Kubernetes源碼學習-Controller-P4-ReplicaSet-Controller

P4-ReplicaSet Controller

前言

在上一篇文章中，對deployment controller的工作模式進行了詳細地分析:
Controller-P3-Deployment Controller

分析後得知，deployment controller更多的是對每個相應版本的replicaset副本數進行管理，而不涉及直接對pod的管理，因此，承接上節，本章來分析replicaSet Controller的源碼.

ReplicaSet Controller

初始化

參照上節一樣，直接來到各類controller初始化的函數:

cmd/kube-controller-manager/app/controllermanager.go:343

controllers["replicaset"] = startReplicaSetController

==> cmd/kube-controller-manager/app/apps.go:69

	go replicaset.NewReplicaSetController(
    // replicaSet controller只關注ReplicaSets和Pod這兩種資源。
		ctx.InformerFactory.Apps().V1().ReplicaSets(),
		ctx.InformerFactory.Core().V1().Pods(),
		ctx.ClientBuilder.ClientOrDie("replicaset-controller"),
		replicaset.BurstReplicas,
	).Run(int(ctx.ComponentConfig.ReplicaSetController.ConcurrentRSSyncs), ctx.Stop)

創建ReplicaSetController

先來看看NewReplicaSetController創建的過程:

==> pkg/controller/replicaset/replica_set.go:109

func NewReplicaSetController(rsInformer appsinformers.ReplicaSetInformer, podInformer coreinformers.PodInformer, kubeClient clientset.Interface, burstReplicas int) *ReplicaSetController {
	eventBroadcaster := record.NewBroadcaster()
	eventBroadcaster.StartLogging(klog.Infof)
	eventBroadcaster.StartRecordingToSink(&v1core.EventSinkImpl{Interface: kubeClient.CoreV1().Events("")})
  // NewBaseController方法往下看
	return NewBaseController(rsInformer, podInformer, kubeClient, burstReplicas,
		apps.SchemeGroupVersion.WithKind("ReplicaSet"),
		"replicaset_controller",
		"replicaset",
		controller.RealPodControl{
			KubeClient: kubeClient,
			Recorder:   eventBroadcaster.NewRecorder(scheme.Scheme, v1.EventSource{Component: "replicaset-controller"}),
		},
	)
}

// NewBaseController is the implementation of NewReplicaSetController with additional injected
// parameters so that it can also serve as the implementation of NewReplicationController.
func NewBaseController(rsInformer appsinformers.ReplicaSetInformer, podInformer coreinformers.PodInformer, kubeClient clientset.Interface, burstReplicas int,
	gvk schema.GroupVersionKind, metricOwnerName, queueName string, podControl controller.PodControlInterface) *ReplicaSetController {
	if kubeClient != nil && kubeClient.CoreV1().RESTClient().GetRateLimiter() != nil {
		metrics.RegisterMetricAndTrackRateLimiterUsage(metricOwnerName, kubeClient.CoreV1().RESTClient().GetRateLimiter())
	}

	rsc := &ReplicaSetController{
		GroupVersionKind: gvk,
		kubeClient:       kubeClient,
		podControl:       podControl,
		burstReplicas:    burstReplicas,
		expectations:     controller.NewUIDTrackingControllerExpectations(controller.NewControllerExpectations()),
		queue:            workqueue.NewNamedRateLimitingQueue(workqueue.DefaultControllerRateLimiter(), queueName),
	}

	rsInformer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc:    rsc.enqueueReplicaSet,
		UpdateFunc: rsc.updateRS,
		DeleteFunc: rsc.enqueueReplicaSet,
	})
	rsc.rsLister = rsInformer.Lister()
  // informer會同步待操作的資源到本地的queue中，HasSynced方法就是用來判斷判斷queue是否已同步的
	rsc.rsListerSynced = rsInformer.Informer().HasSynced

	podInformer.Informer().AddEventHandler(cache.ResourceEventHandlerFuncs{
		AddFunc: rsc.addPod,
		UpdateFunc: rsc.updatePod,
		DeleteFunc: rsc.deletePod,
	})
	rsc.podLister = podInformer.Lister()
  // informer會同步待操作的資源到本地的queue中，HasSynced方法就是用來判斷判斷queue是否已同步的
	rsc.podListerSynced = podInformer.Informer().HasSynced

	rsc.syncHandler = rsc.syncReplicaSet

	return rsc
}

NewBaseController這裏主要關注AddEventHandler爲資源的informer增加的curd方法，例如pod相關的addPod、updatePod、deletePod方法。

ReplicaSetController Run方法

接着往下，創建好ReplicaSetController對象後，看它的運行過程，即Run方法。

==> pkg/controller/replicaset/replica_set.go:177

// Run begins watching and syncing.
func (rsc *ReplicaSetController) Run(workers int, stopCh <-chan struct{}) {
	defer utilruntime.HandleCrash()
	defer rsc.queue.ShutDown()

	controllerName := strings.ToLower(rsc.Kind)
	klog.Infof("Starting %v controller", controllerName)
	defer klog.Infof("Shutting down %v controller", controllerName)
  
  // 判斷各個informer的緩存是否已經同步完畢的函數
	if !controller.WaitForCacheSync(rsc.Kind, stopCh, rsc.podListerSynced, rsc.rsListerSynced) {
		return
	}
  // worker的數量默認是5個，開啓5個worker，每個worker間隔1s運行一次rsc.worker函數，來檢查並收斂rs的狀態
	for i := 0; i < workers; i++ {
		go wait.Until(rsc.worker, time.Second, stopCh)
	}

	<-stopCh
}

來到了這裏，可發現ReplicaSetController.Run()函數和上一節的DeploymentController.Run()函數非常地相似。所以，從這裏開始，各類controller之間代碼相似的步驟可能會跳過，不再每個地方都重複詳細說明。

往上溯源，可以找到，worker的數量配置默認爲5個，參見這裏:

pkg/controller/apis/config/v1alpha1/defaults.go:219

func SetDefaults_ReplicaSetControllerConfiguration(obj *kubectrlmgrconfigv1alpha1.ReplicaSetControllerConfiguration) {
	if obj.ConcurrentRSSyncs == 0 {
		obj.ConcurrentRSSyncs = 5
	}
}

wait.Until()函數是很有意思的，上節也做過仔細分析，可以再回顧一下這裏:

[waituntil循環計時器函數](https://github.com/yinwenqin/kubeSourceCodeNote/blob/master/controller/Kubernetes源碼學習-Controller-P3-Controller分類與Deployment Controller.md#waituntil循環計時器函數)

好，直接進入主題，開始分析rsc.worker工作函數.

工作邏輯

pkg/controller/replicaset/replica_set.go:190

	for i := 0; i < workers; i++ {
		go wait.Until(rsc.worker, time.Second, stopCh)
	}		

==> pkg/controller/replicaset/replica_set.go:432

// processNextWorkItem()函數的作用是把informer work queue工作隊列裏的對象取出，按照申明的要求來處理它們，標記它們。
func (rsc *ReplicaSetController) worker() {
	for rsc.processNextWorkItem() {
	}
}

==> pkg/controller/replicaset/replica_set.go:437

func (rsc *ReplicaSetController) processNextWorkItem() bool {
  // work queue中取出隊首元素
	key, quit := rsc.queue.Get()
	if quit {
		return false
	}
	defer rsc.queue.Done(key)
  // syncHandler每一個隊列對象，強保證同一時間只會有一個go協程處理它(無併發競爭)。所謂sync，意思是將work queue中待操作的對象，同步實現到運行環境中。
	err := rsc.syncHandler(key.(string))
	if err == nil {
		rsc.queue.Forget(key)
		return true
	}

	utilruntime.HandleError(fmt.Errorf("Sync %q failed with %v", key, err))
	rsc.queue.AddRateLimited(key)

	return true
}

主要函數是這個syncHandler，接着追溯，可以在這裏找到這個結構體屬性函數的賦值：

pkg/controller/replicaset/replica_set.go:163

// NewBaseController is the implementation of NewReplicaSetController with additional injected
// parameters so that it can also serve as the implementation of NewReplicationController.
func NewBaseController(rsInformer appsinformers.ReplicaSetInformer, podInformer coreinformers.PodInformer, kubeClient clientset.Interface, burstReplicas int,
	gvk schema.GroupVersionKind, metricOwnerName, queueName string, podControl controller.PodControlInterface) *ReplicaSetController {
  // ... 省略
	rsc.syncHandler = rsc.syncReplicaSet

	return rsc
}

接着便可以找到ReplicaSetController.syncReplicaSet函數：

pkg/controller/replicaset/replica_set.go:562

// syncReplicaSet will sync the ReplicaSet with the given key if it has had its expectations fulfilled,
// meaning it did not expect to see any more of its pods created or deleted. This function is not meant to be
// invoked concurrently with the same key.
func (rsc *ReplicaSetController) syncReplicaSet(key string) error {

	startTime := time.Now()
	defer func() {
		klog.V(4).Infof("Finished syncing %v %q (%v)", rsc.Kind, key, time.Since(startTime))
	}()
  // key的字符串格式是這樣的: ${NAMESPACE}/${NAME}
	namespace, name, err := cache.SplitMetaNamespaceKey(key)
	if err != nil {
		return err
	}
  // 獲取到rs對象
	rs, err := rsc.rsLister.ReplicaSets(namespace).Get(name)
	if errors.IsNotFound(err) {
		klog.V(4).Infof("%v %v has been deleted", rsc.Kind, key)
		rsc.expectations.DeleteExpectations(key)
		return nil
	}
	if err != nil {
		return err
	}
  
  // 判斷rs是否實現所聲明的期望狀態，這裏SatisfiedExpectations是使用expectations機制來判斷這個rs是否滿足期望狀態。
	rsNeedsSync := rsc.expectations.SatisfiedExpectations(key)
	selector, err := metav1.LabelSelectorAsSelector(rs.Spec.Selector)
	if err != nil {
		utilruntime.HandleError(fmt.Errorf("Error converting pod selector to selector: %v", err))
		return nil
	}

	// list all pods to include the pods that don't match the rs`s selector
	// anymore but has the stale controller ref.
	// TODO: Do the List and Filter in a single pass, or use an index.
  // 取出所有的的pod，labels.Everything()取到的是空selector，即不使用label selector，取全部pod
	allPods, err := rsc.podLister.Pods(rs.Namespace).List(labels.Everything())
	if err != nil {
		return err
	}
  
	// Ignore inactive pods.
  // 去除 inactive狀態的pod
	filteredPods := controller.FilterActivePods(allPods)

  
  // 根據rs和selector來選擇受此rs版本管理的pod
	filteredPods, err = rsc.claimPods(rs, selector, filteredPods)
	if err != nil {
		return err
	}
  
  
	var manageReplicasErr error
  // 如果rs未達到期望狀態，則對副本進行管理，以使rs滿足聲明的期望狀態
	if rsNeedsSync && rs.DeletionTimestamp == nil {
    // 最重要的函數manageReplicas，未達期望時，管理rs對應的pod(新增/刪除)
		manageReplicasErr = rsc.manageReplicas(filteredPods, rs)
	}
  
	rs = rs.DeepCopy()
	newStatus := calculateStatus(rs, filteredPods, manageReplicasErr)
  
  // 只要有對應pod的更新，則需要更新rs的status字段
	updatedRS, err := updateReplicaSetStatus(rsc.kubeClient.AppsV1().ReplicaSets(rs.Namespace), rs, newStatus)
	if err != nil {
		// Multiple things could lead to this update failing. Requeuing the replica set ensures
		// Returning an error causes a requeue without forcing a hotloop
		return err
	}

  // 當指定了MinReadySeconds時，即使pod 已經是ready狀態了，但也不會視爲Available，需要等待MinReadySeconds後再來刷新rs的狀態。因此，enqueueReplicaSetAfter方法，異步等待MinReadySeconds後，把該rs重新壓入work queue隊列中
	if manageReplicasErr == nil && updatedRS.Spec.MinReadySeconds > 0 &&
		updatedRS.Status.ReadyReplicas == *(updatedRS.Spec.Replicas) &&
		updatedRS.Status.AvailableReplicas != *(updatedRS.Spec.Replicas) {
		rsc.enqueueReplicaSetAfter(updatedRS, time.Duration(updatedRS.Spec.MinReadySeconds)*time.Second)
	}
	return manageReplicasErr
}

劃重點，兩個重要的函數：SatisfiedExpectations(判斷是否滿足sync條件) / manageReplicas(sync後續的副本pod新增、刪除操作)。分別來看看

SatisfiedExpectations函數

在此之前，必須先了解一下rs controller(後面簡稱rsc)的Expectations機制。rsc會將每一個rs的期望狀態(比如期望新增3個副本)保存在本地緩存中，在sync執行之前，會對期望狀態進行條件判斷，滿足條件纔會真正進行sync操作。

來看看SatisfiedExpectations函數的邏輯：

pkg/controller/controller_utils.go:181

func (r *ControllerExpectations) SatisfiedExpectations(controllerKey string) bool {
  // 若此key存在Expectations期望狀態
	if exp, exists, err := r.GetExpectations(controllerKey); exists {
    // Expectations期望狀態達成或者過期，則需要sync
		if exp.Fulfilled() {
			klog.V(4).Infof("Controller expectations fulfilled %#v", exp)
			return true
		} else if exp.isExpired() {
			klog.V(4).Infof("Controller expectations expired %#v", exp)
			return true
		} else {
      // 存在期望狀態但未達成，則無需sync。因爲後面的handler在處理資源增刪的時候會來新建和修改Expectations，說明當前正在接近期望狀態中，所以本次無需再sync
			klog.V(4).Infof("Controller still waiting on expectations %#v", exp)
			return false
		}
	} 
  // 不存在Expectations(新增的資源對象)，或者獲取Expectations出錯，則視爲需要執行sync
    else if err != nil {
		klog.V(2).Infof("Error encountered while checking expectations %#v, forcing sync", err)
	} else {
		klog.V(4).Infof("Controller %v either never recorded expectations, or the ttl expired.", controllerKey)
	}

	return true
}

manageReplicas函數

==> pkg/controller/replicaset/replica_set.go:459

func (rsc *ReplicaSetController) manageReplicas(filteredPods []*v1.Pod, rs *apps.ReplicaSet) error {
   // rs當前管理的pod數量 與 rs聲明指定pod的數量 的差量
   diff := len(filteredPods) - int(*(rs.Spec.Replicas))
   rsKey, err := controller.KeyFunc(rs)
   if err != nil {
      utilruntime.HandleError(fmt.Errorf("Couldn't get key for %v %#v: %v", rsc.Kind, rs, err))
      return nil
   }
   // 當 rs當前管理的pod數量 小於 rs聲明指定pod的數量 時，說明應該繼續增加pod
   if diff < 0 {
      diff *= -1
      // 每次新增數量以突發增加數量burstReplicas爲上限
      if diff > rsc.burstReplicas {
         diff = rsc.burstReplicas
      }
      // 創建ExpectCreations期望
      rsc.expectations.ExpectCreations(rsKey, diff)
      klog.V(2).Infof("Too few replicas for %v %s/%s, need %d, creating %d", rsc.Kind, rs.Namespace, rs.Name, *(rs.Spec.Replicas), diff)
     
      // slowStartBatch用來以指數級批量啓動pod, 其中controller.SlowStartInitialBatchSize默認值爲1，作爲底數。
      successfulCreations, err := slowStartBatch(diff, controller.SlowStartInitialBatchSize, func() error {
         // 創建單個pod的函數 CreatePodsWithControllerRef
         err := rsc.podControl.CreatePodsWithControllerRef(rs.Namespace, &rs.Spec.Template, rs, metav1.NewControllerRef(rs, rsc.GroupVersionKind))
         if err != nil && errors.IsTimeout(err) {

            return nil
         }
         return err
      })


      if skippedPods := diff - successfulCreations; skippedPods > 0 {
         klog.V(2).Infof("Slow-start failure. Skipping creation of %d pods, decrementing expectations for %v %v/%v", skippedPods, rsc.Kind, rs.Namespace, rs.Name)
         for i := 0; i < skippedPods; i++ {
            // Decrement the expected number of creates because the informer won't observe this pod
            rsc.expectations.CreationObserved(rsKey)
         }
      }
      return err
     
     // 當 rs當前管理的pod數量 大於 rs聲明指定pod的數量 時，說明應該減少pod
   } else if diff > 0 {
      if diff > rsc.burstReplicas {
         diff = rsc.burstReplicas
      }
      klog.V(2).Infof("Too many replicas for %v %s/%s, need %d, deleting %d", rsc.Kind, rs.Namespace, rs.Name, *(rs.Spec.Replicas), diff)

      // 獲取需要刪除的pod
      podsToDelete := getPodsToDelete(filteredPods, diff)
      // 修改rs的期望狀態，在期望中剔除將要刪除的pod
      rsc.expectations.ExpectDeletions(rsKey, getPodKeys(podsToDelete))

      errCh := make(chan error, diff)
      var wg sync.WaitGroup
      wg.Add(diff)
      // 併發刪除目標pod
      for _, pod := range podsToDelete {
         go func(targetPod *v1.Pod) {
            defer wg.Done()
            if err := rsc.podControl.DeletePod(rs.Namespace, targetPod.Name, rs); err != nil {
               // Decrement the expected number of deletes because the informer won't observe this deletion
               podKey := controller.PodKey(targetPod)
               klog.V(2).Infof("Failed to delete %v, decrementing expectations for %v %s/%s", podKey, rsc.Kind, rs.Namespace, rs.Name)
               rsc.expectations.DeletionObserved(rsKey, podKey)
               errCh <- err
            }
         }(pod)
      }
      wg.Wait()

      select {
      case err := <-errCh:
         // all errors have been reported before and they're likely to be the same, so we'll only return the first one we hit.
         if err != nil {
            return err
         }
      default:
      }
   }

   return nil
}

這個函數即是實際操控管理pod副本數量的函數，其中的slowStartBatch批量啓動pod的功能比較有意思，來看看。

批量啓動pod

pkg/controller/replicaset/replica_set.go:658

func slowStartBatch(count int, initialBatchSize int, fn func() error) (int, error) {
   // 剩餘要執行的數量
   remaining := count
   // 累計成功執行的數量
   successes := 0
  // batchSize是每次批量執行的數量，從initialBatchSize(1)和剩餘數量中取最小值。每次循環執行成功後，batchSize乘以2，以指數級擴充。
   for batchSize := integer.IntMin(remaining, initialBatchSize); batchSize > 0; batchSize = integer.IntMin(2*batchSize, remaining) {
      errCh := make(chan error, batchSize)
      var wg sync.WaitGroup
      wg.Add(batchSize)
      for i := 0; i < batchSize; i++ {
         go func() {
            defer wg.Done()
            if err := fn(); err != nil {
               errCh <- err
            }
         }()
      }
      wg.Wait()
      curSuccesses := batchSize - len(errCh)
      successes += curSuccesses
      // 某一輪循環出錯時，跳出循環，後續的不再執行。
      if len(errCh) > 0 {
         return successes, <-errCh
      }
      remaining -= batchSize
   }
   return successes, nil
}

ReplicaSetController工作流程總結

總結一下，在出現新版本的rs後，rsc按照以下步驟進行工作：

1.通過SatisfiedExpectations函數，發現expectations期望狀態本地緩存中不存在此rs key，因此返回true，需要sync

2.通過manageReplicas管理pod，新增或刪除

3.判斷pod副本數是多了還是少了，多則要刪，少則要增

4.增刪之前創建expectations對象並設置add / del值

5.slowStartBatch新增 / 併發刪除 pod

6.更新expection

expections緩存機制，在運行的pod副本數在向聲明指定的副本數收斂之時，很好地避免了頻繁的informer數據查詢，以及可能隨之而來的數據更新不及時的問題，這個機制設計巧妙貫穿整個rsc工作過程，也是不太易於理解之處。