## Kubernetes Reflector ##

Reflector is a key components for Kubernetes clients, kube-scheduler and Replication Controller.
Reflector is in the middle between client and Kubernetes API-server.

#### Definition of Reflector ####
Here is the definition of Reflector.
![reflector define](https://cloud.githubusercontent.com/assets/27221807/26737893/1bc26ccc-479a-11e7-8291-f3551d5c2e6c.png)

As shown in the definition, there are two important compoents of a Reflector:
 - **ListerWatcher**
 
   It provides two functions: *List* and *Watch*. These two functions will call API-server, and get the Events.
   
 - **Store**
 
   It is usually a in-memory storage, such as HashMap, or Queue(for FIFO). Reflector will add the Events into this Store.
   
   
Also, It should be noted that the **reflect.Type** is usually a Kind of Kubernetes Object, such as Pod, Node.

#### Example Usage of Reflector ####
Before going deeper into the implementation of Reflector, let's have a look at how Reflector can be used from a example.
This example will watch the changes(including ADD, DELETE, MODIFY) of all the Pods in the Kubernetes cluster, and print out the changes.  In addition, it will also print all the names every 30 seconds.
```go
func main() {
	client := getKubeClient()
	if client == nil {
		fmt.Println("failed to get kubeclient")
		return
	}

	stopCh := make(chan struct{})
	store := cache.NewStore(cache.MetaNamespaceKeyFunc)

	//selector := fields.SelectorFromSet(nil)
	selector := fields.Everything()
	namespace := ""
	listWatch := cache.NewListWatchFromClient(client.CoreV1Client.RESTClient(),
		"pods",
		namespace,
		selector)

	r := cache.NewReflector(listWatch, &v1.Pod{}, store, 0)

	r.RunUntil(stopCh)

	for i := 1; i < 20; i++ {
		time.Sleep(30 * time.Second)
		printContent(store.ListKeys())
	}

	time.Sleep(10 * time.Second)
	printContent(store.ListKeys())
	close(stopCh)
}
 
```