前面一篇文章对k8s informer做了概要分析，本篇文章将对informer的初始化与启动进行分析。
先来回忆一下informer的架构。
k8s client-go informer主要包括以下部件：
（1）Reflector：Reflector从kube-apiserver中list&watch资源对象，然后调用DeltaFIFO的Add/Update/Delete/Replace方法将资源对象及其变化包装成Delta并将其丢到DeltaFIFO中；
（2）DeltaFIFO：DeltaFIFO中存储着一个map和一个queue，即map[object key]Deltas以及object key的queue，Deltas为Delta的切片类型，Delta装有对象及对象的变化类型（Added/Updated/Deleted/Sync） ，Reflector负责DeltaFIFO的输入，Controller负责处理DeltaFIFO的输出；
（3）Controller：Controller从DeltaFIFO的queue中pop一个object key出来，并获取其关联的 Deltas出来进行处理，遍历Deltas，根据对象的变化更新Indexer中的本地内存缓存，并通知Processor，相关对象有变化事件发生；
（4）Processor：Processor根据对象的变化事件类型，调用相应的ResourceEventHandler来处理对象的变化；
（5）Indexer：Indexer中有informer维护的指定资源对象的相对于etcd数据的一份本地内存缓存，可通过该缓存获取资源对象，以减少对apiserver、对etcd的请求压力；
（6）ResourceEventHandler：用户根据自身处理逻辑需要，注册自定义的的ResourceEventHandler，当对象发生变化时，将触发调用对应类型的ResourceEventHandler来做处理。
... factory := informers.NewSharedInformerFactory(client, 30*time.Second) podInformer := factory.Core().V1().Pods() informer := podInformer.Informer() ... go factory.Start(stopper) ... if !cache.WaitForCacheSync(stopper, informer.HasSynced) { runtime.HandleError(fmt.Errorf("Timed out waiting for caches to sync")) return } ...上一节有列举了informer的使用代码，注意看到示例代码中的下面这段代码，做了informer初始化与启动，其中包括：
（1）informers.NewSharedInformerFactory：初始化informer factory；
（2）podInformer.Informer：初始化pod informer；
（3）factory.Start：启动informer factory；
（4）cache.WaitForCacheSync：等待list操作获取到的对象都同步到informer本地缓存Indexer中；
下面也将根据这四部分进行informer的初始化与启动分析。
先来看下sharedInformerFactory结构体，看下里面有哪些属性。
看到几个比较重要的属性：
（1）client：连接k8s的clientSet；
（2）informers：是个map，可以装各个对象的informer；
（3）startedInformers：记录已经启动的informer；
// staging/src/k8s.io/client-go/informers/factory.gotype 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}NewSharedInformerFactory方法用于初始化informer factory，主要是初始化并返回sharedInformerFactory结构体。
// staging/src/k8s.io/client-go/informers/factory.gofunc NewSharedInformerFactory(client kubernetes.Interface, defaultResync time.Duration) SharedInformerFactory { return NewSharedInformerFactoryWithOptions(client, defaultResync)}func NewFilteredSharedInformerFactory(client kubernetes.Interface, defaultResync time.Duration, namespace string, tweakListOptions internalinterfaces.TweakListOptionsFunc) SharedInformerFactory { return NewSharedInformerFactoryWithOptions(client, defaultResync, WithNamespace(namespace), WithTweakListOptions(tweakListOptions))}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}上一节有列举了informer的使用代码，注意看到示例代码中的下面这段代码，这里利用了工厂方法设计模式，podInformer.Informer()即初始化了sharedInformerFactory中的pod的informer，具体调用关系可自行看如下代码，比较简单，这里不再展开分析。
// 初始化informer factory以及pod informer factory := informers.NewSharedInformerFactory(client, 30*time.Second) podInformer := factory.Core().V1().Pods() informer := podInformer.Informer()Informer方法中调用了f.factory.InformerFor方法来做pod informer的初始化。
// k8s.io/client-go/informers/core/v1/pod.gofunc (f *podInformer) Informer() cache.SharedIndexInformer { return f.factory.InformerFor(&corev1.Pod{}, f.defaultInformer)}Informer方法中调用了f.factory.InformerFor方法来做pod informer的初始化，并传入f.defaultInformer作为newFunc，而在f.factory.InformerFor方法中，调用newFunc来初始化informer。
这里也可以看到，其实informer初始化后会存储进map f.informers[informerType]中，即存储进sharedInformerFactory结构体的informers属性中，方便共享使用。
// staging/src/k8s.io/client-go/informers/factory.gofunc (f *sharedInformerFactory) InformerFor(obj runtime.Object, newFunc internalinterfaces.NewInformerFunc) cache.SharedIndexInformer { f.lock.Lock() defer f.lock.Unlock() informerType := reflect.TypeOf(obj) informer, exists := f.informers[informerType] if exists { return informer } resyncPeriod, exists := f.customResync[informerType] if !exists { resyncPeriod = f.defaultResync } informer = newFunc(f.client, resyncPeriod) f.informers[informerType] = informer return informer}defaultInformer方法中，调用了NewFilteredPodInformer方法来初始化pod informer，最终初始化并返回sharedIndexInformer结构体。
// k8s.io/client-go/informers/core/v1/pod.gofunc (f *podInformer) defaultInformer(client kubernetes.Interface, resyncPeriod time.Duration) cache.SharedIndexInformer { return NewFilteredPodInformer(client, f.namespace, resyncPeriod, cache.Indexers{cache.NamespaceIndex: cache.MetaNamespaceIndexFunc}, f.tweakListOptions)}func NewFilteredPodInformer(client kubernetes.Interface, namespace string, resyncPeriod time.Duration, indexers cache.Indexers, tweakListOptions internalinterfaces.TweakListOptionsFunc) cache.SharedIndexInformer { return cache.NewSharedIndexInformer( &cache.ListWatch{ ListFunc: func(options metav1.ListOptions) (runtime.Object, error) { if tweakListOptions != nil { tweakListOptions(&options) } return client.CoreV1().Pods(namespace).List(options) }, WatchFunc: func(options metav1.ListOptions) (watch.Interface, error) { if tweakListOptions != nil { tweakListOptions(&options) } return client.CoreV1().Pods(namespace).Watch(options) }, }, &corev1.Pod{}, resyncPeriod, indexers, )}func NewSharedIndexInformer(lw ListerWatcher, objType runtime.Object, defaultEventHandlerResyncPeriod time.Duration, indexers Indexers) SharedIndexInformer { realClock := &clock.RealClock{} sharedIndexInformer := &sharedIndexInformer{ processor: &sharedProcessor{clock: realClock}, indexer: NewIndexer(DeletionHandlingMetaNamespaceKeyFunc, indexers), listerWatcher: lw, objectType: objType, resyncCheckPeriod: defaultEventHandlerResyncPeriod, defaultEventHandlerResyncPeriod: defaultEventHandlerResyncPeriod, cacheMutationDetector: NewCacheMutationDetector(fmt.Sprintf("%T", objType)), clock: realClock, } return sharedIndexInformer}sharedIndexInformer结构体中重点看到以下几个属性：
（1）indexer：对应着informer中的部件Indexer，Indexer中有informer维护的指定资源对象的相对于etcd数据的一份本地内存缓存，可通过该缓存获取资源对象，以减少对apiserver、对etcd的请求压力；
（2）controller：对应着informer中的部件Controller，Controller从DeltaFIFO中pop Deltas出来处理，根据对象的变化更新Indexer中的本地内存缓存，并通知Processor，相关对象有变化事件发生；
（3）processor：对应着informer中的部件Processor，Processor根据对象的变化事件类型，调用相应的ResourceEventHandler来处理对象的变化；
// staging/src/k8s.io/client-go/tools/cache/shared_informer.gotype 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}cache结构体为Indexer接口的实现；
// staging/src/k8s.io/client-go/tools/cache/store.gotype cache struct { cacheStorage ThreadSafeStore keyFunc KeyFunc}threadSafeMap struct是ThreadSafeStore接口的一个实现，其最重要的一个属性便是items了，items是用map构建的键值对，资源对象都存在items这个map中，key根据资源对象来算出，value为资源对象本身，这里的items即为informer的本地缓存了，而indexers与indices属性则与索引功能有关。
// staging/src/k8s.io/client-go/tools/cache/thread_safe_store.gotype threadSafeMap struct { lock sync.RWMutex items map[string]interface{} // indexers maps a name to an IndexFunc indexers Indexers // indices maps a name to an Index indices Indices}关于Indexer的详细分析会在后续有专门的文章做分析，这里不展开分析；
而controller结构体则包含了informer中的主要部件Reflector以及DeltaFIFO；
（1）Reflector：Reflector从kube-apiserver中list&watch资源对象，然后将对象的变化包装成Delta并将其丢到DeltaFIFO中；
（2）DeltaFIFO：DeltaFIFO存储着map[object key]Deltas以及object key的queue，Delta装有对象及对象的变化类型 ，Reflector负责DeltaFIFO的输入，Controller负责处理DeltaFIFO的输出；
// staging/src/k8s.io/client-go/tools/cache/controller.gotype controller struct { config Config reflector *Reflector reflectorMutex sync.RWMutex clock clock.Clock}type Config struct { // The queue for your objects; either a FIFO or // a DeltaFIFO. Your Process() function should accept // the output of this Queue's Pop() method. Queue ...}sharedInformerFactory.Start为informer factory的启动方法，其主要逻辑为循环遍历informers，然后跑goroutine调用informer.Run来启动sharedInformerFactory中存储的各个informer。
// staging/src/k8s.io/client-go/informers/factory.gofunc (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 } }}sharedIndexInformer.Run用于启动informer，主要逻辑为：
（1）调用NewDeltaFIFO，初始化DeltaFIFO；
（2）构建Config结构体，这里留意下Process属性，赋值了s.HandleDeltas，后面会分析到该方法；
（3）调用New，利用Config结构体来初始化controller；
（4）调用s.processor.run，启动processor；
（5）调用s.controller.Run，启动controller；
// staging/src/k8s.io/client-go/tools/cache/shared_informer.gofunc (s *sharedIndexInformer) Run(stopCh <-chan struct{}) { defer utilruntime.HandleCrash() // 初始化DeltaFIFO fifo := NewDeltaFIFO(MetaNamespaceKeyFunc, s.indexer) // 构建Config结构体 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() // 初始化controller 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) // 启动processor wg.StartWithChannel(processorStopCh, s.processor.run) defer func() { s.startedLock.Lock() defer s.startedLock.Unlock() s.stopped = true // Don't want any new listeners }() // 启动controller s.controller.Run(stopCh)}New函数初始化了controller并return。
// staging/src/k8s.io/client-go/tools/cache/controller.gofunc New(c *Config) Controller { ctlr := &controller{ config: *c, clock: &clock.RealClock{}, } return ctlr}s.processor.run启动了processor，其中注意到listener.run与listener.pop两个核心方法即可，暂时没有用到，等下面用到他们的时候再做分析。
// staging/src/k8s.io/client-go/tools/cache/shared_informer.gofunc (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) } p.listenersStarted = true }() <-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}controller.Run为controller的启动方法，这里主要看到几个点：
（1）调用NewReflector，初始化Reflector；
（2）调用r.Run，实际上是调用了Reflector的启动方法来启动Reflector；
（3）调用c.processLoop，开始controller的核心处理；
// k8s.io/client-go/tools/cache/controller.gofunc (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)}先来看到Reflector结构体，这里重点看到以下属性：
（1）expectedType：放到Store中（即DeltaFIFO中）的对象类型；
（2）store：store会赋值为DeltaFIFO，具体可以看之前的informer初始化与启动分析即可得知，这里不再展开分析；
（3）listerWatcher：存放list方法和watch方法的ListerWatcher interface实现；
// k8s.io/client-go/tools/cache/reflector.gotype Reflector struct { ... expectedType reflect.Type store Store listerWatcher ListerWatcher ...}Reflector.Run方法中启动了Reflector，而Reflector的核心处理逻辑为从kube-apiserver处做list&watch操作，然后将得到的对象封装存储进DeltaFIFO中。
// staging/src/k8s.io/client-go/tools/cache/reflector.gofunc (r *Reflector) Run(stopCh <-chan struct{}) { klog.V(3).Infof("Starting reflector %v (%s) from %s", r.expectedTypeName, r.resyncPeriod, r.name) wait.Until(func() { if err := r.ListAndWatch(stopCh); err != nil { utilruntime.HandleError(err) } }, r.period, stopCh)}controller的核心处理方法processLoop中，最重要的逻辑是循环调用c.config.Queue.Pop将DeltaFIFO中的队头元素给pop出来，然后调用c.config.Process方法来做处理，当处理出错时，再调用c.config.Queue.AddIfNotPresent将对象重新加入到DeltaFIFO中去。
// k8s.io/client-go/tools/cache/controller.gofunc (c *controller) processLoop() { for { obj, err := c.config.Queue.Pop(PopProcessFunc(c.config.Process)) if err != nil { if err == ErrFIFOClosed { return } if c.config.RetryOnError { // This is the safe way to re-enqueue. c.config.Queue.AddIfNotPresent(obj) } } }}根据前面sharedIndexInformer.Run方法的分析中可以得知，c.config.Process其实就是sharedIndexInformer.HandleDeltas。
HandleDeltas方法中，将从DeltaFIFO中pop出来的对象以及类型，相应的在indexer中做添加、更新、删除操作，并调用s.processor.distribute通知自定义的ResourceEventHandler。
// staging/src/k8s.io/client-go/tools/cache/shared_informer.gofunc (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}怎么通知到自定义的ResourceEventHandler呢？继续往下看。
可以看到distribute方法最终是将构造好的addNotification、updateNotification、deleteNotification对象写入到p.addCh中。
// staging/src/k8s.io/client-go/tools/cache/shared_informer.gofunc (p *sharedProcessor) distribute(obj interface{}, sync bool) { p.listenersLock.RLock() defer p.listenersLock.RUnlock() if sync { for _, listener := range p.syncingListeners { listener.add(obj) } } else { for _, listener := range p.listeners { listener.add(obj) } }}func (p *processorListener) add(notification interface{}) { p.addCh <- notification}到这里，processor中的listener.pop以及listener.run方法终于派上了用场，继续往下看。
分析processorListener的pop方法可以得知，其逻辑实际上就是将p.addCh中的对象给拿出来，然后丢进了p.nextCh中。那么谁来处理p.nextCh呢？继续往下看。
// staging/src/k8s.io/client-go/tools/cache/shared_informer.gofunc (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) } } }}在processorListener的run方法中，将循环读取p.nextCh，判断对象类型，是updateNotification则调用p.handler.OnUpdate方法，是addNotification则调用p.handler.OnAdd方法，是deleteNotification则调用p.handler.OnDelete方法做处理。
// staging/src/k8s.io/client-go/tools/cache/shared_informer.gofunc (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: %T", 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)}而p.handler.OnUpdate、p.handler.OnAdd、p.handler.OnDelete方法实际上就是自定义的的ResourceEventHandlerFuncs了。
informer.AddEventHandler(cache.ResourceEventHandlerFuncs{ AddFunc: onAdd, UpdateFunc: onUpdate, DeleteFunc: onDelete, })// staging/src/k8s.io/client-go/tools/cache/controller.gotype ResourceEventHandlerFuncs struct { AddFunc func(obj interface{}) UpdateFunc func(oldObj, newObj interface{}) DeleteFunc func(obj interface{})}func (r ResourceEventHandlerFuncs) OnAdd(obj interface{}) { if r.AddFunc != nil { r.AddFunc(obj) }}func (r ResourceEventHandlerFuncs) OnUpdate(oldObj, newObj interface{}) { if r.UpdateFunc != nil { r.UpdateFunc(oldObj, newObj) }}func (r ResourceEventHandlerFuncs) OnDelete(obj interface{}) { if r.DeleteFunc != nil { r.DeleteFunc(obj) }}可以看出在cache.WaitForCacheSync方法中，实际上是调用方法入参cacheSyncs ...InformerSynced来判断cache是否同步完成（即调用informer.HasSynced方法），而这里说的cache同步完成，意思是等待informer从kube-apiserver同步资源完成，即informer的list操作获取的对象都存入到informer中的indexer本地缓存中；
// staging/src/k8s.io/client-go/tools/cache/shared_informer.gofunc WaitForCacheSync(stopCh <-chan struct{}, cacheSyncs ...InformerSynced) bool { err := wait.PollImmediateUntil(syncedPollPeriod, func() (bool, error) { for _, syncFunc := range cacheSyncs { if !syncFunc() { return false, nil } } return true, nil }, stopCh) if err != nil { klog.V(2).Infof("stop requested") return false } klog.V(4).Infof("caches populated") return true}HasSynced方法实际上是调用了sharedIndexInformer.controller.HasSynced方法；
// staging/src/k8s.io/client-go/tools/cache/shared_informer.gofunc (s *sharedIndexInformer) HasSynced() bool { s.startedLock.Lock() defer s.startedLock.Unlock() if s.controller == nil { return false } return s.controller.HasSynced()}这里的c.config.Queue.HasSynced()方法，实际上是指DeltaFIFO的HasSynced方法，会在DeltaFIFO的分析中再详细分析，这里只需要知道当informer的list操作获取的对象都存入到informer中的indexer本地缓存中则返回true即可；
// staging/src/k8s.io/client-go/tools/cache/controller.gofunc (c *controller) HasSynced() bool { return c.config.Queue.HasSynced()}可以顺带看下sharedInformerFactory.WaitForCacheSync方法，其实际上是遍历factory中的所有informer，调用cache.WaitForCacheSync，然后传入每个informer的HasSynced方法作为入参；
// staging/src/k8s.io/client-go/informers/factory.gofunc (f *sharedInformerFactory) WaitForCacheSync(stopCh <-chan struct{}) map[reflect.Type]bool { informers := func() map[reflect.Type]cache.SharedIndexInformer { f.lock.Lock() defer f.lock.Unlock() informers := map[reflect.Type]cache.SharedIndexInformer{} for informerType, informer := range f.informers { if f.startedInformers[informerType] { informers[informerType] = informer } } return informers }() res := map[reflect.Type]bool{} for informType, informer := range informers { res[informType] = cache.WaitForCacheSync(stopCh, informer.HasSynced) } return res}至此，整个informer的初始化与启动的分析就结束了，后面会对informer中的各个核心部件进行详细分析，敬请期待。
下面用两张图片总结一下informer的初始化与启动；
