Kubernetes 中 Informer 的使用

// staging/src/k8s.io/apimachinery/pkg/watch/watch.go
// Interface 可以被任何知道如何 watch 和通知变化的对象实现
type Interface interface {
  // Stops watching. Will close the channel returned by ResultChan(). Releases
  // any resources used by the watch.
  Stop()
  // Returns a chan which will receive all the events. If an error occurs
  // or Stop() is called, this channel will be closed, in which case the
  // watch should be completely cleaned up.
  ResultChan() <-chan Event
}
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// staging/src/k8s.io/apimachinery/pkg/watch/watch.go
// EventType 定义可能的事件类型
type EventType string

const (
  Added    EventType = "ADDED"
  Modified EventType = "MODIFIED"
  Deleted  EventType = "DELETED"
  Bookmark EventType = "BOOKMARK"
  Error    EventType = "ERROR"

  DefaultChanSize int32 = 100
)
// Event represents a single event to a watched resource.
// +k8s:deepcopy-gen=true
type Event struct {
  Type EventType
  // Object is:
  //  * If Type is Added or Modified: the new state of the object.
  //  * If Type is Deleted: the state of the object immediately before deletion.
  //  * If Type is Bookmark: the object (instance of a type being watched) where
  //    only ResourceVersion field is set. On successful restart of watch from a
  //    bookmark resourceVersion, client is guaranteed to not get repeat event
  //    nor miss any events.
  //  * If Type is Error: *api.Status is recommended; other types may make sense
  //    depending on context.
  Object runtime.Object
}
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package main

import (
  "flag"
  "fmt"
  "path/filepath"
  "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/rest"
  "k8s.io/client-go/tools/cache"
  "k8s.io/client-go/tools/clientcmd"
  "k8s.io/client-go/util/homedir"
)
func main() {
  var err error
  var config *rest.Config

  var kubeconfig *string

  if home := homedir.HomeDir(); home != "" {
    kubeconfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "[可选] kubeconfig 绝对路径")
  } else {
    kubeconfig = flag.String("kubeconfig", "", "kubeconfig 绝对路径")
  }
  // 初始化 rest.Config 对象
  if config, err = rest.InClusterConfig(); err != nil {
    if config, err = clientcmd.BuildConfigFromFlags("", *kubeconfig); err != nil {
      panic(err.Error())
    }
  }
  // 创建 Clientset 对象
  clientset, err := kubernetes.NewForConfig(config)
  if err != nil {
    panic(err.Error())
  }
  // 初始化 informer factory（为了测试方便这里设置每30s重新 List 一次）
  informerFactory := informers.NewSharedInformerFactory(clientset, time.Second*30)
  // 对 Deployment 监听
  deployInformer := informerFactory.Apps().V1().Deployments()
  // 创建 Informer（相当于注册到工厂中去，这样下面启动的时候就会去 List & Watch 对应的资源）
  informer := deployInformer.Informer()
  // 创建 Lister
  deployLister := deployInformer.Lister()
  // 注册事件处理程序
  informer.AddEventHandler(cache.ResourceEventHandlerFuncs{
    AddFunc:    onAdd,
    UpdateFunc: onUpdate,
    DeleteFunc: onDelete,
  })
  stopper := make(chan struct{})
  defer close(stopper)

  // 启动 informer，List & Watch
  informerFactory.Start(stopper)
  // 等待所有启动的 Informer 的缓存被同步
  informerFactory.WaitForCacheSync(stopper)
  // 从本地缓存中获取 default 中的所有 deployment 列表
  deployments, err := deployLister.Deployments("default").List(labels.Everything())
  if err != nil {
    panic(err)
  }
  for idx, deploy := range deployments {
    fmt.Printf("%d -> %s\n", idx+1, deploy.Name)
  }
  <-stopper
}
func onAdd(obj interface{}) {
  deploy := obj.(*v1.Deployment)
  fmt.Println("add a deployment:", deploy.Name)
}
func onUpdate(old, new interface{}) {
  oldDeploy := old.(*v1.Deployment)
  newDeploy := new.(*v1.Deployment)
  fmt.Println("update deployment:", oldDeploy.Name, newDeploy.Name)
}
func onDelete(obj interface{}) {
  deploy := obj.(*v1.Deployment)
  fmt.Println("delete a deployment:", deploy.Name)
}
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$ go run main.go
add a deployment: dingtalk-hook
add a deployment: spin-orca
add a deployment: argocd-server
add a deployment: istio-egressgateway
add a deployment: vault-agent-injector
add a deployment: rook-ceph-osd-0
add a deployment: rook-ceph-osd-2
add a deployment: code-server
......
1 -> nginx
2 -> helloworld-v1
3 -> productpage-v1
4 -> details-v1
......
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