深入分析Kubernetes DaemonSet Controller

Author: xidianwangtao@gmail.com | Version: Kubernetes 1.13

摘要：DaemonSet是Kubernetes中用户最常用的对象之一，我们用它来部署Nodes上守护应用，比如日志组件、节点监控组件等。从用户的使用角度来讲，DaemonSet看似简单，但实际上它涉及的点非常多，比如DaemonSet Pod满足什么条件才能在Node上运行、Node出现MemoryPressure或者其他异常Condition时是否能运行、调度的逻辑是怎样的、滚动更新的逻辑是怎样的等等，本文讲从DaemonSet Controller的源码着手，分析其中关键逻辑。

DaemonSet Controller

DaemonSet Controller Struct

DaemonSet Controller的核心结构包括：

• burstReplcas int: 每次sync时，Create和Delete Pods的数量上限，代码中写死为250。
• queue workqueue.RateLimitingInterface: 存放待同步DaemonSet Key(namespaces/name)的Delaying Queue。
• syncHandler func(dsKey string) error: 负责同步DaemonSet Queue中对象，包括Replicas管理、UpdateStrategy升级、更新DaemonSet Status等工作，是DaemonSet Controller中最核心的逻辑。
• expectations controller.ControllerExpectationsInterface: 维护每个DaemonSet对象每次Sync期望Create/Delete Pods数的TTLCache。
• suspendedDaemonPods map[string]sets.String: key为NodeName，value是DaemonSet集合，这些DaemonSet包含该Node上'wantToRun & !shouldSchedule'的Pod。
  • wantToRun: 为True，当DaemonSet Controller去Simulate调度时，Predicate（主要是GeneralPredicates和PodToleratesNodeTaints）时忽略如下PredicateFailureError（都是些资源类的Error）时成功，有其他PredicateFailureError为False。如果DaemonSet的Spec中指定了NodeName，则根据其是否与node.Name匹配成功来决定wantToRun的值。
    • ErrDiskConflict;
    • ErrVolumeZoneConflict;
    • ErrMaxVolumeCountExceeded;
    • ErrNodeUnderMemoryPressure;
    • ErrNodeUnderDiskPressure;
    • InsufficientResourceError;
  • shouldSchedule:
    • 如果DaemonSet的Spec中指定了NodeName，则根据其是否与node.Name匹配成功来决定shouldSchedule的值。
    • 如果Predicate时出现所有类型的PredicateFailureError之一，则shouldSchedule都为false。
    • 如果出现InsufficientResourceError，则shouldSchedule也为false。
• failedPodsBackoff *flowcontrol.Backoff: DaemonSet Controller Run时会启动一个协程，每隔2*MaxDuration(2*15Min)会强制进行一次failedPods GC清理。每次syncDaemonSet处理该删除的Pods时，会按照1s,2s,4s,8s,.....15min的Backoff机制做一定的delay处理，实现流控的效果。防止kubelet拒绝某些DaemonSet Pods后，马上又被拒绝，如此就会出现很多无效的循环，因此加入了Backoff机制。

DaemonSet Controller的创建和启动

NewDaemonSetsController负责创建Controller，其中很重要的工作就是注册以下Informer的EventHandler：

• daemonSetInformer: AddFunc/DeleteFunc/UpdateFunc最终其实都主要是enqueue DaemonSet；
• historyInformer:
  • AddFunc: addHistory;
  • UpdateFunc: updateHistory;
  • DeleteFunc: deleteHistory;
• podInformer:
  • AddFunc: addPod;
  • UpdateFunc: updatePod;
  • DeleteFunc: deletePod;
• nodeInformer:
  • AddFunc: addNode;
  • UpdateFunc: updateNode;

DamonSet Controller Run启动时，主要干两件事：

• 启动2个workers协程，每个worker负责从queue中取DaemonSet Key进行sync。

• 启动1个failedPodsBackoff GC协程，每隔1Min清理一次集群中所有DaemonSet/Node对应的Failed Pods。

只有deletePod时，才会requeueSuspendedDaemonPods。-- 为什么？

DaemonSet的同步

worker会从queue中取待同步的DamonSet Key，调用syncDaemonSet完成自动管理，syncDaemonSet是DaemonSet管理的核心入口。

pkg/controller/daemon/daemon_controller.go:1208 func (dsc *DaemonSetsController) syncDaemonSet(key string) error { ... ds, err := dsc.dsLister.DaemonSets(namespace).Get(name) if errors.IsNotFound(err) { klog.V(3).Infof("daemon set has been deleted %v", key) dsc.expectations.DeleteExpectations(key) return nil } if err != nil { return fmt.Errorf("unable to retrieve ds %v from store: %v", key, err) } everything := metav1.LabelSelector{} if reflect.DeepEqual(ds.Spec.Selector, &everything) { dsc.eventRecorder.Eventf(ds, v1.EventTypeWarning, SelectingAllReason, "This daemon set is selecting all pods. A non-empty selector is required.") return nil } // Don't process a daemon set until all its creations and deletions have been processed. // For example if daemon set foo asked for 3 new daemon pods in the previous call to manage, // then we do not want to call manage on foo until the daemon pods have been created. ... if ds.DeletionTimestamp != nil { return nil } // Construct histories of the DaemonSet, and get the hash of current history cur, old, err := dsc.constructHistory(ds) if err != nil { return fmt.Errorf("failed to construct revisions of DaemonSet: %v", err) } hash := cur.Labels[apps.DefaultDaemonSetUniqueLabelKey] if !dsc.expectations.SatisfiedExpectations(dsKey) { // Only update status. Don't raise observedGeneration since controller didn't process object of that generation. return dsc.updateDaemonSetStatus(ds, hash, false) } err = dsc.manage(ds, hash) if err != nil { return err } // Process rolling updates if we're ready. if dsc.expectations.SatisfiedExpectations(dsKey) { switch ds.Spec.UpdateStrategy.Type { case apps.OnDeleteDaemonSetStrategyType: case apps.RollingUpdateDaemonSetStrategyType: err = dsc.rollingUpdate(ds, hash) } if err != nil { return err } } err = dsc.cleanupHistory(ds, old) if err != nil { return fmt.Errorf("failed to clean up revisions of DaemonSet: %v", err) } return dsc.updateDaemonSetStatus(ds, hash, true) } 

核心的流程如下：

• 首先检查该DaemonSet对象在本地Store中是否被删除，如果是，则从expectations中删除该DaemonSet对应的数据。
• 检查该DaemonSet对象的LabelSelector是否为空，如果是，则syncDaemonSet返回结束，不进行同步，那么DaemonSet对应的Pod也不会被创建了。
• 如果其DeletionTimestamp非空，意味着用户触发了删除，则syncDaemonSet返回结束，不进行同步。DaemonSet对应的Pod交由GC Controller去完成删除。
• 然后constructHistory获取该DaemonSet的Current ControllerRevision和所有Old ControllerRevisions，并确保所有ControllerRevisions都打上Label: "controller-revision-hash: ControllerRevision.Name"，更新Current ControllerRevision的Revision = maxRevision(old) + 1。
• 检查当前expectations是否已经满足，当不满足时，只更新DaemonSet Status，同步流程结束。
  • expectations中add和del都不大于0，表示Controller expectations已经实现，则当前expectations已经满足。
  • expectations已经超时，超时时间是5min（不可配置），如果超时，则表示需要进行同步。
  • 如果expectations中还没有该DaemonSet的信息，则表示也满足了，将触发DaemonSet同步。
  • 此处updateDaemonSetStatus会更新该Daemonset.Status的如下字段，注意不会更新ObservedGeneration（也没发生变化）。
    • DesiredNumberScheduled：用户期望调度的DaemonSet Pods数量，对应前面提到的wantToRun为true的pods数量。
    • CurrentNumberScheduled：用户期望调度的，并且当前已经运行在Node上的Pods数量。
    • NumberMisscheduled：用户不期望调度的（wantToRun为false），并且已经运行在对应Node上Pods数量，即已经错误调度的Pods数量。
    • NumberReady：CurrentNumberScheduled中，Pod Type Ready Condition为true的Pods数量。
    • UpdatedNumberScheduled：CurrentNumberScheduled中，Pod Label controller-revision-hash对应的hash值与Current ControllerRevision的该hash值相等的Pods数量，即Pod Template已经更新的Pods数量。
    • NumberAvailable：CurrentNumberScheduled中，Pod Type Ready Condition为true，并且Available（Ready时间超过minReadySeconds）的Pods数量。
    • NumberUnavailable：desiredNumberScheduled - numberAvailable。
• 调用manage进行DaemonSet Pod的管理：计算待删除和创建的Pod列表，然后调用syncNodes分批次(1,2,4,8,..)的完成Pod的创建和删除。如果syncNodes之前发现某些Node上对应DaemonSet Pod是Failed，那么syncNodes后返回error。syncNode会将expectations中的add/del都归零甚至负数，只有这样，才会在syncDaemonSet中调用manage进行Pod管理。
• 如果manage返回error，则syncDaemonSet流程结束。否则会继续下面的流程。
• 检查当前expectations是否已经满足，如果满足，则根据UpdateStrategy触发DaemonSet更新：
  • 如果UpdateStrategy是OnDelete，则等待用户delete Pod，触发对应的DaemonSet的enqueue，在syncNodes时更新最新的Pod Template创建新Pod。
  • 如果UpdateStrategy是RollingUpdate，则调用rollingUpdate进行滚动更新，后面会详细分析。
• 如果DaemonSet更新成功，则根据需要（Old ControllerRevisions数量是否超过Spec.RevisionHistoryLimit，默认为10）清理超过RevisionHistoryLimit的最老的ControllerRevisions。
• updateDaemonSetStatus会更新该Daemonset.Status，跟前面不同的是，这里还需要更新Status.ObservedGeneration。

DaemonSet Pod的调度

在Kubernetes 1.12之前的版本中，默认由DaemonSet Controller完成Daemon Pods的调度工作，即由DaemonSet Controller给待调度Pod的spec.nodeName设置值，然后对应Node的kubelet watch到该事件，再在本节点创建DaemonSet Pod。在Kubernetes 1.12+，默认启用了ScheduleDaemonSetPods FeatureGate, DaemonSet的调度就交由default scheduler完成。

DamonSet Pods Should Be On Node

在manage daemonset时，通过调用podsShouldBeOnNode来计算出希望在该Node上启动的DaemonSet Pods(nodesNeedingDaemonPods)、希望在该Node上删除的DaemonSet Pods(podsToDelete)，以及在该Node上已经Failed DamonSetPods数量，然后在syncNodes中根据这三个信息，去创建、删除对应的Pods。

func (dsc *DaemonSetsController) manage(ds *apps.DaemonSet, hash string) error { // Find out the pods which are created for the nodes by DaemonSet. nodeToDaemonPods, err := dsc.getNodesToDaemonPods(ds) ... for _, node := range nodeList { nodesNeedingDaemonPodsOnNode, podsToDeleteOnNode, failedPodsObservedOnNode, err := dsc.podsShouldBeOnNode( node, nodeToDaemonPods, ds) if err != nil { continue } nodesNeedingDaemonPods = append(nodesNeedingDaemonPods, nodesNeedingDaemonPodsOnNode...) podsToDelete = append(podsToDelete, podsToDeleteOnNode...) failedPodsObserved += failedPodsObservedOnNode } // Label new pods using the hash label value of the current history when creating them if err = dsc.syncNodes(ds, podsToDelete, nodesNeedingDaemonPods, hash); err != nil { return err } ... return nil } 

podsShouldBeOnNode是如何计算出nodesNeedingDaemonPods、podsToDelete、failedPodsObserved的呢？—— 通过调用nodeShouldRunDaemonPod(node *v1.Node, ds *apps.DaemonSet)计算出如下三个状态值：

• wantToRun: 当DaemonSet Controller去Simulate调度时，Predicate（主要是GeneralPredicates和PodToleratesNodeTaints）时忽略如下PredicateFailureError（都是些资源类的Error）时为True，有其他PredicateFailureError为False。如果DaemonSet的Spec中指定了NodeName，则根据其是否与node.Name匹配成功来决定wantToRun的值。 - ErrDiskConflict; - ErrVolumeZoneConflict; - ErrMaxVolumeCountExceeded; - ErrNodeUnderMemoryPressure; - ErrNodeUnderDiskPressure; - InsufficientResourceError;
• shouldSchedule:
  - 如果DaemonSet的Spec中指定了NodeName，则根据其是否与node.Name匹配成功来决定shouldSchedule的值。 - 如果Predicate时出现所有类型的PredicateFailureError之一，则shouldSchedule都为false。 - 如果出现InsufficientResourceError，则shouldSchedule也为false。
• failedPodsBackoff *flowcontrol.Backoff: 按照1s,2s,4s,8s,...的backoff周期去处理（删除重建）Failed DaemonSet Pods，实现流控的效果。DaemonSet Controller Run时会启动一个协程，每隔2*MaxDuration(2*15Min)会强制进行一次failedPods GC清理。

• shouldContinueRunning，如下情况之一出现，则该值为false，其他情况为true。
  • ErrNodeSelectorNotMatch,
  • ErrPodNotMatchHostName,
  • ErrNodeLabelPresenceViolated,
  • ErrPodNotFitsHostPorts:
  • ErrTaintsTolerationsNotMatch，如果是No Execute类型的Taint/Toleration匹配，则为true，否则为false，也就是说会忽略NoExecute类型的Taint/Toleration匹配。
  • ErrPodAffinityNotMatch,
  • ErrServiceAffinityViolated，
  • unknown predicate failure reason

然后根据这三个状态值，得到nodesNeedingDaemonPods []string、podsToDelete []string、failedPodsObserved int。

// podsShouldBeOnNode figures out the DaemonSet pods to be created and deleted on the given node: func (dsc *DaemonSetsController) podsShouldBeOnNode( node *v1.Node, nodeToDaemonPods map[string][]*v1.Pod, ds *apps.DaemonSet, ) (nodesNeedingDaemonPods, podsToDelete []string, failedPodsObserved int, err error) { wantToRun, shouldSchedule, shouldContinueRunning, err := dsc.nodeShouldRunDaemonPod(node, ds) if err != nil { return } daemonPods, exists := nodeToDaemonPods[node.Name] dsKey, _ := cache.MetaNamespaceKeyFunc(ds) dsc.removeSuspendedDaemonPods(node.Name, dsKey) switch { case wantToRun && !shouldSchedule: // If daemon pod is supposed to run, but can not be scheduled, add to suspended list. dsc.addSuspendedDaemonPods(node.Name, dsKey) case shouldSchedule && !exists: // If daemon pod is supposed to be running on node, but isn't, create daemon pod. nodesNeedingDaemonPods = append(nodesNeedingDaemonPods, node.Name) case shouldContinueRunning: // If a daemon pod failed, delete it // If there's non-daemon pods left on this node, we will create it in the next sync loop var daemonPodsRunning []*v1.Pod for _, pod := range daemonPods { if pod.DeletionTimestamp != nil { continue } if pod.Status.Phase == v1.PodFailed { failedPodsObserved++ // This is a critical place where DS is often fighting with kubelet that rejects pods. // We need to avoid hot looping and backoff. backoffKey := failedPodsBackoffKey(ds, node.Name) now := dsc.failedPodsBackoff.Clock.Now() inBackoff := dsc.failedPodsBackoff.IsInBackOffSinceUpdate(backoffKey, now) if inBackoff { delay := dsc.failedPodsBackoff.Get(backoffKey) klog.V(4).Infof("Deleting failed pod %s/%s on node %s has been limited by backoff - %v remaining", pod.Namespace, pod.Name, node.Name, delay) dsc.enqueueDaemonSetAfter(ds, delay) continue } dsc.failedPodsBackoff.Next(backoffKey, now) msg := fmt.Sprintf("Found failed daemon pod %s/%s on node %s, will try to kill it", pod.Namespace, pod.Name, node.Name) klog.V(2).Infof(msg) // Emit an event so that it's discoverable to users. dsc.eventRecorder.Eventf(ds, v1.EventTypeWarning, FailedDaemonPodReason, msg) podsToDelete = append(podsToDelete, pod.Name) } else { daemonPodsRunning = append(daemonPodsRunning, pod) } } // If daemon pod is supposed to be running on node, but more than 1 daemon pod is running, delete the excess daemon pods. // Sort the daemon pods by creation time, so the oldest is preserved. if len(daemonPodsRunning) > 1 { sort.Sort(podByCreationTimestampAndPhase(daemonPodsRunning)) for i := 1; i < len(daemonPodsRunning); i++ { podsToDelete = append(podsToDelete, daemonPodsRunning[i].Name) } } case !shouldContinueRunning && exists: // If daemon pod isn't supposed to run on node, but it is, delete all daemon pods on node. for _, pod := range daemonPods { podsToDelete = append(podsToDelete, pod.Name) } } return nodesNeedingDaemonPods, podsToDelete, failedPodsObserved, nil } // nodeShouldRunDaemonPod checks a set of preconditions against a (node,daemonset) and returns a summary. func (dsc *DaemonSetsController) nodeShouldRunDaemonPod(node *v1.Node, ds *apps.DaemonSet) (wantToRun, shouldSchedule, shouldContinueRunning bool, err error) { newPod := NewPod(ds, node.Name) // Because these bools require an && of all their required conditions, we start // with all bools set to true and set a bool to false if a condition is not met. // A bool should probably not be set to true after this line. wantToRun, shouldSchedule, shouldContinueRunning = true, true, true // If the daemon set specifies a node name, check that it matches with node.Name. if !(ds.Spec.Template.Spec.NodeName == "" || ds.Spec.Template.Spec.NodeName == node.Name) { return false, false, false, nil } reasons, nodeInfo, err := dsc.simulate(newPod, node, ds) if err != nil { klog.Warningf("DaemonSet Predicates failed on node %s for ds '%s/%s' due to unexpected error: %v", node.Name, ds.ObjectMeta.Namespace, ds.ObjectMeta.Name, err) return false, false, false, err } // TODO(k82cn): When 'ScheduleDaemonSetPods' upgrade to beta or GA, remove unnecessary check on failure reason, // e.g. InsufficientResourceError; and simplify "wantToRun, shouldSchedule, shouldContinueRunning" // into one result, e.g. selectedNode. var insufficientResourceErr error for _, r := range reasons { klog.V(4).Infof("DaemonSet Predicates failed on node %s for ds '%s/%s' for reason: %v", node.Name, ds.ObjectMeta.Namespace, ds.ObjectMeta.Name, r.GetReason()) switch reason := r.(type) { case *predicates.InsufficientResourceError: insufficientResourceErr = reason case *predicates.PredicateFailureError: var emitEvent bool // we try to partition predicates into two partitions here: intentional on the part of the operator and not. switch reason { // intentional case predicates.ErrNodeSelectorNotMatch, predicates.ErrPodNotMatchHostName, predicates.ErrNodeLabelPresenceViolated, // this one is probably intentional since it's a workaround for not having // pod hard anti affinity. predicates.ErrPodNotFitsHostPorts: return false, false, false, nil case predicates.ErrTaintsTolerationsNotMatch: // DaemonSet is expected to respect taints and tolerations fitsNoExecute, _, err := predicates.PodToleratesNodeNoExecuteTaints(newPod, nil, nodeInfo) if err != nil { return false, false, false, err } if !fitsNoExecute { return false, false, false, nil } wantToRun, shouldSchedule = false, false // unintentional case predicates.ErrDiskConflict, predicates.ErrVolumeZoneConflict, predicates.ErrMaxVolumeCountExceeded, predicates.ErrNodeUnderMemoryPressure, predicates.ErrNodeUnderDiskPressure: // wantToRun and shouldContinueRunning are likely true here. They are // absolutely true at the time of writing the comment. See first comment // of this method. shouldSchedule = false emitEvent = true // unexpected case predicates.ErrPodAffinityNotMatch, predicates.ErrServiceAffinityViolated: klog.Warningf("unexpected predicate failure reason: %s", reason.GetReason()) return false, false, false, fmt.Errorf("unexpected reason: DaemonSet Predicates should not return reason %s", reason.GetReason()) default: klog.V(4).Infof("unknown predicate failure reason: %s", reason.GetReason()) wantToRun, shouldSchedule, shouldContinueRunning = false, false, false emitEvent = true } if emitEvent { dsc.eventRecorder.Eventf(ds, v1.EventTypeWarning, FailedPlacementReason, "failed to place pod on %q: %s", node.ObjectMeta.Name, reason.GetReason()) } } } // only emit this event if insufficient resource is the only thing // preventing the daemon pod from scheduling if shouldSchedule && insufficientResourceErr != nil { dsc.eventRecorder.Eventf(ds, v1.EventTypeWarning, FailedPlacementReason, "failed to place pod on %q: %s", node.ObjectMeta.Name, insufficientResourceErr.Error()) shouldSchedule = false } return } 

• 如果shouldSchedule && !exists，则会把该Pod加入到nodesNeedingDaemonPods中。

• 如果shouldContinueRunning && pod.DeletionTimestamp == nil && pod.Status.Phase == v1.PodFailed则检查是否在流控周期（15min, hardcode）中，如果已经超过流控周期，会把该Pod加入到podsToDelete中，否则将再次入队列。

• 如果shouldContinueRunning && pod.DeletionTimestamp == nil && pod.Status.Phase != v1.PodFailed则会把该Pod加入到daemonPodsRunning中记录着该DamonSet在该Node上正在运行的非Failed的Pods，如果daemonPodsRunning不止一个，则需要按照创建时间排序，将不是最早创建的其他所有DaemonSet Pods都加入到podsToDelete中。

在nodeShouldRunDaemonPod中调用simulate仿真调度返回Pod和Node的匹配结果，根据algorithm.PredicateFailureReason结果知道wantToRun，shouldSchedule,shouldContinueRunning的值。下面我们看看simulate中的调度逻辑。

// Predicates checks if a DaemonSet's pod can be scheduled on a node using GeneralPredicates // and PodToleratesNodeTaints predicate func Predicates(pod *v1.Pod, nodeInfo *schedulercache.NodeInfo) (bool, []algorithm.PredicateFailureReason, error) { var predicateFails []algorithm.PredicateFailureReason // If ScheduleDaemonSetPods is enabled, only check nodeSelector, nodeAffinity and toleration/taint match. if utilfeature.DefaultFeatureGate.Enabled(features.ScheduleDaemonSetPods) { fit, reasons, err := checkNodeFitness(pod, nil, nodeInfo) if err != nil { return false, predicateFails, err } if !fit { predicateFails = append(predicateFails, reasons...) } return len(predicateFails) == 0, predicateFails, nil } critical := kubelettypes.IsCriticalPod(pod) fit, reasons, err := predicates.PodToleratesNodeTaints(pod, nil, nodeInfo) if err != nil { return false, predicateFails, err } if !fit { predicateFails = append(predicateFails, reasons...) } if critical { // If the pod is marked as critical and support for critical pod annotations is enabled, // check predicates for critical pods only. fit, reasons, err = predicates.EssentialPredicates(pod, nil, nodeInfo) } else { fit, reasons, err = predicates.GeneralPredicates(pod, nil, nodeInfo) } if err != nil { return false, predicateFails, err } if !fit { predicateFails = append(predicateFails, reasons...) } return len(predicateFails) == 0, predicateFails, nil } 

• 如果是启用了ScheduleDaemonSetPods FeatureGate，则Predicate逻辑如下。这里并没有真正的完成调度，只是做了三个predicate检查，最终的调度还是会交给default scheduler。default scheduler又是如何控制DaemonSet Pod和Node绑定关系的呢，先买个关子。
  • PodFitsHost: 检查Pod.spec.nodeName非空时是否与Node Name匹配；
  • PodMatchNodeSelector: 检查Pod的NodeSelector和NodeAffinity是否与Node匹配；
  • PodToleratesNodeTaints: 检查Pod的NoExecute和NoSchedule类型的Toleration是否与Node Taint匹配。
• 如果是没启用ScheduleDaemonSetPods FeatureGate，则Predicate逻辑如下。这里并没有真正的完成调度，只是做了几个predicate检查，最终的调度还是会交给DaemonSet Controller。
  • PodToleratesNodeTaints：检查Pod的NoExecute和NoSchedule类型的Toleration是否与Node Taint匹配。
  • 如果是Critical DaemonSet Pod，则再进行EssentialPredicates，包括：
    • PodFitsHost：检查Pod.spec.nodeName非空时是否与Node Name匹配；
    • PodFitsHostPorts：检查DaemonSet Pods请求的协议&Host端口是否已经被占用；
    • PodMatchNodeSelector: 检查Pod的NodeSelector和NodeAffinity是否与Node匹配；
  • 如果不是Critical DaemonSet Pod，则再进行GeneralPredicates，
    • PodFitsResources:检查Node剩余可分配资源是否能满足Pod请求；
    • PodFitsHost: 检查Pod.spec.nodeName非空时是否与Node Name匹配；
    • PodFitsHostPorts: 检查DaemonSet Pods请求的协议&Host端口是否已经被占用；
    • PodMatchNodeSelector: 检查Pod的NodeSelector和NodeAffinity是否与Node匹配；

Sync Nodes

前面通过podsShouldBeOnNode得到了nodesNeedingDaemonPods []string, podsToDelete []string, failedPodsObserved int，接下来就该去创建和删除对应的Pods了。

// syncNodes deletes given pods and creates new daemon set pods on the given nodes // returns slice with erros if any func (dsc *DaemonSetsController) syncNodes(ds *apps.DaemonSet, podsToDelete, nodesNeedingDaemonPods []string, hash string) error { // We need to set expectations before creating/deleting pods to avoid race conditions. dsKey, err := controller.KeyFunc(ds) if err != nil { return fmt.Errorf("couldn't get key for object %#v: %v", ds, err) } createDiff := len(nodesNeedingDaemonPods) deleteDiff := len(podsToDelete) if createDiff > dsc.burstReplicas { createDiff = dsc.burstReplicas } if deleteDiff > dsc.burstReplicas { deleteDiff = dsc.burstReplicas } dsc.expectations.SetExpectations(dsKey, createDiff, deleteDiff) // error channel to communicate back failures. make the buffer big enough to avoid any blocking errCh := make(chan error, createDiff+deleteDiff) klog.V(4).Infof("Nodes needing daemon pods for daemon set %s: %+v, creating %d", ds.Name, nodesNeedingDaemonPods, createDiff) createWait := sync.WaitGroup{} // If the returned error is not nil we have a parse error. // The controller handles this via the hash. generation, err := util.GetTemplateGeneration(ds) if err != nil { generation = nil } template := util.CreatePodTemplate(ds.Namespace, ds.Spec.Template, generation, hash) // Batch the pod creates. Batch sizes start at SlowStartInitialBatchSize // and double with each successful iteration in a kind of "slow start". // This handles attempts to start large numbers of pods that would // likely all fail with the same error. For example a project with a // low quota that attempts to create a large number of pods will be // prevented from spamming the API service with the pod create requests // after one of its pods fails. Conveniently, this also prevents the // event spam that those failures would generate. batchSize := integer.IntMin(createDiff, controller.SlowStartInitialBatchSize) for pos := 0; createDiff > pos; batchSize, pos = integer.IntMin(2*batchSize, createDiff-(pos+batchSize)), pos+batchSize { errorCount := len(errCh) createWait.Add(batchSize) for i := pos; i < pos+batchSize; i++ { go func(ix int) { defer createWait.Done() var err error podTemplate := &template if utilfeature.DefaultFeatureGate.Enabled(features.ScheduleDaemonSetPods) { podTemplate = template.DeepCopy() // The pod's NodeAffinity will be updated to make sure the Pod is bound // to the target node by default scheduler. It is safe to do so because there // should be no conflicting node affinity with the target node. podTemplate.Spec.Affinity = util.ReplaceDaemonSetPodNodeNameNodeAffinity( podTemplate.Spec.Affinity, nodesNeedingDaemonPods[ix]) err = dsc.podControl.CreatePodsWithControllerRef(ds.Namespace, podTemplate, ds, metav1.NewControllerRef(ds, controllerKind)) } else { err = dsc.podControl.CreatePodsOnNode(nodesNeedingDaemonPods[ix], ds.Namespace, podTemplate, ds, metav1.NewControllerRef(ds, controllerKind)) } if err != nil && errors.IsTimeout(err) { // Pod is created but its initialization has timed out. // If the initialization is successful eventually, the // controller will observe the creation via the informer. // If the initialization fails, or if the pod keeps // uninitialized for a long time, the informer will not // receive any update, and the controller will create a new // pod when the expectation expires. return } if err != nil { klog.V(2).Infof("Failed creation, decrementing expectations for set %q/%q", ds.Namespace, ds.Name) dsc.expectations.CreationObserved(dsKey) errCh <- err utilruntime.HandleError(err) } }(i) } createWait.Wait() // any skipped pods that we never attempted to start shouldn't be expected. skippedPods := createDiff - batchSize if errorCount < len(errCh) && skippedPods > 0 { klog.V(2).Infof("Slow-start failure. Skipping creation of %d pods, decrementing expectations for set %q/%q", skippedPods, ds.Namespace, ds.Name) for i := 0; i < skippedPods; i++ { dsc.expectations.CreationObserved(dsKey) } // The skipped pods will be retried later. The next controller resync will // retry the slow start process. break } } klog.V(4).Infof("Pods to delete for daemon set %s: %+v, deleting %d", ds.Name, podsToDelete, deleteDiff) deleteWait := sync.WaitGroup{} deleteWait.Add(deleteDiff) for i := 0; i < deleteDiff; i++ { go func(ix int) { defer deleteWait.Done() if err := dsc.podControl.DeletePod(ds.Namespace, podsToDelete[ix], ds); err != nil { klog.V(2).Infof("Failed deletion, decrementing expectations for set %q/%q", ds.Namespace, ds.Name) dsc.expectations.DeletionObserved(dsKey) errCh <- err utilruntime.HandleError(err) } }(i) } deleteWait.Wait() // collect errors if any for proper reporting/retry logic in the controller errors := []error{} close(errCh) for err := range errCh { errors = append(errors, err) } return utilerrors.NewAggregate(errors) } 

• 每次删除和创建的最大Pods个数分别为250个。
• 根据DaemonSet Object构建Pod Template，并且增加/更新以下Tolerations：
  • node.kubernetes.io/not-ready | exist | NoExecute
  • node.kubernetes.io/unreachable | exist | NoExecute
  • node.kubernetes.io/disk-pressure | exist | NoSchedule
  • node.kubernetes.io/memory-pressure | exist | NoSchedule
  • node.kubernetes.io/unschedulable | exist | NoSchedule
  • node.kubernetes.io/network-unavailable | exist | NoSchedule
  • 如果是Critical Pod，还会增加以下Tolerations：
    • node.kubernetes.io/out-of-disk | exist | NoExecute
    • node.kubernetes.io/out-of-disk | exist | NoSchedule
• 给Pod加上Label: controller-revision-hash=$DaemonSetControlelrHash
• 分批的创建DaemonSet Pods（按照1,2,4,8,...的batch size去Create DaemonSet Pods，防止大批量的一次性创建所有DaemonSet Pods时因同样的错误导致失败。对于创建失败的Pods，注意更新expectations中的Adds值，每失败一个就会将expectations.adds值减1。
  • 如果启用了ScheduleDaemonSetPods FeatureGate，则往Pod Tempalete中添加/更新metadata.name=$NodeName的NodeAffinity。通过这种方式，来实现通过default scheduler来调度DaemonSet Pods的目的。
• 一次性的删除podsToDelete的Pods。

DaemonSet的滚动更新

DaemonSet的滚动更新，跟Deployment的滚动更新略有不同，DaemonSet RollingUpdate只有MaxUnavailable这一个配置项，没有MinAvailable。

// rollingUpdate deletes old daemon set pods making sure that no more than // ds.Spec.UpdateStrategy.RollingUpdate.MaxUnavailable pods are unavailable func (dsc *DaemonSetsController) rollingrollingrollingUpdate(ds *apps.DaemonSet, hash string) error { nodeToDaemonPods, err := dsc.getNodesToDaemonPods(ds) if err != nil { return fmt.Errorf("couldn't get node to daemon pod mapping for daemon set %q: %v", ds.Name, err) } _, oldPods := dsc.getAllDaemonSetPods(ds, nodeToDaemonPods, hash) maxUnavailable, numUnavailable, err := dsc.getUnavailableNumbers(ds, nodeToDaemonPods) if err != nil { return fmt.Errorf("Couldn't get unavailable numbers: %v", err) } oldAvailablePods, oldUnavailablePods := util.SplitByAvailablePods(ds.Spec.MinReadySeconds, oldPods) // for oldPods delete all not running pods var oldPodsToDelete []string klog.V(4).Infof("Marking all unavailable old pods for deletion") for _, pod := range oldUnavailablePods { // Skip terminating pods. We won't delete them again if pod.DeletionTimestamp != nil { continue } klog.V(4).Infof("Marking pod %s/%s for deletion", ds.Name, pod.Name) oldPodsToDelete = append(oldPodsToDelete, pod.Name) } klog.V(4).Infof("Marking old pods for deletion") for _, pod := range oldAvailablePods { if numUnavailable >= maxUnavailable { klog.V(4).Infof("Number of unavailable DaemonSet pods: %d, is equal to or exceeds allowed maximum: %d", numUnavailable, maxUnavailable) break } klog.V(4).Infof("Marking pod %s/%s for deletion", ds.Name, pod.Name) oldPodsToDelete = append(oldPodsToDelete, pod.Name) numUnavailable++ } return dsc.syncNodes(ds, oldPodsToDelete, []string{}, hash) } 

• 根据最新的Hash值选出所有的OldPods；
• 计算那些!available及那些期望调度但还没运行的Pods之和，作为numUnavailable。
• 将OldPods分为oldAvailablePods和oldUnavailablePods，将DeletionTimestamp为空的oldUnavailablePods加入到待删除Pods列表（oldPodsToDelete）。
• 遍历oldAvailablePods，逐个加入到oldPodsToDelete中，直到numUnavailable达到maxUnavailable为止，从oldAvailablePods加入到oldPodsToDelete的Pods最大个数为(maxUnavailable - 1)。
• 因此，oldPodsToDelete包括所有的DeletionTimestamp为空的oldUnavailablePods及最多(maxUnavailable - 1)个oldAvailablePods。
• 最后调用syncNodes开始删除oldPodsToDelete中的DaemonSet Pods。

Node更新

Node Add事件很简单，遍历所有DaemonSets对象，调用nodeShouldRunDaemonPod计算出每个DaemonSet是否应该在该Node上启动。如果要启动，则把DaemonSet加入到Queue，由syncDaemonSet进行处理。

对于Node Update事件，需要判断Update的字段等，然后根据情况决定是否要加入到Queue进行syncDaemonSet。

func (dsc *DaemonSetsController) updateNode(old, cur interface{}) { oldNode := old.(*v1.Node) curNode := cur.(*v1.Node) if shouldIgnoreNodeUpdate(*oldNode, *curNode) { return } dsList, err := dsc.dsLister.List(labels.Everything()) if err != nil { klog.V(4).Infof("Error listing daemon sets: %v", err) return } // TODO: it'd be nice to pass a hint with these enqueues, so that each ds would only examine the added node (unless it has other work to do, too). for _, ds := range dsList { _, oldShouldSchedule, oldShouldContinueRunning, err := dsc.nodeShouldRunDaemonPod(oldNode, ds) if err != nil { continue } _, currentShouldSchedule, currentShouldContinueRunning, err := dsc.nodeShouldRunDaemonPod(curNode, ds) if err != nil { continue } if (oldShouldSchedule != currentShouldSchedule) || (oldShouldContinueRunning != currentShouldContinueRunning) { dsc.enqueueDaemonSet(ds) } } } 

• 如果Node Condition没有发生变更，则不能忽略该Node变更事件。
• 除了Node Condition和ResourceVersion之外，如果新旧Node对象不一致，也不能忽略该变更事件。
• 对于不能忽略的变更，则分别对于oldNode，currentNode调用nodeShouldRunDaemonPod计算ShouldSchedule、ShouldContinueRunning是否一致，只要ShouldSchedule或者ShouldContinueRunning发生变更，则将该DaemonSet Object入队列进入syncDaemonSet进行处理。

DaemonSet Controller主体逻辑

总结

本文主要对DaemonSet的结构、创建、同步、调度、滚动更新几个方面进行了源码分析，在生产环境中使用DaemonSet进行大规模部署使用之前，加深这些了解是有帮助的。下一篇博客，我将会从一些实际问题出发，从用户角度分析DaemonSet的若干行为。比如，Node Taint变更后DaemonSet的行为、DaemonSet删除时异常导致Hang住的原因及解决办法、Node NotReady时DamonSet Pods会怎么样等思考。