}()

? ? 4.2.3?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):
		}
	}
}

? ? 4.2.4?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
}

? ? 4.2.4.1 listener run方法

func (p *processorListener) run() {
	// this call blocks until the channel is closed.  When a panic happens during the notification
	// we will catch it, **the offending item will be skipped!**, and after a short delay (one second)
	// the next notification will be attempted.  This is usually better than the alternative of never
	// delivering again.
	stopCh := make(chan struct{})
	wait.Until(func() {
		// this gives us a few quick retries before a long pause and then a few more quick retries
		err := wait.ExponentialBackoff(retry.DefaultRetry, func() (bool, error) {
			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))
				}
			}
			// the only way to get here is if the p.nextCh is empty and closed
			return true, nil
		})

		// the only way to get here is if the p.nextCh is empty and closed
		if err == nil {
			close(stopCh)
		}
	}, 1*time.Minute, stopCh)
}

? ? ?4.2.4.2 controller Run函数

? ? ?路径 clieng/tools/cache/controller.go

? ? ?初始化Reflector实例（第6章节讲解）

// Run begins processing items, and will continue until a value is sent down stopCh.
// It's an error to call Run more than once.
// Run blocks; call via go.
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)
}

?

?

? 2.3.1?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
}

?

5.?DeltaFIFO

? ? 5.1 DeltaFIFO结构体

? ? ? 生产消费者队列，用来存储 Watch API 返回的各种事件

• queue: 实现了先入先出功能，存储对象的键值
• items: kv存储方式

type DeltaFIFO struct {
	// We depend on the property that items in the set are in
	// the queue and vice versa, and that all Deltas in this
	// map have at least one Delta.
	items map[string]Deltas
	queue []string

	// populated is true if the first batch of items inserted by Replace() has been populated
	// or Delete/Add/Update was called first.
	populated bool
	// initialPopulationCount is the number of items inserted by the first call of Replace()
	initialPopulationCount int

	// keyFunc is used to make the key used for queued item
	// insertion and retrieval, and should be deterministic.
	keyFunc KeyFunc

	// knownObjects list keys that are "known", for the
	// purpose of figuring out which items have been deleted
	// when Replace() or Delete() is called.
	knownObjects KeyListerGetter
}

? ? 5.2 DeltaFIFO方法

• func (f *DeltaFIFO) Add(obj interface{}) error
• func (f *DeltaFIFO) Update(obj interface{}) error
• func (f *DeltaFIFO) List() []interface{}
• func (f *DeltaFIFO) Delete(obj interface{}) error
• func (f *DeltaFIFO) Get(obj interface{}) (item interface{}, exists bool, err error)
• func (f *DeltaFIFO) Pop(process PopProcessFunc) (interface{}, error)

? ??

6.?Reflector

? ? 6.1 Reflector结构体

? ? ? ?路径 client-go/tools/cache/reflector.go

? ? ??监听通过controller中的Reflector实现，主要作用是通过 Kubernetes Watch API 监听某种 resource 下的所有事件

// Reflector watches a specified resource and causes all changes to be reflected in the given store.
type Reflector struct {
	// name identifies this reflector. By default it will be a file:line if possible.
	name string
	// metrics tracks basic metric information about the reflector
	metrics *reflectorMetrics

	// The type of object we expect to place in the store.
	expectedType reflect.Type
	// The destination to sync up with the watch source
	store Store
	// listerWatcher is used to perform lists and watches.
	listerWatcher ListerWatcher
	// period controls timing between one watch ending and
	// the beginning of the next one.

}

? ? 6.2?Reflector Run方法

? ? ? ?开启List watch机制

// 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)
}

?

7 ListAndWatch函数

? ? ? ?通过资源版本list所有item，然后调用watch

// ListAndWatch first lists all items and get the resource version at the moment of call,
// and then use the resource version to watch.
// It returns error if ListAndWatch didn't even try to initialize watch.
func (r *Reflector) ListAndWatch(stopCh <-chan struct{}) error {
	glog.V(3).Infof("Listing and watching %v from %s", r.expectedType, r.name)
	var resourceVersion string

? ? 7.1?syncWith

? ? ? 使用deltaFIFO的Replace全量替换

// syncWith replaces the store's items with the given list.
func (r *Reflector) syncWith(items []runtime.Object, resourceVersion string) error {
	found := make([]interface{}, 0, len(items))
	for _, item := range items {
		found = append(found, item)
	}
	return r.store.Replace(found, resourceVersion)
}

? ? 7.2 watchHandler

? ? ? 监听资源新版本的增量变化

// watchHandler watches w and keeps *resourceVersion up to date.
func (r *Reflector) watchHandler(w watch.Interface, resourceVersion *string, errc chan error, stopCh <-chan struct{}) error {
	start := r.clock.Now()
	eventCount := 0

	// Stopping the watcher should be idempotent and if we return from this function there's no way
	// we're coming back in with the same watch interface.
	defer w.Stop()
	// update metrics
	defer func() {
		r.metrics.numberOfItemsInWatch.Observe(float64(eventCount))
		r.metrics.watchDuration.Observe(time.Since(start).Seconds())
	}()

? ? ?7.2.1 从chan中读取对象，使用反射机制

	for {
		select {
		case <-stopCh:
			return errorStopRequested
		case err := <-errc:
			return err
		case event, ok := <-w.ResultChan():
			if !ok {
				break loop
			}
			if event.Type == watch.Error {
				return apierrs.FromObject(event.Object)
			}
			if e, a := r.expectedType, reflect.TypeOf(event.Object); e != nil && e != a {
				utilruntime.HandleError(fmt.Errorf("%s: expected type %v, but watch event object had type %v", r.name, e, a))
				continue
			}
			meta, err := meta.Accessor(event.Object)
			if err != nil {
				utilruntime.HandleError(fmt.Errorf("%s: unable to understand watch event %#v", r.name, event))
				continue
			}
			newResourceVersion := meta.GetResourceVersion()

? ? ?7.2.2 更具事件类型，对deltaFIFO调用其方法，更新版本并记录当前的版本，也就是在watch，将从这个版本的next开始

			switch event.Type {
			case watch.Added:
				err := r.store.Add(event.Object)
				if err != nil {
					utilruntime.HandleError(fmt.Errorf("%s: unable to add watch event object (%#v) to store: %v", r.name, event.Object, err))
				}
			case watch.Modified:
				err := r.store.Update(event.Object)
				if err != nil {
					utilruntime.HandleError(fmt.Errorf("%s: unable to update watch event object (%#v) to store: %v", r.name, event.Object, err))
				}
			case watch.Deleted:
				// TODO: Will any consumers need access to the "last known
				// state", which is passed in event.Object? If so, may need
				// to change this.
				err := r.store.Delete(event.Object)
				if err != nil {
					utilruntime.HandleError(fmt.Errorf("%s: unable to delete watch event object (%#v) from store: %v", r.name, event.Object, err))
				}
			default:
				utilruntime.HandleError(fmt.Errorf("%s: unable to understand watch event %#v", r.name, event))
			}
			*resourceVersion = newResourceVersion
			r.setLastSyncResourceVersion(newResourceVersion)

?

?

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