k8s replicaset controller源码分析（2）-核心处理逻辑分析

replicaset controller分析

replicaset controller简介

replicaset controller是kube-controller-manager组件中众多控制器中的一个，是 replicaset 资源对象的控制器，其通过对replicaset、pod 2种资源的监听，当这2种资源发生变化时会触发 replicaset controller 对相应的replicaset对象进行调谐操作，从而完成replicaset期望副本数的调谐，当实际pod的数量未达到预期时创建pod，当实际pod的数量超过预期时删除pod。

replicaset controller主要作用是根据replicaset对象所期望的pod数量与现存pod数量做比较，然后根据比较结果创建/删除pod，最终使得replicaset对象所期望的pod数量与现存pod数量相等。

replicaset controller架构图

replicaset controller的大致组成和处理流程如下图，replicaset controller对pod和replicaset对象注册了event handler，当有事件时，会watch到然后将对应的replicaset对象放入到queue中，然后syncReplicaSet方法为replicaset controller调谐replicaset对象的核心处理逻辑所在，从queue中取出replicaset对象，做调谐处理。

replicaset controller分析分为3大块进行，分别是：
（1）replicaset controller初始化和启动分析；
（2）replicaset controller核心处理逻辑分析；
（3）replicaset controller expectations机制分析。

本篇博客进行replicaset controller核心处理逻辑分析。

replicaset controller核心处理逻辑分析

基于v1.17.4

经过前面分析的replicaset controller的初始化与启动，知道了replicaset controller监听replicaset、pod对象的add、update与delete事件，然后对replicaset对象做相应的调谐处理，这里来接着分析replicaset controller的调谐处理（核心处理）逻辑，从rsc.syncHandler作为入口进行分析。

rsc.syncHandler

rsc.syncHandler即rsc.syncReplicaSet方法，主要逻辑：
（1）获取replicaset对象以及关联的pod对象列表；
（2）调用rsc.expectations.SatisfiedExpectations，判断上一轮对replicaset期望副本的创删操作是否完成，也可以认为是判断上一次对replicaset对象的调谐操作中，调用的rsc.manageReplicas方法是否执行完成；
（3）如果上一轮对replicaset期望副本的创删操作已经完成，且replicaset对象的DeletionTimestamp字段为nil，则调用rsc.manageReplicas做replicaset期望副本的核心调谐处理，即创删pod；
（4）调用calculateStatus计算replicaset的status，并更新。

// 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))
	}()

	namespace, name, err := cache.SplitMetaNamespaceKey(key)
	if err != nil {
		return err
	}
	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
	}

	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.
	allPods, err := rsc.podLister.Pods(rs.Namespace).List(labels.Everything())
	if err != nil {
		return err
	}
	// Ignore inactive pods.
	filteredPods := controller.FilterActivePods(allPods)

	// NOTE: filteredPods are pointing to objects from cache - if you need to
	// modify them, you need to copy it first.
	filteredPods, err = rsc.claimPods(rs, selector, filteredPods)
	if err != nil {
		return err
	}

	var manageReplicasErr error
	if rsNeedsSync && rs.DeletionTimestamp == nil {
		manageReplicasErr = rsc.manageReplicas(filteredPods, rs)
	}
	rs = rs.DeepCopy()
	newStatus := calculateStatus(rs, filteredPods, manageReplicasErr)

	// Always updates status as pods come up or die.
	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
	}
	// Resync the ReplicaSet after MinReadySeconds as a last line of defense to guard against clock-skew.
	if manageReplicasErr == nil && updatedRS.Spec.MinReadySeconds > 0 &&
		updatedRS.Status.ReadyReplicas == *(updatedRS.Spec.Replicas) &&
		updatedRS.Status.AvailableReplicas != *(updatedRS.Spec.Replicas) {
		rsc.queue.AddAfter(key, time.Duration(updatedRS.Spec.MinReadySeconds)*time.Second)
	}
	return manageReplicasErr
}

1 rsc.expectations.SatisfiedExpectations

该方法主要是判断上一轮对replicaset期望副本的创删操作是否完成，也可以认为是判断上一次对replicaset对象的调谐操作中，调用的rsc.manageReplicas方法是否执行完成。待上一次创建删除pod的操作完成后，才能进行下一次的rsc.manageReplicas方法调用。

若某replicaset对象的调谐中从未调用过rsc.manageReplicas方法，或上一轮调谐时创建/删除pod的数量已达成或调用rsc.manageReplicas后已达到超时期限（超时时间5分钟），则返回true，代表上一次创建删除pod的操作完成，可以进行下一次的rsc.manageReplicas方法调用，否则返回false。

expectations记录了replicaset对象在某一次调谐中期望创建/删除的pod数量，pod创建/删除完成后，该期望数会相应的减少，当期望创建/删除的pod数量小于等于0时，说明上一次调谐中期望创建/删除的pod数量已经达到，返回true。

关于Expectations机制后面会做详细分析。

// pkg/controller/controller_utils.go
func (r *ControllerExpectations) SatisfiedExpectations(controllerKey string) bool {
	if exp, exists, err := r.GetExpectations(controllerKey); exists {
		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 {
			klog.V(4).Infof("Controller still waiting on expectations %#v", exp)
			return false
		}
	} else if err != nil {
		klog.V(2).Infof("Error encountered while checking expectations %#v, forcing sync", err)
	} else {
		// When a new controller is created, it doesn't have expectations.
		// When it doesn't see expected watch events for > TTL, the expectations expire.
		//	- In this case it wakes up, creates/deletes controllees, and sets expectations again.
		// When it has satisfied expectations and no controllees need to be created/destroyed > TTL, the expectations expire.
		//	- In this case it continues without setting expectations till it needs to create/delete controllees.
		klog.V(4).Infof("Controller %v either never recorded expectations, or the ttl expired.", controllerKey)
	}
	// Trigg