kube-scheduler是集群中Master节点的重要组件，其功能是根据调度算法计算，将Pod合理bind到Kubernetes集群中的各个node节点上，scheduler是怎么调度工作的？没什么文档比看源码逻辑更直接了，由于能力有限且源码庞大复杂，如有错误之处还望指正。
k8s版本：1.13
代码下载: go get k8s.io/kubernetes
scheduler代码入口位置：kubernetes/cmd/kube-scheduler/scheduler.go
func main() {
rand.Seed(time.Now().UnixNano())
command := app.NewSchedulerCommand()
pflag.CommandLine.SetNormalizeFunc(utilflag.WordSepNormalizeFunc)
logs.InitLogs()
defer logs.FlushLogs()
if err := command.Execute(); err != nil {
fmt.Fprintf(os.Stderr, "%v\n", err)
os.Exit(1)
}
}Scheduler命令启动执行NewSchedulerCommand创建一个新的Scheduler调度，NewSchedulerCommand是干嘛的，接着看看，NewSchedulerCommand部分代码：kubernetes/cmd/kube-scheduler/app/server.go
func NewSchedulerCommand() *cobra.Command {
opts, err := options.NewOptions()//读取初始化参数
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)
}
},
}
fs := cmd.Flags()
namedFlagSets := opts.Flags()
verflag.AddFlags(namedFlagSets.FlagSet("global"))
globalflag.AddGlobalFlags(namedFlagSets.FlagSet("global"), cmd.Name())
for _, f := range namedFlagSets.FlagSets {
fs.AddFlagSet(f)
}
usageFmt := "Usage:\n %s\n"
cols, _, _ := apiserverflag.TerminalSize(cmd.OutOrStdout())
cmd.SetUsageFunc(func(cmd *cobra.Command) error {
fmt.Fprintf(cmd.OutOrStderr(), usageFmt, cmd.UseLine())
apiserverflag.PrintSections(cmd.OutOrStderr(), namedFlagSets, cols)
return nil
})
cmd.SetHelpFunc(func(cmd *cobra.Command, args []string) {
fmt.Fprintf(cmd.OutOrStdout(), "%s\n\n"+usageFmt, cmd.Long, cmd.UseLine())
apiserverflag.PrintSections(cmd.OutOrStdout(), namedFlagSets, cols)
})
cmd.MarkFlagFilename("config", "yaml", "yml", "json")
return cmd
}NewSchedulerCommand中
1、NewOptions进行读取参数实例化，其中参数缺省值在kubernetes/vendor/k8s.io/kube-scheduler/config/v1alpha1/types.go定义，
更多的默认参数可以通过命令kube-scheduler --help来查看。
2、runCommand来启动一个调度器，接着看runCommand的函数段：
func runCommand(cmd *cobra.Command, args []string, opts *options.Options) error {
verflag.PrintAndExitIfRequested()
utilflag.PrintFlags(cmd.Flags())
if len(args) != 0 {
fmt.Fprint(os.Stderr, "arguments are not supported\n")
}
if errs := opts.Validate(); len(errs) > 0 {
fmt.Fprintf(os.Stderr, "%v\n", utilerrors.NewAggregate(errs))
os.Exit(1)
}
if len(opts.WriteConfigTo) > 0 {
if err := options.WriteConfigFile(opts.WriteConfigTo, &opts.ComponentConfig); err != nil {
fmt.Fprintf(os.Stderr, "%v\n", err)
os.Exit(1)
}
klog.Infof("Wrote configuration to: %s\n", opts.WriteConfigTo)
}
c, err := opts.Config()
if err != nil {
fmt.Fprintf(os.Stderr, "%v\n", err)
os.Exit(1)
}
stopCh := make(chan struct{})
// Get the completed config
cc := c.Complete()
// To help debugging, immediately log version
klog.Infof("Version: %+v", version.Get())
// Apply algorithms based on feature gates.
// TODO: make configurable?
algorithmprovider.ApplyFeatureGates()
// Configz registration.
if cz, err := configz.New("componentconfig"); err == nil {
cz.Set(cc.ComponentConfig)
} else {
return fmt.Errorf("unable to register configz: %s", err)
}
return Run(cc, stopCh)
}
runCommand主要是读取schedule的启动配置参数，最后根据配置参数运行Run，并且根据Run处理返回相应的错误err。再继续往下看看Run干了什么：
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
}
// Prepare the event broadcaster.
if cc.Broadcaster != nil && cc.EventClient != nil {
cc.Broadcaster.StartLogging(klog.V(6).Infof)
cc.Broadcaster.StartRecordingToSink(&v1core.EventSinkImpl{Interface: cc.EventClient.Events("")})
}
// Setup healthz checks.
var checks []healthz.HealthzChecker
if cc.ComponentConfig.LeaderElection.LeaderElect {
checks = append(checks, cc.LeaderElection.WatchDog)
}
// Start up the healthz server.
if cc.InsecureServing != nil {
separateMetrics := cc.InsecureMetricsServing != nil
handler := buildHandlerChain(newHealthzHandler(&cc.ComponentConfig, separateMetrics, checks...), nil, nil)
if err := cc.InsecureServing.Serve(handler, 0, stopCh); err != nil {
return fmt.Errorf("failed to start healthz server: %v", err)
}
}
if cc.InsecureMetricsServing != nil {
handler := buildHandlerChain(newMetricsHandler(&cc.ComponentConfig), nil, nil)
if err := cc.InsecureMetricsServing.Serve(handler, 0, stopCh); err != nil {
return fmt.Errorf("failed to start metrics server: %v", err)
}
}
if cc.SecureServing != nil {
handler := buildHandlerChain(newHealthzHandler(&cc.ComponentConfig, false, checks...), cc.Authentication.Authenticator, cc.Authorization.Authorizer)
if err := cc.SecureServing.Serve(handler, 0, stopCh); err != nil {
// fail early for secure handlers, removing the old error loop from above
return fmt.Errorf("failed to start healthz server: %v", 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")
}Run中根据config配置：
1、scheduler.New实例化一个新的调度器实例并返回sched
2、配置广播和健康检查以及metric信息（普罗米修斯监控使用）的端口：cc.InsecureServing.Serve（默认InsecureServing启动的监听端口为10251）
3、启动所有informer，其中单独执行PodInformer：cc.PodInformer.Informer().Run(stopCh)，PodInformer提供pods信息的lister的访问入口。
PS:Informer 是 Client-go 中的一个核心工具包，Informer 最基本 的功能就是 List/Get Kubernetes 中的 Object，Informer的详细信息可以参考这篇文章。
4、调度前先执行kube-controller的controller.WaitForCacheSync，等待 pod的 informer 同步。
5、scheduler的高可用leader选举(--leader-elect)，集群高可用部署时scheduler必须选举leader，默认即true。
6、运行真正的调度 run 函数，sched.Run()执行调度pod。
接着来看，第一步的scheduler.New是怎么来工作的，然后再看下最后一步的Run是怎么调度的，先跳转到scheduler.New代码部分：kubernetes/pkg/scheduler/scheduler.go
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
}1、根据New的传参构建factory.NewConfigFactory配置configurator，factory.NewConfigFactory为一系列Informer初始化了回调函数，其中最重要的是PodInformer的两个回调函数，将已调度和未调度的Pod分别存入缓存和队列中。
// 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,
},
},
)
// ScheduledPodLister is something we provide to plug-in functions that
// they may need to call.
c.scheduledPodLister = assignedPodLister{args.PodInformer.Lister()}
args.NodeInformer.Informer().AddEventHandler(
cache.ResourceEventHandlerFuncs{
AddFunc: c.addNodeToCache,
UpdateFunc: c.updateNodeInCache,
DeleteFunc: c.deleteNodeFromCache,
},
)
args.PvInformer.Informer().AddEventHandler(
cache.ResourceEventHandlerFuncs{
// MaxPDVolumeCountPredicate: since it relies on the counts of PV.
AddFunc: c.onPvAdd,
UpdateFunc: c.onPvUpdate,
},
)
// This is for MaxPDVolumeCountPredicate: add/delete PVC will affect counts of PV when it is bound.
args.PvcInformer.Informer().AddEventHandler(
cache.ResourceEventHandlerFuncs{
AddFunc: c.onPvcAdd,
UpdateFunc: c.onPvcUpdate,
},
)
// This is for ServiceAffinity: affected by the selector of the service is updated.
args.ServiceInformer.Informer().AddEventHandler(
cache.ResourceEventHandlerFuncs{
AddFunc: c.onServiceAdd,
UpdateFunc: c.onServiceUpdate,
DeleteFunc: c.onServiceDelete,
},
)
// Setup volume binder
c.volumeBinder = volumebinder.NewVolumeBinder(args.Client, args.NodeInformer, args.PvcInformer, args.PvInformer, args.StorageClassInformer, time.Duration(args.BindTimeoutSeconds)*time.Second)
args.StorageClassInformer.Informer().AddEventHandler(
cache.ResourceEventHandlerFuncs{
AddFunc: c.onStorageClassAdd,
},
)
// Setup cache debugger
debugger := cachedebugger.New(
args.NodeInformer.Lister(),
args.PodInformer.Lister(),
c.schedulerCache,
c.podQueue,
)
debugger.ListenForSignal(c.StopEverything)
go func() {
<-c.StopEverything
c.podQueue.Close()
}()
return c
}2、根据Provider 和 configMap 来创建对应的调度器以及初始化环境变量、配置文件策略。
3、然后调用NewFromConfig方法，通过这个Config创建一个scheduler实例并返回sched
run的代码段
// Run begins watching and scheduling. It waits for cache to be synced, then starts a goroutine and returns immediately.
func (sched *Scheduler) Run() {
if !sched.config.WaitForCacheSync() {
return
}
go wait.Until(sched.scheduleOne, 0, sched.config.StopEverything)
}Scheduler 通过 wait.Until() 工具，不停得调用 Scheduler.scheduleOne() 方法直到收到停止信号。
看看scheduleOne代码段，这是最终调度Pod的最终函数：
// 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)
if err != nil {
// schedule() may have failed because the pod would not fit on any host, so we try to
// preempt, with the expectation that the next time the pod is tried for scheduling it
// will fit due to the preemption. It is also possible that a different pod will schedule
// into the resources that were preempted, but this is harmless.
if fitError, ok := err.(*core.FitError); ok {
if !util.PodPriorityEnabled() || sched.config.DisablePreemption {
klog.V(3).Infof("Pod priority feature is not enabled or preemption is disabled by scheduler configuration." +
" No preemption is performed.")
} else {
preemptionStartTime := time.Now()
sched.preempt(pod, fitError)
metrics.PreemptionAttempts.Inc()
metrics.SchedulingAlgorithmPremptionEvaluationDuration.Observe(metrics.SinceInMicroseconds(preemptionStartTime))
metrics.SchedulingLatency.WithLabelValues(metrics.PreemptionEvaluation).Observe(metrics.SinceInSeconds(preemptionStartTime))
}
// Pod did not fit anywhere, so it is counted as a failure. If preemption
// succeeds, the pod should get counted as a success the next time we try to
// schedule it. (hopefully)
metrics.PodScheduleFailures.Inc()
} else {
klog.Errorf("error selecting node for pod: %v", err)
metrics.PodScheduleErrors.Inc()
}
return
}
metrics.SchedulingAlgorithmLatency.Observe(metrics.SinceInMicroseconds(start))
// Tell the cache to assume that a pod now is running on a given node, even though it hasn't been bound yet.
// This allows us to keep scheduling without waiting on binding to occur.
assumedPod := pod.DeepCopy()
// Assume volumes first before assuming the pod.
//
// If all volumes are completely bound, then allBound is true and binding will be skipped.
//
// Otherwise, binding of volumes is started after the pod is assumed, but before pod binding.
//
// This function modifies 'assumedPod' if volume binding is required.
allBound, err := sched.assumeVolumes(assumedPod, scheduleResult.SuggestedHost)
if err != nil {
klog.Errorf("error assuming volumes: %v", err)
metrics.PodScheduleErrors.Inc()
return
}
// Run "reserve" plugins.
for _, pl := range plugins.ReservePlugins() {
if err := pl.Reserve(plugins, assumedPod, scheduleResult.SuggestedHost); err != nil {
klog.Errorf("error while running %v reserve plugin for pod %v: %v", pl.Name(), assumedPod.Name, err)
sched.recordSchedulingFailure(assumedPod, err, SchedulerError,
fmt.Sprintf("reserve plugin %v failed", pl.Name()))
metrics.PodScheduleErrors.Inc()
return
}
}
// assume modifies `assumedPod` by setting NodeName=scheduleResult.SuggestedHost
err = sched.assume(assumedPod, scheduleResult.SuggestedHost)
if err != nil {
klog.Errorf("error assuming pod: %v", err)
metrics.PodScheduleErrors.Inc()
return
}
// bind the pod to its host asynchronously (we can do this b/c of the assumption step above).
go func() {
// Bind volumes first before Pod
if !allBound {
err := sched.bindVolumes(assumedPod)
if err != nil {
klog.Errorf("error binding volumes: %v", err)
metrics.PodScheduleErrors.Inc()
return
}
}
// Run "prebind" plugins.
for _, pl := range plugins.PrebindPlugins() {
approved, err := pl.Prebind(plugins, assumedPod, scheduleResult.SuggestedHost)
if err != nil {
approved = false
klog.Errorf("error while running %v prebind plugin for pod %v: %v", pl.Name(), assumedPod.Name, err)
metrics.PodScheduleErrors.Inc()
}
if !approved {
sched.Cache().ForgetPod(assumedPod)
var reason string
if err == nil {
msg := fmt.Sprintf("prebind plugin %v rejected pod %v.", pl.Name(), assumedPod.Name)
klog.V(4).Infof(msg)
err = errors.New(msg)
reason = v1.PodReasonUnschedulable
} else {
reason = SchedulerError
}
sched.recordSchedulingFailure(assumedPod, err, reason, err.Error())
return
}
}
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,
},
})
metrics.E2eSchedulingLatency.Observe(metrics.SinceInMicroseconds(start))
if err != nil {
klog.Errorf("error binding pod: %v", err)
metrics.PodScheduleErrors.Inc()
} else {
klog.V(2).Infof("pod %v/%v is bound successfully on node %v, %d nodes evaluated, %d nodes were found feasible", assumedPod.Namespace, assumedPod.Name, scheduleResult.SuggestedHost, scheduleResult.EvaluatedNodes, scheduleResult.FeasibleNodes)
metrics.PodScheduleSuccesses.Inc()
}
}()
}
scheduleOne是串行调度的，每次调度一个pod到合适的node节点上，
1、sched.config.NextPod从podQueue队列中取出下一个Pod。如果这个Pod正在删除，则跳过。
2.1、sched.schedule进行算法调度这个Pod，如果调度分配失败（比如没有node资源可调度）则进行记录，并且如果开启抢占配置（preemption），失败调度的pod会尝试抢占记录，下次调度优先调度，然后记录调度成功和调度失败的次数，以及调度分配耗时。
// schedule implements the scheduling algorithm and returns the suggested result(host,
// evaluated nodes number,feasible nodes number).
func (sched *Scheduler) schedule(pod *v1.Pod) (core.ScheduleResult, error) {
result, err := sched.config.Algorithm.Schedule(pod, sched.config.NodeLister)
if err != nil {
pod = pod.DeepCopy()
sched.recordSchedulingFailure(pod, err, v1.PodReasonUnschedulable, err.Error())
return core.ScheduleResult{}, err
}
return result, err
}2.2 sched.config.Algorithm.Schedule对node列表进行调度，如果调度成功则返回一个调度节点的name，否则返回相应的错误信息。
// Schedule tries to schedule the given pod to one of the nodes in the node list.
// If it succeeds, it will return the name of the node.
// If it fails, it will return a FitError error with reasons.
func (g *genericScheduler) Schedule(pod *v1.Pod, nodeLister algorithm.NodeLister) (result ScheduleResult, err error) {
trace := utiltrace.New(fmt.Sprintf("Scheduling %s/%s", pod.Namespace, pod.Name))
defer trace.LogIfLong(100 * time.Millisecond)
if err := podPassesBasicChecks(pod, g.pvcLister); err != nil {
return result, err
}
nodes, err := nodeLister.List()
if err != nil {
return result, err
}
if len(nodes) == 0 {
return result, ErrNoNodesAvailable
}
if err := g.snapshot(); err != nil {
return result, err
}
trace.Step("Computing predicates")
startPredicateEvalTime := time.Now()
filteredNodes, failedPredicateMap, err := g.findNodesThatFit(pod, nodes)
if err != nil {
return result, err
}
if len(filteredNodes) == 0 {
return result, &FitError{
Pod: pod,
NumAllNodes: len(nodes),
FailedPredicates: failedPredicateMap,
}
}
metrics.SchedulingAlgorithmPredicateEvaluationDuration.Observe(metrics.SinceInMicroseconds(startPredicateEvalTime))
metrics.SchedulingLatency.WithLabelValues(metrics.PredicateEvaluation).Observe(metrics.SinceInSeconds(startPredicateEvalTime))
trace.Step("Prioritizing")
startPriorityEvalTime := time.Now()
// When only one node after predicate, just use it.
if len(filteredNodes) == 1 {
metrics.SchedulingAlgorithmPriorityEvaluationDuration.Observe(metrics.SinceInMicroseconds(startPriorityEvalTime))
return ScheduleResult{
SuggestedHost: filteredNodes[0].Name,
EvaluatedNodes: 1 + len(failedPredicateMap),
FeasibleNodes: 1,
}, nil
}
metaPrioritiesInterface := g.priorityMetaProducer(pod, g.cachedNodeInfoMap)
priorityList, err := PrioritizeNodes(pod, g.cachedNodeInfoMap, metaPrioritiesInterface, g.prioritizers, filteredNodes, g.extenders)
if err != nil {
return result, err
}
metrics.SchedulingAlgorithmPriorityEvaluationDuration.Observe(metrics.SinceInMicroseconds(startPriorityEvalTime))
metrics.SchedulingLatency.WithLabelValues(metrics.PriorityEvaluation).Observe(metrics.SinceInSeconds(startPriorityEvalTime))
trace.Step("Selecting host")
host, err := g.selectHost(priorityList)
return ScheduleResult{
SuggestedHost: host,
EvaluatedNodes: len(filteredNodes) + len(failedPredicateMap),
FeasibleNodes: len(filteredNodes),
}, err
}上面Schedule调度中:
2.2.1.获取可用的node列表
2.2.2.先进行Predicates预选（findNodesThatFit）调度算法计算，刷选出合适的filteredNodes，看看预选的代码段
func (g *genericScheduler) findNodesThatFit(pod *v1.Pod, nodes []*v1.Node) ([]*v1.Node, FailedPredicateMap, error) {
var filtered []*v1.Node
failedPredicateMap := FailedPredicateMap{}
if len(g.predicates) == 0 {
filtered = nodes
} else {
allNodes := int32(g.cache.NodeTree().NumNodes())
numNodesToFind := g.numFeasibleNodesToFind(allNodes)
// Create filtered list with enough space to avoid growing it
// and allow assigning.
filtered = make([]*v1.Node, numNodesToFind)
errs := errors.MessageCountMap{}
var (
predicateResultLock sync.Mutex
filteredLen int32
)
ctx, cancel := context.WithCancel(context.Background())
// We can use the same metadata producer for all nodes.
meta := g.predicateMetaProducer(pod, g.cachedNodeInfoMap)
checkNode := func(i int) {
nodeName := g.cache.NodeTree().Next()
fits, failedPredicates, err := podFitsOnNode(
pod,
meta,
g.cachedNodeInfoMap[nodeName],
g.predicates,
g.schedulingQueue,
g.alwaysCheckAllPredicates,
)
if err != nil {
predicateResultLock.Lock()
errs[err.Error()]++
predicateResultLock.Unlock()
return
}
if fits {
length := atomic.AddInt32(&filteredLen, 1)
if length > numNodesToFind {
cancel()
atomic.AddInt32(&filteredLen, -1)
} else {
filtered[length-1] = g.cachedNodeInfoMap[nodeName].Node()
}
} else {
predicateResultLock.Lock()
failedPredicateMap[nodeName] = failedPredicates
predicateResultLock.Unlock()
}
}
// Stops searching for more nodes once the configured number of feasible nodes
// are found.
workqueue.ParallelizeUntil(ctx, 16, int(allNodes), checkNode)
filtered = filtered[:filteredLen]
if len(errs) > 0 {
return []*v1.Node{}, FailedPredicateMap{}, errors.CreateAggregateFromMessageCountMap(errs)
}
}
if len(filtered) > 0 && len(g.extenders) != 0 {
for _, extender := range g.extenders {
if !extender.IsInterested(pod) {
continue
}
filteredList, failedMap, err := extender.Filter(pod, filtered, g.cachedNodeInfoMap)
if err != nil {
if extender.IsIgnorable() {
klog.Warningf("Skipping extender %v as it returned error %v and has ignorable flag set",
extender, err)
continue
} else {
return []*v1.Node{}, FailedPredicateMap{}, err
}
}
for failedNodeName, failedMsg := range failedMap {
if _, found := failedPredicateMap[failedNodeName]; !found {
failedPredicateMap[failedNodeName] = []predicates.PredicateFailureReason{}
}
failedPredicateMap[failedNodeName] = append(failedPredicateMap[failedNodeName], predicates.NewFailureReason(failedMsg))
}
filtered = filteredList
if len(filtered) == 0 {
break
}
}
}
return filtered, failedPredicateMap, nil
}2.2.3 numFeasibleNodesToFind刷选出可用的node数量
2.2.4 podFitsOnNode判断node是否合适在node节点上。TODO：kubernetes的extender的使用了解。
2.2.5.如果filteredNodes数量大于2，进行权重优选（PrioritizeNodes）调度算法计算刷选
func PrioritizeNodes(
pod *v1.Pod,
nodeNameToInfo map[string]*schedulernodeinfo.NodeInfo,
meta interface{},
priorityConfigs []algorithm.PriorityConfig,
nodes []*v1.Node,
extenders []algorithm.SchedulerExtender,
) (schedulerapi.HostPriorityList, error) {
// If no priority configs are provided, then the EqualPriority function is applied
// This is required to generate the priority list in the required format
if len(priorityConfigs) == 0 && len(extenders) == 0 {
result := make(schedulerapi.HostPriorityList, 0, len(nodes))
for i := range nodes {
hostPriority, err := EqualPriorityMap(pod, meta, nodeNameToInfo[nodes[i].Name])
if err != nil {
return nil, err
}
result = append(result, hostPriority)
}
return result, nil
}
var (
mu = sync.Mutex{}
wg = sync.WaitGroup{}
errs []error
)
appendError := func(err error) {
mu.Lock()
defer mu.Unlock()
errs = append(errs, err)
}
results := make([]schedulerapi.HostPriorityList, len(priorityConfigs), len(priorityConfigs))
// DEPRECATED: we can remove this when all priorityConfigs implement the
// Map-Reduce pattern.
for i := range priorityConfigs {
if priorityConfigs[i].Function != nil {
wg.Add(1)
go func(index int) {
defer wg.Done()
var err error
results[index], err = priorityConfigs[index].Function(pod, nodeNameToInfo, nodes)
if err != nil {
appendError(err)
}
}(i)
} else {
results[i] = make(schedulerapi.HostPriorityList, len(nodes))
}
}
workqueue.ParallelizeUntil(context.TODO(), 16, len(nodes), func(index int) {
nodeInfo := nodeNameToInfo[nodes[index].Name]
for i := range priorityConfigs {
if priorityConfigs[i].Function != nil {
continue
}
var err error
results[i][index], err = priorityConfigs[i].Map(pod, meta, nodeInfo)
if err != nil {
appendError(err)
results[i][index].Host = nodes[index].Name
}
}
})
for i := range priorityConfigs {
if priorityConfigs[i].Reduce == nil {
continue
}
wg.Add(1)
go func(index int) {
defer wg.Done()
if err := priorityConfigs[index].Reduce(pod, meta, nodeNameToInfo, results[index]); err != nil {
appendError(err)
}
if klog.V(10) {
for _, hostPriority := range results[index] {
klog.Infof("%v -> %v: %v, Score: (%d)", util.GetPodFullName(pod), hostPriority.Host, priorityConfigs[index].Name, hostPriority.Score)
}
}
}(i)
}
// Wait for all computations to be finished.
wg.Wait()
if len(errs) != 0 {
return schedulerapi.HostPriorityList{}, errors.NewAggregate(errs)
}
// Summarize all scores.
result := make(schedulerapi.HostPriorityList, 0, len(nodes))
for i := range nodes {
result = append(result, schedulerapi.HostPriority{Host: nodes[i].Name, Score: 0})
for j := range priorityConfigs {
result[i].Score += results[j][i].Score * priorityConfigs[j].Weight
}
}
if len(extenders) != 0 && nodes != nil {
combinedScores := make(map[string]int, len(nodeNameToInfo))
for i := range extenders {
if !extenders[i].IsInterested(pod) {
continue
}
wg.Add(1)
go func(extIndex int) {
defer wg.Done()
prioritizedList, weight, err := extenders[extIndex].Prioritize(pod, nodes)
if err != nil {
// Prioritization errors from extender can be ignored, let k8s/other extenders determine the priorities
return
}
mu.Lock()
for i := range *prioritizedList {
host, score := (*prioritizedList)[i].Host, (*prioritizedList)[i].Score
if klog.V(10) {
klog.Infof("%v -> %v: %v, Score: (%d)", util.GetPodFullName(pod), host, extenders[extIndex].Name(), score)
}
combinedScores[host] += score * weight
}
mu.Unlock()
}(i)
}
// wait for all go routines to finish
wg.Wait()
for i := range result {
result[i].Score += combinedScores[result[i].Host]
}
}
if klog.V(10) {
for i := range result {
klog.Infof("Host %s => Score %d", result[i].Host, result[i].Score)
}
}
return result, nil
}2.2.6 selectHost() 如果优选出的多个得分相同的 Node，则随机选取一个 Node。
3、调度分配好后pod.DeepCopy()更新到缓存已分配记录（assumedPod）。
4、如果有volume的设置，在bind pod之前先进行volume的绑定。
5、异步bind pod到分配好的node节点上，调用 kube-apiserver API，将 Pod 绑定到选出的 Node，之后 kube-apiserver 会将元数据写入 etcd 中。
大致刷选流程图：
总结：
kube-scheduler 作为 Kubernetes master上一个单独的进程提供调度服务，通过informer的list-watch机制，从apiserver端获取数据并缓存。
获取到待调度的 Pod 后，执行Schedule 方法进行调度，整个调度过程分两个关键步骤：Predicates 和 Priorities (其中刷选的调度策略policy可以通过启动参数--policy-config-file进行json格式自定义调度策略，如上流程图的policy摘至官方代码给的示例参数，默认调度策略是defaultProvider, defaultPredicates, defaultPriorities )，最终选出一个最适合该 Pod 的 Node，更新 SchedulerCache 中 Pod 的状态 (AssumePod)，标志该 Pod 为 scheduled，并更新到 NodeInfo 中。
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