什么是informers？

informers是k8s一种重要的通知机制, 通过list&watch来监听变更事.

示例代码：

监听deployment变化

import (
	"fmt"
	"time"

	v1 "k8s.io/api/apps/v1"
	"k8s.io/apimachinery/pkg/labels"
	"k8s.io/client-go/informers"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/tools/cache"
	"sigs.k8s.io/controller-runtime/pkg/client/config"
)
func main() {
	conf, err := config.GetConfig()
	if err != nil {
		fmt.Println("error")
		panic(err.Error())
	}
	clientset, err := kubernetes.NewForConfig(conf)
	if err != nil {
		fmt.Println("error")
		panic(err.Error())
	}
	//获取informers
	informersFactory := informers.NewSharedInformerFactory(clientset, 30*time.Second)
	//获取deployInformer
	deployInformer := informersFactory.Apps().V1().Deployments()
	informer := deployInformer.Informer()
	deployLister := deployInformer.Lister()
	if err != nil {
		fmt.Println("error")
		panic(err.Error())
	}
	informer.AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc:    create,
		UpdateFunc: update,
		DeleteFunc: delete,
	})
	stopper := make(chan struct{})

	defer close(stopper)
	//开启list & watch 机制
	informersFactory.Start(stopper)
	//等待缓存队列更新
	informersFactory.WaitForCacheSync(stopper)

	deploys, err := deployLister.Deployments("default").List(labels.Everything())
	if err != nil {
		panic(err.Error())
	}
	for _, v := range deploys {
		fmt.Println("deploy is ", v.Name)
	}
	<-stopper
}

func update(oldObj, newObj interface{}) {
	fmt.Println("old ", oldObj.(*v1.Deployment).Name, "update replicas at", oldObj.(*v1.Deployment).Status.Replicas)
	fmt.Println("new ", oldObj.(*v1.Deployment).Name, " update replicas at", newObj.(*v1.Deployment).Status.Replicas)
}

func delete(obj interface{}) {
	fmt.Println("delete at ", obj.(*v1.Deployment).Name)
}

func create(obj interface{}) {
	fmt.Println("create at ", obj.(*v1.Deployment).Name)
}

运行

新建一个deploy监听变化

控制日志，看见nginx已经被创建了，并且副本数已经从0改成1

更新deploy

$ kubectl edit deploy nginx 
deployment.apps/nginx edited

删除deploy, 也被正常监听到了

总结：

list&watch是k8s动态更新通知的重要渠道, 我们不止可以监听k8s内置资源,也可以监听自定义资源.

注：k8内置资源对象大概以下几种

类别	名称
资源对象	Pod、ReplicaSet、ReplicationController、Deployment、StatefulSet、 DaemonSet、Job、CronJob、HorizontalPodAutoscaling、Node、 Namespace、Service、Ingress、Label、CustomResourceDefinition
存储对象	Volume、PersistentVolume、Secret、ConfigMap
策略对象	SecurityContext、ResourceQuota、LimitRange
身份对象	ServiceAccount、Role、ClusterRole

Q.E.D.