Kubernetes Client-go Informer 源码分析

几乎所有的Controller manager 和CRD Controller 都会使用Client-go 的Informer 函数，这样通过Watch 或者Get List 可以获取对应的Object，下面我们从源码分析角度来看一下Client go Informer 的机制。

kubeClient, err := kubernetes.NewForConfig(cfg)
if err != nil {
    klog.Fatalf("Error building kubernetes clientset: %s", err.Error())
}

kubeInformerFactory := kubeinformers.NewSharedInformerFactory(kubeClient, time.Second*30)

controller := NewController(kubeClient, exampleClient,
    kubeInformerFactory.Apps().V1().Deployments(),
    exampleInformerFactory.Samplecontroller().V1alpha1().Foos())

// notice that there is no need to run Start methods in a separate goroutine. (i.e. go kubeInformerFactory.Start(stopCh)
// Start method is non-blocking and runs all registered informers in a dedicated goroutine.
kubeInformerFactory.Start(stopCh)

这里的例子是以https://github.com/kubernetes/sample-controller/blob/master/main.go节选，主要以 k8s 默认的Deployment Informer 为例子。可以看到直接使用Client-go Informer 还是非常简单的，先不管NewCOntroller函数里面执行了什么，顺着代码来看一下kubeInformerFactory.Start 都干了啥。

// Start initializes all requested informers.
func (f *sharedInformerFactory) Start(stopCh