Kube Scheduler 源码分析
Kube Scheduler 是负责k8s 集群最终Pod 应该部署到哪台机器的决策者，本章来走读一下Scheduler 基本流程源码。
func NewSchedulerCommand() *cobra.Command {
opts, err := options.NewOptions()
if err != nil {
klog.Fatalf("unable to initialize command options: %v", err)
}
cmd := &cobra.Command{
Use: "kube-scheduler",
Long: `The Kubernetes scheduler is a policy-rich, topology-aware,
workload-specific function that significantly impacts availability, performance,
and capacity. The scheduler needs to take into account individual and collective
resource requirements, quality of service requirements, hardware/software/policy
constraints, affinity and anti-affinity specifications, data locality, inter-workload
interference, deadlines, and so on. Workload-specific requirements will be exposed
through the API as necessary.`,
Run: func(cmd *cobra.Command, args []string) {
if err := runCommand(cmd, args, opts); err != nil {
fmt.Fprintf(os.Stderr, "%v\n", err)
os.Exit(1)
}
},
}Scheduler 也是一个command line ，启动参数和另外几个组件无异。
Scheduler Run 函数
// Run executes the scheduler based on the given configuration. It only return on error or when stopCh is closed.
func Run(cc schedulerserverconfig.CompletedConfig, stopCh <-chan struct{}) error {
// Create the scheduler.
sched, err := scheduler.New(cc.Client,
cc.InformerFactory.Core().V1().Nodes(),
cc.PodInformer,
cc.InformerFactory.Core().V1().PersistentVolumes(),
cc.InformerFactory.Core().V1().PersistentVolumeClaims(),
cc.InformerFactory.Core().V1().ReplicationControllers(),
cc.InformerFactory.Apps().V1().ReplicaSets(),
cc.InformerFactory.Apps().V1().StatefulSets(),
cc.InformerFactory.Core().V1().Services(),
cc.InformerFactory.Policy().V1beta1().PodDisruptionBudgets(),
cc.InformerFactory.Storage().V1().StorageClasses(),
cc.Recorder,
cc.ComponentConfig.AlgorithmSource,
stopCh,
scheduler.WithName(cc.ComponentConfig.SchedulerName),
scheduler.WithHardPodAffinitySymmetricWeight(cc.ComponentConfig.HardPodAffinitySymmetricWeight),
scheduler.WithPreemptionDisabled(cc.ComponentConfig.DisablePreemption),
scheduler.WithPercentageOfNodesToScore(cc.ComponentConfig.PercentageOfNodesToScore),
scheduler.WithBindTimeoutSeconds(*cc.ComponentConfig.BindTimeoutSeconds))
if err != nil {
return err
}
// Start all informers.
go cc.PodInformer.Informer().Run(stopCh)
cc.InformerFactory.Start(stopCh)
// Wait for all caches to sync before scheduling.
cc.InformerFactory.WaitForCacheSync(stopCh)
controller.WaitForCacheSync("scheduler", stopCh, cc.PodInformer.Informer().HasSynced)
// Prepare a reusable runCommand function.
run := func(ctx context.Context) {
sched.Run()
<-ctx.Done()
}
ctx, cancel := context.WithCancel(context.TODO()) // TODO once Run() accepts a context, it should be used here
defer cancel()
go func() {
select {
case <-stopCh:
cancel()
case <-ctx.Done():
}
}()
// If leader election is enabled, runCommand via LeaderElector until done and exit.
if cc.LeaderElection != nil {
cc.LeaderElection.Callbacks = leaderelection.LeaderCallbacks{
OnStartedLeading: run,
OnStoppedLeading: func() {
utilruntime.HandleError(fmt.Errorf("lost master"))
},
}
leaderElector, err := leaderelection.NewLeaderElector(*cc.LeaderElection)
if err != nil {
return fmt.Errorf("couldn't create leader elector: %v", err)
}
leaderElector.Run(ctx)
return fmt.Errorf("lost lease")
}
// Leader election is disabled, so runCommand inline until done.
run(ctx)
return fmt.Errorf("finished without leader elect")
}可以看到Run 函数主要做如下几个流程
- 根据需要观察的Informer 创建Scheduler 实例
- 将所有的Informer Listener 运行起来
- 使用Client-go 进行选主
- 运行真正的调度 run 函数
scheduler.New 函数
// New returns a Scheduler
func New(client clientset.Interface,
nodeInformer coreinformers.NodeInformer,
podInformer coreinformers.PodInformer,
pvInformer coreinformers.PersistentVolumeInformer,
pvcInformer coreinformers.PersistentVolumeClaimInformer,
replicationControllerInformer coreinformers.ReplicationControllerInformer,
replicaSetInformer appsinformers.ReplicaSetInformer,
statefulSetInformer appsinformers.StatefulSetInformer,
serviceInformer coreinformers.ServiceInformer,
pdbInformer policyinformers.PodDisruptionBudgetInformer,
storageClassInformer storageinformers.StorageClassInformer,
recorder record.EventRecorder,
schedulerAlgorithmSource kubeschedulerconfig.SchedulerAlgorithmSource,
stopCh <-chan struct{},
opts ...func(o *schedulerOptions)) (*Scheduler, error) {
options := defaultSchedulerOptions
for _, opt := range opts {
opt(&options)
}
// Set up the configurator which can create schedulers from configs.
configurator := factory.NewConfigFactory(&factory.ConfigFactoryArgs{
SchedulerName: options.schedulerName,
Client: client,
NodeInformer: nodeInformer,
PodInformer: podInformer,
PvInformer: pvInformer,
PvcInformer: pvcInformer,
ReplicationControllerInformer: replicationControllerInformer,
ReplicaSetInformer: replicaSetInformer,
StatefulSetInformer: statefulSetInformer,
ServiceInformer: serviceInformer,
PdbInformer: pdbInformer,
StorageClassInformer: storageClassInformer,
HardPodAffinitySymmetricWeight: options.hardPodAffinitySymmetricWeight,
DisablePreemption: options.disablePreemption,
PercentageOfNodesToScore: options.percentageOfNodesToScore,
BindTimeoutSeconds: options.bindTimeoutSeconds,
})
var config *factory.Config
source := schedulerAlgorithmSource
switch {
case source.Provider != nil:
// Create the config from a named algorithm provider.
sc, err := configurator.CreateFromProvider(*source.Provider)
if err != nil {
return nil, fmt.Errorf("couldn't create scheduler using provider %q: %v", *source.Provider, err)
}
config = sc
case source.Policy != nil:
// Create the config from a user specified policy source.
policy := &schedulerapi.Policy{}
switch {
case source.Policy.File != nil:
if err := initPolicyFromFile(source.Policy.File.Path, policy); err != nil {
return nil, err
}
case source.Policy.ConfigMap != nil:
if err := initPolicyFromConfigMap(client, source.Policy.ConfigMap, policy); err != nil {
return nil, err
}
}
sc, err := configurator.CreateFromConfig(*policy)
if err != nil {
return nil, fmt.Errorf("couldn't create scheduler from policy: %v", err)
}
config = sc
default:
return nil, fmt.Errorf("unsupported algorithm source: %v", source)
}
// Additional tweaks to the config produced by the configurator.
config.Recorder = recorder
config.DisablePreemption = options.disablePreemption
config.StopEverything = stopCh
// Create the scheduler.
sched := NewFromConfig(config)
return sched, nil
}- 将所有的Informer 构建为一个Config Struct
- 根据Provider 或者 ConfigMap 来创建对应的调度器以及初始化策略(这里可以选择使用config file 或者configMap 模式来指定各种调度策略顺序和权重以及是否开启)
- 将返回的config 构建成对应的schedu 实例返回
CreateFromConfig
这里我们以Policy 为例看一下具体如何根据config file 创建对应的Scheduler Struct。
// Creates a scheduler from the configuration file
func (c *configFactory) CreateFromConfig(policy schedulerapi.Policy) (*Config, error) {
klog.V(2).Infof("Creating scheduler from configuration: %v", policy)
// validate the policy configuration
if err := validation.ValidatePolicy(policy); err != nil {
return nil, err
}
predicateKeys := sets.NewString()
if policy.Predicates == nil {
klog.V(2).Infof("Using predicates from algorithm provider '%v'", DefaultProvider)
provider, err := GetAlgorithmProvider(DefaultProvider)
if err != nil {
return nil, err
}
predicateKeys = provider.FitPredicateKeys
} else {
for _, predicate := range policy.Predicates {
klog.V(2).Infof("Registering predicate: %s", predicate.Name)
predicateKeys.Insert(RegisterCustomFitPredicate(predicate))
}
}
priorityKeys := sets.NewString()
if policy.Priorities == nil {
klog.V(2).Infof("Using priorities from algorithm provider '%v'", DefaultProvider)
provider, err := GetAlgorithmProvider(DefaultProvider)
if err != nil {
return nil, err
}
priorityKeys = provider.PriorityFunctionKeys
} else {
for _, priority := range policy.Priorities {
klog.V(2).Infof("Registering priority: %s", priority.Name)
priorityKeys.Insert(RegisterCustomPriorityFunction(priority))
}
}
var extenders []algorithm.SchedulerExtender
if len(policy.ExtenderConfigs) != 0 {
ignoredExtendedResources := sets.NewString()
for ii := range policy.ExtenderConfigs {
klog.V(2).Infof("Creating extender with config %+v", policy.ExtenderConfigs[ii])
extender, err := core.NewHTTPExtender(&policy.ExtenderConfigs[ii])
if err != nil {
return nil, err
}
extenders = append(extenders, extender)
for _, r := range policy.ExtenderConfigs[ii].ManagedResources {
if r.IgnoredByScheduler {
ignoredExtendedResources.Insert(string(r.Name))
}
}
}
predicates.RegisterPredicateMetadataProducerWithExtendedResourceOptions(ignoredExtendedResources)
}- 如果没有设置
Predicates则初始化default Predicates - 如果没有设置
Priorities则初始化default Priorities - 如果设置
ExtenderConfigs则初始化ExtenderConfigs
下面列一下都有哪些Predicates
// MatchInterPodAffinityPred defines the name of predicate MatchInterPodAffinity.
MatchInterPodAffinityPred = "MatchInterPodAffinity"
// CheckVolumeBindingPred defines the name of predicate CheckVolumeBinding.
CheckVolumeBindingPred = "CheckVolumeBinding"
// CheckNodeConditionPred defines the name of predicate CheckNodeCondition.
CheckNodeConditionPred = "CheckNodeCondition"
// GeneralPred defines the name of predicate GeneralPredicates.
GeneralPred = "GeneralPredicates"
// HostNamePred defines the name of predicate HostName.
HostNamePred = "HostName"
// PodFitsHostPortsPred defines the name of predicate PodFitsHostPorts.
PodFitsHostPortsPred = "PodFitsHostPorts"
// MatchNodeSelectorPred defines the name of predicate MatchNodeSelector.
MatchNodeSelectorPred = "MatchNodeSelector"
// PodFitsResourcesPred defines the name of predicate PodFitsResources.
PodFitsResourcesPred = "PodFitsResources"
// NoDiskConflictPred defines the name of predicate NoDiskConflict.
NoDiskConflictPred = "NoDiskConflict"
// PodToleratesNodeTaintsPred defines the name of predicate PodToleratesNodeTaints.
PodToleratesNodeTaintsPred = "PodToleratesNodeTaints"
// CheckNodeUnschedulablePred defines the name of predicate CheckNodeUnschedulablePredicate.
CheckNodeUnschedulablePred = "CheckNodeUnschedulable"
// PodToleratesNodeNoExecuteTaintsPred defines the name of predicate PodToleratesNodeNoExecuteTaints.
PodToleratesNodeNoExecuteTaintsPred = "PodToleratesNodeNoExecuteTaints"
// CheckNodeLabelPresencePred defines the name of predicate CheckNodeLabelPresence.
CheckNodeLabelPresencePred = "CheckNodeLabelPresence"
// CheckServiceAffinityPred defines the name of predicate checkServiceAffinity.
CheckServiceAffinityPred = "CheckServiceAffinity"
// MaxEBSVolumeCountPred defines the name of predicate MaxEBSVolumeCount.
MaxEBSVolumeCountPred = "MaxEBSVolumeCount"
// MaxGCEPDVolumeCountPred defines the name of predicate MaxGCEPDVolumeCount.
MaxGCEPDVolumeCountPred = "MaxGCEPDVolumeCount"
// MaxAzureDiskVolumeCountPred defines the name of predicate MaxAzureDiskVolumeCount.
MaxAzureDiskVolumeCountPred = "MaxAzureDiskVolumeCount"
// MaxCinderVolumeCountPred defines the name of predicate MaxCinderDiskVolumeCount.
MaxCinderVolumeCountPred = "MaxCinderVolumeCount"
// MaxCSIVolumeCountPred defines the predicate that decides how many CSI volumes should be attached
MaxCSIVolumeCountPred = "MaxCSIVolumeCountPred"
// NoVolumeZoneConflictPred defines the name of predicate NoVolumeZoneConflict.
NoVolumeZoneConflictPred = "NoVolumeZoneConflict"
// CheckNodeMemoryPressurePred defines the name of predicate CheckNodeMemoryPressure.
CheckNodeMemoryPressurePred = "CheckNodeMemoryPressure"
// CheckNodeDiskPressurePred defines the name of predicate CheckNodeDiskPressure.
CheckNodeDiskPressurePred = "CheckNodeDiskPressure"
// CheckNodePIDPressurePred defines the name of predicate CheckNodePIDPressure.
CheckNodePIDPressurePred = "CheckNodePIDPressure"
// DefaultMaxGCEPDVolumes defines the maximum number of PD Volumes for GCE
// GCE instances can have up to 16 PD volumes attached.
DefaultMaxGCEPDVolumes = 16
// DefaultMaxAzureDiskVolumes defines the maximum number of PD Volumes for Azure
// Larger Azure VMs can actually have much more disks attached.
// TODO We should determine the max based on VM size
DefaultMaxAzureDiskVolumes = 16
// KubeMaxPDVols defines the maximum number of PD Volumes per kubelet
KubeMaxPDVols = "KUBE_MAX_PD_VOLS"
// EBSVolumeFilterType defines the filter name for EBSVolumeFilter.
EBSVolumeFilterType = "EBS"
// GCEPDVolumeFilterType defines the filter name for GCEPDVolumeFilter.
GCEPDVolumeFilterType = "GCE"
// AzureDiskVolumeFilterType defines the filter name for AzureDiskVolumeFilter.
AzureDiskVolumeFilterType = "AzureDisk"
// CinderVolumeFilterType defines the filter name for CinderVolumeFilter.
CinderVolumeFilterType = "Cinder"所有的priorities如下
EqualPriority = "EqualPriority"
// MostRequestedPriority defines the name of prioritizer function that gives used nodes higher priority.
MostRequestedPriority = "MostRequestedPriority"
// RequestedToCapacityRatioPriority defines the name of RequestedToCapacityRatioPriority.
RequestedToCapacityRatioPriority = "RequestedToCapacityRatioPriority"
// SelectorSpreadPriority defines the name of prioritizer function that spreads pods by minimizing
// the number of pods (belonging to the same service or replication controller) on the same node.
SelectorSpreadPriority = "SelectorSpreadPriority"
// ServiceSpreadingPriority is largely replaced by "SelectorSpreadPriority".
ServiceSpreadingPriority = "ServiceSpreadingPriority"
// InterPodAffinityPriority defines the name of prioritizer function that decides which pods should or
// should not be placed in the same topological domain as some other pods.
InterPodAffinityPriority = "InterPodAffinityPriority"
// LeastRequestedPriority defines the name of prioritizer function that prioritize nodes by least
// requested utilization.
LeastRequestedPriority = "LeastRequestedPriority"
// BalancedResourceAllocation defines the name of prioritizer function that prioritizes nodes
// to help achieve balanced resource usage.
BalancedResourceAllocation = "BalancedResourceAllocation"
// NodePreferAvoidPodsPriority defines the name of prioritizer function that priorities nodes according to
// the node annotation "scheduler.alpha.kubernetes.io/preferAvoidPods".
NodePreferAvoidPodsPriority = "NodePreferAvoidPodsPriority"
// NodeAffinityPriority defines the name of prioritizer function that prioritizes nodes which have labels
// matching NodeAffinity.
NodeAffinityPriority = "NodeAffinityPriority"
// TaintTolerationPriority defines the name of prioritizer function that prioritizes nodes that marked
// with taint which pod can tolerate.
TaintTolerationPriority = "TaintTolerationPriority"
// ImageLocalityPriority defines the name of prioritizer function that prioritizes nodes that have images
// requested by the pod present.
ImageLocalityPriority = "ImageLocalityPriority"
// ResourceLimitsPriority defines the nodes of prioritizer function ResourceLimitsPriority.
ResourceLimitsPriority = "ResourceLimitsPriority"scheduleOne
// scheduleOne does the entire scheduling workflow for a single pod. It is serialized on the scheduling algorithm's host fitting.
func (sched *Scheduler) scheduleOne() {
plugins := sched.config.PluginSet
// Remove all plugin context data at the beginning of a scheduling cycle.
if plugins.Data().Ctx != nil {
plugins.Data().Ctx.Reset()
}
pod := sched.config.NextPod()
// pod could be nil when schedulerQueue is closed
if pod == nil {
return
}
if pod.DeletionTimestamp != nil {
sched.config.Recorder.Eventf(pod, v1.EventTypeWarning, "FailedScheduling", "skip schedule deleting pod: %v/%v", pod.Namespace, pod.Name)
klog.V(3).Infof("Skip schedule deleting pod: %v/%v", pod.Namespace, pod.Name)
return
}
klog.V(3).Infof("Attempting to schedule pod: %v/%v", pod.Namespace, pod.Name)
// Synchronously attempt to find a fit for the pod.
start := time.Now()
scheduleResult, err := sched.schedule(pod)
err := sched.bind(assumedPod, &v1.Binding{
ObjectMeta: metav1.ObjectMeta{Namespace: assumedPod.Namespace, Name: assumedPod.Name, UID: assumedPod.UID},
Target: v1.ObjectReference{
Kind: "Node",
Name: scheduleResult.SuggestedHost,
},
})这里就是最终调度Pod的最终函数，可以看到，它先从队列里面得到所有的未调度的 Pod，这里判断是否未调度主要根据Pod 的NodeName 是否已经被分配为标准，后面我们再介绍这个队列是怎么运作的。
取得Pod Info 后，依次运行刚才注册的预选与优选调度策略，最终选择出来合适的Node，然后调用Client go 的Bind 方法，将Pod 绑定到Node 上完成调度动作。
调度Pod Queue 构成
// NewConfigFactory initializes the default implementation of a Configurator. To encourage eventual privatization of the struct type, we only
// return the interface.
func NewConfigFactory(args *ConfigFactoryArgs) Configurator {
stopEverything := args.StopCh
if stopEverything == nil {
stopEverything = wait.NeverStop
}
schedulerCache := schedulerinternalcache.New(30*time.Second, stopEverything)
// storageClassInformer is only enabled through VolumeScheduling feature gate
var storageClassLister storagelisters.StorageClassLister
if args.StorageClassInformer != nil {
storageClassLister = args.StorageClassInformer.Lister()
}
c := &configFactory{
client: args.Client,
podLister: schedulerCache,
podQueue: internalqueue.NewSchedulingQueue(stopEverything),
nodeLister: args.NodeInformer.Lister(),
pVLister: args.PvInformer.Lister(),
pVCLister: args.PvcInformer.Lister(),
serviceLister: args.ServiceInformer.Lister(),
controllerLister: args.ReplicationControllerInformer.Lister(),
replicaSetLister: args.ReplicaSetInformer.Lister(),
statefulSetLister: args.StatefulSetInformer.Lister(),
pdbLister: args.PdbInformer.Lister(),
storageClassLister: storageClassLister,
schedulerCache: schedulerCache,
StopEverything: stopEverything,
schedulerName: args.SchedulerName,
hardPodAffinitySymmetricWeight: args.HardPodAffinitySymmetricWeight,
disablePreemption: args.DisablePreemption,
percentageOfNodesToScore: args.PercentageOfNodesToScore,
}
c.scheduledPodsHasSynced = args.PodInformer.Informer().HasSynced
// scheduled pod cache
args.PodInformer.Informer().AddEventHandler(
cache.FilteringResourceEventHandler{
FilterFunc: func(obj interface{}) bool {
switch t := obj.(type) {
case *v1.Pod:
return assignedPod(t)
case cache.DeletedFinalStateUnknown:
if pod, ok := t.Obj.(*v1.Pod); ok {
return assignedPod(pod)
}
runtime.HandleError(fmt.Errorf("unable to convert object %T to *v1.Pod for filtering scheduledPod in %T", obj, c))
return false
default:
runtime.HandleError(fmt.Errorf("unable to handle object for filtering scheduledPod in %T: %T", c, obj))
return false
}
},
Handler: cache.ResourceEventHandlerFuncs{
AddFunc: c.addPodToCache,
UpdateFunc: c.updatePodInCache,
DeleteFunc: c.deletePodFromCache,
},
},
)
// unscheduled pod queue
args.PodInformer.Informer().AddEventHandler(
cache.FilteringResourceEventHandler{
FilterFunc: func(obj interface{}) bool {
switch t := obj.(type) {
case *v1.Pod:
return !assignedPod(t) && responsibleForPod(t, args.SchedulerName)
case cache.DeletedFinalStateUnknown:
if pod, ok := t.Obj.(*v1.Pod); ok {
return !assignedPod(pod) && responsibleForPod(pod, args.SchedulerName)
}
runtime.HandleError(fmt.Errorf("unable to convert object %T to *v1.Pod for filtering unscheduledPod in %T", obj, c))
return false
default:
runtime.HandleError(fmt.Errorf("unable to handle object for filtering unscheduledPod in %T: %T", c, obj))
return false
}
},
Handler: cache.ResourceEventHandlerFuncs{
AddFunc: c.addPodToSchedulingQueue,
UpdateFunc: c.updatePodInSchedulingQueue,
DeleteFunc: c.deletePodFromSchedulingQueue,
},
},
)这里完成了针对Pod 的Watch，同时将未调度的Pod 放入未调度Queue 方便调度器进行调度。可以看到，这里同样适用的Client go Informer 机制来同步Pod 的信息。
PodFitsHostPorts
由于PreDicates非常多，我们就以检查 Pod 端口冲突为例看一下PreDicates 函数
// PodFitsHostPorts checks if a node has free ports for the requested pod ports.
func PodFitsHostPorts(pod *v1.Pod, meta PredicateMetadata, nodeInfo *schedulernodeinfo.NodeInfo) (bool, []PredicateFailureReason, error) {
var wantPorts []*v1.ContainerPort
if predicateMeta, ok := meta.(*predicateMetadata); ok {
wantPorts = predicateMeta.podPorts
} else {
// We couldn't parse metadata - fallback to computing it.
wantPorts = schedutil.GetContainerPorts(pod)
}
if len(wantPorts) == 0 {
return true, nil, nil
}
existingPorts := nodeInfo.UsedPorts()
// try to see whether existingPorts and wantPorts will conflict or not
if portsConflict(existingPorts, wantPorts) {
return false, []PredicateFailureReason{ErrPodNotFitsHostPorts}, nil
}
return true, nil, nil
}- 根据传入的Pod info 查看Pod 需要暴露的端口
- 根据Node info 判断当前Node 可用端口
- 判断是否被占用并返回结果
ImageLocalityPriority
func ImageLocalityPriorityMap(pod *v1.Pod, meta interface{}, nodeInfo *schedulernodeinfo.NodeInfo) (schedulerapi.HostPriority, error) {
node := nodeInfo.Node()
if node == nil {
return schedulerapi.HostPriority{}, fmt.Errorf("node not found")
}
var score int
if priorityMeta, ok := meta.(*priorityMetadata); ok {
score = calculatePriority(sumImageScores(nodeInfo, pod.Spec.Containers, priorityMeta.totalNumNodes))
} else {
// if we are not able to parse priority meta data, skip this priority
score = 0
}
return schedulerapi.HostPriority{
Host: node.Name,
Score: score,
}, nil
}Priority我们以镜像为例，可以看到，先根据Pod info 来查看需要哪些镜像，然后根据Node info 查看当前镜像是否存在，存在的越多打分越高。
