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摘要：本文分析了DeamonSetController及PriorityClass Validate时，对CriticalPod的所做的特殊处理。
深入分析Kubernetes Critical Pod系列：
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。
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} 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。
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。
| Kubernetes Version | Priority and Preemption State | Enabled by default |
|---|---|---|
| 1.8 | alpha | no |
| 1.9 | alpha | no |
| 1.10 | alpha | no |
| 1.11 | beta | yes |
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)} system-cluster-critical或者system-node-critical之一。否则就会Validate Error，拒绝提交。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.", },} 因此DeamonSetController及PriorityClass Validate时，对CriticalPod的特殊处理总结如下：
OutOfDisk:NoScheduleToleration。system-cluster-critical或者system-node-critical之一。否则就会Validate Error，拒绝提交。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。转载地址：http://ghhbl.baihongyu.com/