Daemonset Controller对Critical Pod的特殊处理是什么

这篇文章主要介绍"Daemonset Controller对Critical Pod的特殊处理是什么"，在日常操作中，相信很多人在Daemonset Controller对Critical Pod的特殊处理是什么问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答"Daemonset Controller对Critical Pod的特殊处理是什么"的疑惑有所帮助！接下来，请跟着小编一起来学习吧！

Daemonset Controller对CriticalPod的特殊处理

在DaemonSetController判断某个node上是否要运行某个DaemonSet时，会调用DaemonSetsController.simulate来分析PredicateFailureReason。

pkg/controller/daemon/daemon_controller.go:1206func (dsc *DaemonSetsController) simulate(newPod *v1.Pod, node *v1.Node, ds *apps.DaemonSet) ([]algorithm.PredicateFailureReason, *schedulercache.NodeInfo, error) {        // DaemonSet pods shouldn't be deleted by NodeController in case of node problems.        // Add infinite toleration for taint notReady:NoExecute here        // to survive taint-based eviction enforced by NodeController        // when node turns not ready.        v1helper.AddOrUpdateTolerationInPod(newPod, &v1.Toleration{                Key:      algorithm.TaintNodeNotReady,                Operator: v1.TolerationOpExists,                Effect:   v1.TaintEffectNoExecute,        })        // DaemonSet pods shouldn't be deleted by NodeController in case of node problems.        // Add infinite toleration for taint unreachable:NoExecute here        // to survive taint-based eviction enforced by NodeController        // when node turns unreachable.        v1helper.AddOrUpdateTolerationInPod(newPod, &v1.Toleration{                Key:      algorithm.TaintNodeUnreachable,                Operator: v1.TolerationOpExists,                Effect:   v1.TaintEffectNoExecute,        })        // According to TaintNodesByCondition, all DaemonSet pods should tolerate        // MemoryPressure and DisPressure taints, and the critical pods should tolerate        // OutOfDisk taint additional.        v1helper.AddOrUpdateTolerationInPod(newPod, &v1.Toleration{                Key:      algorithm.TaintNodeDiskPressure,                Operator: v1.TolerationOpExists,                Effect:   v1.TaintEffectNoSchedule,        })        v1helper.AddOrUpdateTolerationInPod(newPod, &v1.Toleration{                Key:      algorithm.TaintNodeMemoryPressure,                Operator: v1.TolerationOpExists,                Effect:   v1.TaintEffectNoSchedule,        })        // TODO(#48843) OutOfDisk taints will be removed in 1.10        if utilfeature.DefaultFeatureGate.Enabled(features.ExperimentalCriticalPodAnnotation) &&                kubelettypes.IsCriticalPod(newPod) {                v1helper.AddOrUpdateTolerationInPod(newPod, &v1.Toleration{                        Key:      algorithm.TaintNodeOutOfDisk,                        Operator: v1.TolerationOpExists,                        Effect:   v1.TaintEffectNoSchedule,                })        }        ...        _, reasons, err := Predicates(newPod, nodeInfo)        return reasons, nodeInfo, err}

• DeamonSetController会给Pod添加以下Toleratoins，防止Node出现以下Conditions被Node Controller Taint-based eviction杀死。

• NotReady:NoExecute

• Unreachable:NoExecute

• MemoryPressure:NoSchedule

• DisPressure:NoSchedule

• 当ExperimentalCriticalPodAnnotation Feature Gate Enable，并且该Pod是CriticalPod时，还会给该Pod加上OutOfDisk:NoSchedule Toleration。

在simulate中，还会像类似scheduler一样，进行Predicates处理。Predicates过程中也对CriticalPod做了区分对待。

pkg/controller/daemon/daemon_controller.go:1413// Predicates checks if a DaemonSet's pod can be scheduled on a node using GeneralPredicates// and PodToleratesNodeTaints predicatefunc Predicates(pod *v1.Pod, nodeInfo *schedulercache.NodeInfo) (bool, []algorithm.PredicateFailureReason, error) {        var predicateFails []algorithm.PredicateFailureReason        // If ScheduleDaemonSetPods is enabled, only check nodeSelector and nodeAffinity.        if false /*disabled for 1.10*/ && utilfeature.DefaultFeatureGate.Enabled(features.ScheduleDaemonSetPods) {                fit, reasons, err := nodeSelectionPredicates(pod, nil, nodeInfo)                if err != nil {                        return false, predicateFails, err                }                if !fit {                        predicateFails = append(predicateFails, reasons...)                }                return len(predicateFails) == 0, predicateFails, nil        }        critical := utilfeature.DefaultFeatureGate.Enabled(features.ExperimentalCriticalPodAnnotation) &&                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CriticalPod，调用predicates.EssentialPredicates，否则调用predicates.GeneralPredicates。

• 这里的GeneralPredicates与EssentialPredicates有何不同呢？其实GeneralPredicates就是比EssentialPredicates多了noncriticalPredicates处理，也就是Scheduler的Predicate中的PodFitsResources。

pkg/scheduler/algorithm/predicates/predicates.go:1076// noncriticalPredicates are the predicates that only non-critical pods needfunc noncriticalPredicates(pod *v1.Pod, meta algorithm.PredicateMetadata, nodeInfo *schedulercache.NodeInfo) (bool, []algorithm.PredicateFailureReason, error) {        var predicateFails []algorithm.PredicateFailureReason        fit, reasons, err := PodFitsResources(pod, meta, nodeInfo)        if err != nil {                return false, predicateFails, err        }        if !fit {                predicateFails = append(predicateFails, reasons...)        }        return len(predicateFails) == 0, predicateFails, nil}

因此，对于CriticalPod，DeamonSetController进行Predicate时不会进行PodFitsResources检查。

PriorityClass Validate对CriticalPod的特殊处理

在Kubernetes 1.11中，很重要的个更新就是，Priority和Preemption从alpha升级为Beta了，并且是Enabled by default。

PriorityClass是属于scheduling.k8s.io/v1alpha1GroupVersion的，在client提交创建PriorityClass请求后，写入etcd前，会进行合法性检查（Validate），这其中就有对SystemClusterCritical和SystemNodeCritical两个PriorityClass的特殊对待。

pkg/apis/scheduling/validation/validation.go:30// ValidatePriorityClass tests whether required fields in the PriorityClass are// set correctly.func ValidatePriorityClass(pc *scheduling.PriorityClass) field.ErrorList {        ...        // If the priorityClass starts with a system prefix, it must be one of the        // predefined system priority classes.        if strings.HasPrefix(pc.Name, scheduling.SystemPriorityClassPrefix) {                if is, err := scheduling.IsKnownSystemPriorityClass(pc); !is {                        allErrs = append(allErrs, field.Forbidden(field.NewPath("metadata", "name"), "priority class names with '"+scheduling.SystemPriorityClassPrefix+"' prefix are reserved for system use only. error: "+err.Error()))                }        }         ...        return allErrs}// IsKnownSystemPriorityClass checks that "pc" is equal to one of the system PriorityClasses.// It ignores "description", labels, annotations, etc. of the PriorityClass.func IsKnownSystemPriorityClass(pc *PriorityClass) (bool, error) {        for _, spc := range systemPriorityClasses {                if spc.Name == pc.Name {                        if spc.Value != pc.Value {                                return false, fmt.Errorf("value of %v PriorityClass must be %v", spc.Name, spc.Value)                        }                        if spc.GlobalDefault != pc.GlobalDefault {                                return false, fmt.Errorf("globalDefault of %v PriorityClass must be %v", spc.Name, spc.GlobalDefault)                        }                        return true, nil                }        }        return false, fmt.Errorf("%v is not a known system priority class", pc.Name)}

• PriorityClass的Validate时，如果PriorityClass's Name是以**system-**为前缀的，那么必须是system-cluster-critical或者system-node-critical之一。否则就会Validate Error，拒绝提交。

• 如果提交的PriorityClass's Name为system-cluster-critical或者system-node-critical，那么要求globalDefault必须为false，即system-cluster-critical或者system-node-critical不能是全局默认的PriorityClass。

另外，在PriorityClass进行Update时，目前是不允许其Name和Value的，也就是说只能更新Description和globalDefault。

pkg/apis/scheduling/helpers.go:27// SystemPriorityClasses define system priority classes that are auto-created at cluster bootstrapping.// Our API validation logic ensures that any priority class that has a system prefix or its value// is higher than HighestUserDefinablePriority is equal to one of these SystemPriorityClasses.var systemPriorityClasses = []*PriorityClass{        {                ObjectMeta: metav1.ObjectMeta{                        Name: SystemNodeCritical,                },                Value:       SystemCriticalPriority + 1000,                Description: "Used for system critical pods that must not be moved from their current node.",        },        {                ObjectMeta: metav1.ObjectMeta{                        Name: SystemClusterCritical,                },                Value:       SystemCriticalPriority,                Description: "Used for system critical pods that must run in the cluster, but can be moved to another node if necessary.",        },}

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