Kubernetes Scheduler Extensibility

func init() {
	registerAlgorithmProvider(defaultPredicates(), defaultPriorities())
}

func defaultPredicates() sets.String {
	return sets.NewString(
		predicates.NoVolumeZoneConflictPred,
		predicates.MaxEBSVolumeCountPred,
		predicates.MaxGCEPDVolumeCountPred,
		predicates.MaxAzureDiskVolumeCountPred,
		predicates.MaxCSIVolumeCountPred,
		predicates.MatchInterPodAffinityPred,
		predicates.NoDiskConflictPred,
		predicates.GeneralPred,
		predicates.PodToleratesNodeTaintsPred,
		predicates.CheckVolumeBindingPred,
		predicates.CheckNodeUnschedulablePred,
	)
}

func defaultPriorities() sets.String {
	return sets.NewString(
		priorities.SelectorSpreadPriority,
		priorities.InterPodAffinityPriority,
		priorities.LeastRequestedPriority,
		priorities.BalancedResourceAllocation,
		priorities.NodePreferAvoidPodsPriority,
		priorities.NodeAffinityPriority,
		priorities.TaintTolerationPriority,
		priorities.ImageLocalityPriority,
	)
}

func registerAlgorithmProvider(predSet, priSet sets.String) {
	// Registers algorithm providers. By default we use 'DefaultProvider', but user can specify one to be used
	// by specifying flag.
	scheduler.RegisterAlgorithmProvider(scheduler.DefaultProvider, predSet, priSet)
	// Cluster autoscaler friendly scheduling algorithm.
	scheduler.RegisterAlgorithmProvider(ClusterAutoscalerProvider, predSet,
		copyAndReplace(priSet, priorities.LeastRequestedPriority, priorities.MostRequestedPriority))
}

const (
	// DefaultProvider defines the default algorithm provider name.
	DefaultProvider = "DefaultProvider"
)

func init() {
    ...
	// Fit is determined by resource availability.
	// This predicate is actually a default predicate, because it is invoked from
	// predicates.GeneralPredicates()
	scheduler.RegisterFitPredicate(predicates.PodFitsResourcesPred, predicates.PodFitsResources)
}

func init() {
    ...
	// Prioritizes nodes that have labels matching NodeAffinity
	scheduler.RegisterPriorityMapReduceFunction(priorities.NodeAffinityPriority, priorities.CalculateNodeAffinityPriorityMap, priorities.CalculateNodeAffinityPriorityReduce, 1)
}

// PodFitsResources checks if a node has sufficient resources, such as cpu, memory, gpu, opaque int resources etc to run a pod.
// First return value indicates whether a node has sufficient resources to run a pod while the second return value indicates the
// predicate failure reasons if the node has insufficient resources to run the pod.
func PodFitsResources(pod *v1.Pod, meta Metadata, nodeInfo *schedulernodeinfo.NodeInfo) (bool, []PredicateFailureReason, error) {
	node := nodeInfo.Node()
	if node == nil {
		return false, nil, fmt.Errorf("node not found")
	}

	var predicateFails []PredicateFailureReason
	allowedPodNumber := nodeInfo.AllowedPodNumber()
	if len(nodeInfo.Pods())+1 > allowedPodNumber {
		predicateFails = append(predicateFails, NewInsufficientResourceError(v1.ResourcePods, 1, int64(len(nodeInfo.Pods())), int64(allowedPodNumber)))
	}

	// No extended resources should be ignored by default.
	ignoredExtendedResources := sets.NewString()

	var podRequest *schedulernodeinfo.Resource
	if predicateMeta, ok := meta.(*predicateMetadata); ok && predicateMeta.podFitsResourcesMetadata != nil {
		podRequest = predicateMeta.podFitsResourcesMetadata.podRequest
		if predicateMeta.podFitsResourcesMetadata.ignoredExtendedResources != nil {
			ignoredExtendedResources = predicateMeta.podFitsResourcesMetadata.ignoredExtendedResources
		}
	} else {
		// We couldn't parse metadata - fallback to computing it.
		podRequest = GetResourceRequest(pod)
	}
	if podRequest.MilliCPU == 0 &&
		podRequest.Memory == 0 &&
		podRequest.EphemeralStorage == 0 &&
		len(podRequest.ScalarResources) == 0 {
		return len(predicateFails) == 0, predicateFails, nil
	}

	allocatable := nodeInfo.AllocatableResource()
	if allocatable.MilliCPU < podRequest.MilliCPU+nodeInfo.RequestedResource().MilliCPU {
		predicateFails = append(predicateFails, NewInsufficientResourceError(v1.ResourceCPU, podRequest.MilliCPU, nodeInfo.RequestedResource().MilliCPU, allocatable.MilliCPU))
	}
	if allocatable.Memory < podRequest.Memory+nodeInfo.RequestedResource().Memory {
		predicateFails = append(predicateFails, NewInsufficientResourceError(v1.ResourceMemory, podRequest.Memory, nodeInfo.RequestedResource().Memory, allocatable.Memory))
	}
	if allocatable.EphemeralStorage < podRequest.EphemeralStorage+nodeInfo.RequestedResource().EphemeralStorage {
		predicateFails = append(predicateFails, NewInsufficientResourceError(v1.ResourceEphemeralStorage, podRequest.EphemeralStorage, nodeInfo.RequestedResource().EphemeralStorage, allocatable.EphemeralStorage))
	}

	for rName, rQuant := range podRequest.ScalarResources {
		if v1helper.IsExtendedResourceName(rName) {
			// If this resource is one of the extended resources that should be
			// ignored, we will skip checking it.
			if ignoredExtendedResources.Has(string(rName)) {
				continue
			}
		}
		if allocatable.ScalarResources[rName] < rQuant+nodeInfo.RequestedResource().ScalarResources[rName] {
			predicateFails = append(predicateFails, NewInsufficientResourceError(rName, podRequest.ScalarResources[rName], nodeInfo.RequestedResource().ScalarResources[rName], allocatable.ScalarResources[rName]))
		}
	}

	if klog.V(10) {
		if len(predicateFails) == 0 {
			// We explicitly don't do klog.V(10).Infof() to avoid computing all the parameters if this is
			// not logged. There is visible performance gain from it.
			klog.Infof("Schedule Pod %+v on Node %+v is allowed, Node is running only %v out of %v Pods.",
				podName(pod), node.Name, len(nodeInfo.Pods()), allowedPodNumber)
		}
	}
	return len(predicateFails) == 0, predicateFails, nil
}

// CalculateNodeAffinityPriorityMap prioritizes nodes according to node affinity scheduling preferences
// indicated in PreferredDuringSchedulingIgnoredDuringExecution. Each time a node matches a preferredSchedulingTerm,
// it will get an add of preferredSchedulingTerm.Weight. Thus, the more preferredSchedulingTerms
// the node satisfies and the more the preferredSchedulingTerm that is satisfied weights, the higher
// score the node gets.
func CalculateNodeAffinityPriorityMap(pod *v1.Pod, meta interface{}, nodeInfo *schedulernodeinfo.NodeInfo) (framework.NodeScore, error) {
	node := nodeInfo.Node()
	if node == nil {
		return framework.NodeScore{}, fmt.Errorf("node not found")
	}

	// default is the podspec.
	affinity := pod.Spec.Affinity
	if priorityMeta, ok := meta.(*priorityMetadata); ok {
		// We were able to parse metadata, use affinity from there.
		affinity = priorityMeta.affinity
	}

	var count int32
	// A nil element of PreferredDuringSchedulingIgnoredDuringExecution matches no objects.
	// An element of PreferredDuringSchedulingIgnoredDuringExecution that refers to an
	// empty PreferredSchedulingTerm matches all objects.
	if affinity != nil && affinity.NodeAffinity != nil && affinity.NodeAffinity.PreferredDuringSchedulingIgnoredDuringExecution != nil {
		// Match PreferredDuringSchedulingIgnoredDuringExecution term by term.
		for i := range affinity.NodeAffinity.PreferredDuringSchedulingIgnoredDuringExecution {
			preferredSchedulingTerm := &affinity.NodeAffinity.PreferredDuringSchedulingIgnoredDuringExecution[i]
			if preferredSchedulingTerm.Weight == 0 {
				continue
			}

			// TODO: Avoid computing it for all nodes if this becomes a performance problem.
			nodeSelector, err := v1helper.NodeSelectorRequirementsAsSelector(preferredSchedulingTerm.Preference.MatchExpressions)
			if err != nil {
				return framework.NodeScore{}, err
			}
			if nodeSelector.Matches(labels.Set(node.Labels)) {
				count += preferredSchedulingTerm.Weight
			}
		}
	}

	return framework.NodeScore{
		Name:  node.Name,
		Score: int64(count),
	}, nil
}

// CalculateNodeAffinityPriorityReduce is a reduce function for node affinity priority calculation.
var CalculateNodeAffinityPriorityReduce = NormalizeReduce(framework.MaxNodeScore, false)

// Fit is determined by resource availability.
// This predicate is actually a default predicate, because it is invoked from
// predicates.GeneralPredicates()
scheduler.RegisterFitPredicate(predicates.PodFitsResourcesPred, predicates.PodFitsResources)

...
// RegisterFitPredicate registers a fit predicate with the algorithm
// registry. Returns the name with which the predicate was registered.
func RegisterFitPredicate(name string, predicate predicates.FitPredicate) string {
	return RegisterFitPredicateFactory(name, func(AlgorithmFactoryArgs) predicates.FitPredicate { return predicate })
}

...
// RegisterFitPredicateFactory registers a fit predicate factory with the
// algorithm registry. Returns the name with which the predicate was registered.
func RegisterFitPredicateFactory(name string, predicateFactory FitPredicateFactory) string {
	schedulerFactoryMutex.Lock()
	defer schedulerFactoryMutex.Unlock()
	validateAlgorithmNameOrDie(name)
	fitPredicateMap[name] = predicateFactory
	return name
}

...
// Prioritizes nodes that have labels matching NodeAffinity
scheduler.RegisterPriorityMapReduceFunction(priorities.NodeAffinityPriority, priorities.CalculateNodeAffinityPriorityMap, priorities.CalculateNodeAffinityPriorityReduce, 1)

...
// RegisterPriorityMapReduceFunction registers a priority function with the algorithm registry. Returns the name,
// with which the function was registered.
func RegisterPriorityMapReduceFunction(
	name string,
	mapFunction priorities.PriorityMapFunction,
	reduceFunction priorities.PriorityReduceFunction,
	weight int) string {
	return RegisterPriorityConfigFactory(name, PriorityConfigFactory{
		MapReduceFunction: func(AlgorithmFactoryArgs) (priorities.PriorityMapFunction, priorities.PriorityReduceFunction) {
			return mapFunction, reduceFunction
		},
		Weight: int64(weight),
	})
}

...
// RegisterPriorityConfigFactory registers a priority config factory with its name.
func RegisterPriorityConfigFactory(name string, pcf PriorityConfigFactory) string {
	schedulerFactoryMutex.Lock()
	defer schedulerFactoryMutex.Unlock()
	validateAlgorithmNameOrDie(name)
	priorityFunctionMap[name] = pcf
	return name
}

...
// (g.predicates)
// podFitsOnNode checks whether a node given by NodeInfo satisfies the given predicate functions.
// For given pod, podFitsOnNode will check if any equivalent pod exists and try to reuse its cached
// predicate results as possible.
// This function is called from two different places: Schedule and Preempt.
// When it is called from Schedule, we want to test whether the pod is schedulable
// on the node with all the existing pods on the node plus higher and equal priority
// pods nominated to run on the node.
// When it is called from Preempt, we should remove the victims of preemption and
// add the nominated pods. Removal of the victims is done by SelectVictimsOnNode().
// It removes victims from meta and NodeInfo before calling this function.
func (g *genericScheduler) podFitsOnNode(
	ctx context.Context,
	state *framework.CycleState,
	pod *v1.Pod,
	meta predicates.Metadata,
	info *schedulernodeinfo.NodeInfo,
	alwaysCheckAllPredicates bool,
) (bool, []predicates.PredicateFailureReason, *framework.Status, error) {
	var failedPredicates []predicates.PredicateFailureReason
	var status *framework.Status

	podsAdded := false
	// We run predicates twice in some cases. If the node has greater or equal priority
	// nominated pods, we run them when those pods are added to meta and nodeInfo.
	// If all predicates succeed in this pass, we run them again when these
	// nominated pods are not added. This second pass is necessary because some
	// predicates such as inter-pod affinity may not pass without the nominated pods.
	// If there are no nominated pods for the node or if the first run of the
	// predicates fail, we don't run the second pass.
	// We consider only equal or higher priority pods in the first pass, because
	// those are the current "pod" must yield to them and not take a space opened
	// for running them. It is ok if the current "pod" take resources freed for
	// lower priority pods.
	// Requiring that the new pod is schedulable in both circumstances ensures that
	// we are making a conservative decision: predicates like resources and inter-pod
	// anti-affinity are more likely to fail when the nominated pods are treated
	// as running, while predicates like pod affinity are more likely to fail when
	// the nominated pods are treated as not running. We can't just assume the
	// nominated pods are running because they are not running right now and in fact,
	// they may end up getting scheduled to a different node.
	for i := 0; i < 2; i++ {
        ...
		for _, predicateKey := range predicates.Ordering() {
            ...
			if predicate, exist := g.predicates[predicateKey]; exist {
				fit, reasons, err = predicate(pod, metaToUse, nodeInfoToUse)
				if err != nil {
					return false, []predicates.PredicateFailureReason{}, nil, err
				}
                ...
			}
		}

	}

	return len(failedPredicates) == 0 && status.IsSuccess(), failedPredicates, status, nil
}

...
// (g.prioritizers)
// prioritizeNodes prioritizes the nodes by running the individual priority functions in parallel.
// Each priority function is expected to set a score of 0-10
// 0 is the lowest priority score (least preferred node) and 10 is the highest
// Each priority function can also have its own weight
// The node scores returned by the priority function are multiplied by the weights to get weighted scores
// All scores are finally combined (added) to get the total weighted scores of all nodes
func (g *genericScheduler) prioritizeNodes(
	ctx context.Context,
	state *framework.CycleState,
	pod *v1.Pod,
	meta interface{},
	nodes []*v1.Node,
) (framework.NodeScoreList, error) {

	workqueue.ParallelizeUntil(context.TODO(), 16, len(nodes), func(index int) {
		nodeInfo := g.nodeInfoSnapshot.NodeInfoMap[nodes[index].Name]
		for i := range g.prioritizers {
			var err error
			results[i][index], err = g.prioritizers[i].Map(pod, meta, nodeInfo)
			if err != nil {
				appendError(err)
				results[i][index].Name = nodes[index].Name
			}
		}
	})

	for i := range g.prioritizers {
		if g.prioritizers[i].Reduce == nil {
			continue
		}
		wg.Add(1)
		go func(index int) {
			metrics.SchedulerGoroutines.WithLabelValues("prioritizing_mapreduce").Inc()
			defer func() {
				metrics.SchedulerGoroutines.WithLabelValues("prioritizing_mapreduce").Dec()
				wg.Done()
			}()
			if err := g.prioritizers[index].Reduce(pod, meta, g.nodeInfoSnapshot, 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.Name, g.prioritizers[index].Name, hostPriority.Score)
				}
			}
		}(i)
	}
	// Wait for all computations to be finished.
	wg.Wait()
    ...
}

// k8s.io/kubernetes/pkg/scheduler/apis/config/legacy_types.go
// Extender holds the parameters used to communicate with the extender. If a verb is unspecified/empty,
// it is assumed that the extender chose not to provide that extension.
type Extender struct {
	// URLPrefix at which the extender is available
	URLPrefix string
	// Verb for the filter call, empty if not supported. This verb is appended to the URLPrefix when issuing the filter call to extender.
	FilterVerb string
	// Verb for the preempt call, empty if not supported. This verb is appended to the URLPrefix when issuing the preempt call to extender.
	PreemptVerb string
	// Verb for the prioritize call, empty if not supported. This verb is appended to the URLPrefix when issuing the prioritize call to extender.
	PrioritizeVerb string
	// The numeric multiplier for the node scores that the prioritize call generates.
	// The weight should be a positive integer
	Weight int64
	// Verb for the bind call, empty if not supported. This verb is appended to the URLPrefix when issuing the bind call to extender.
	// If this method is implemented by the extender, it is the extender's responsibility to bind the pod to apiserver. Only one extender
	// can implement this function.
	BindVerb string
	// EnableHTTPS specifies whether https should be used to communicate with the extender
	EnableHTTPS bool
	// TLSConfig specifies the transport layer security config
	TLSConfig *ExtenderTLSConfig
	// HTTPTimeout specifies the timeout duration for a call to the extender. Filter timeout fails the scheduling of the pod. Prioritize
	// timeout is ignored, k8s/other extenders priorities are used to select the node.
	HTTPTimeout time.Duration
	// NodeCacheCapable specifies that the extender is capable of caching node information,
	// so the scheduler should only send minimal information about the eligible nodes
	// assuming that the extender already cached full details of all nodes in the cluster
	NodeCacheCapable bool
	// ManagedResources is a list of extended resources that are managed by
	// this extender.
	// - A pod will be sent to the extender on the Filter, Prioritize and Bind
	//   (if the extender is the binder) phases iff the pod requests at least
	//   one of the extended resources in this list. If empty or unspecified,
	//   all pods will be sent to this extender.
	// - If IgnoredByScheduler is set to true for a resource, kube-scheduler
	//   will skip checking the resource in predicates.
	// +optional
	ManagedResources []ExtenderManagedResource
	// Ignorable specifies if the extender is ignorable, i.e. scheduling should not
	// fail when the extender returns an error or is not reachable.
	Ignorable bool
}

{
  "predicates": [
    {
      "name": "HostName"
    },
    {
      "name": "MatchNodeSelector"
    },
    {
      "name": "PodFitsResources"
    }
  ],
  "priorities": [
    {
      "name": "LeastRequestedPriority",
      "weight": 1
    }
  ],
  "extenders": [
    {
      "urlPrefix": "http://127.0.0.1:12345/api/scheduler",
      "filterVerb": "filter",
      "enableHttps": false
    }
  ]
}

// ExtenderArgs represents the arguments needed by the extender to filter/prioritize
// nodes for a pod.
type ExtenderArgs struct {
	// Pod being scheduled
	Pod *v1.Pod
	// List of candidate nodes where the pod can be scheduled; to be populated
	// only if ExtenderConfig.NodeCacheCapable == false
	Nodes *v1.NodeList
	// List of candidate node names where the pod can be scheduled; to be
	// populated only if ExtenderConfig.NodeCacheCapable == true
	NodeNames *[]string
}

// CreateFromConfig creates a scheduler from the configuration file
func (c *Configurator) CreateFromConfig(policy schedulerapi.Policy) (*Scheduler, error) {
	klog.V(2).Infof("Creating scheduler from configuration: %v", policy)
    ...
	var extenders []algorithm.SchedulerExtender
	if len(policy.Extenders) != 0 {
		ignoredExtendedResources := sets.NewString()
		var ignorableExtenders []algorithm.SchedulerExtender
		for ii := range policy.Extenders {
			klog.V(2).Infof("Creating extender with config %+v", policy.Extenders[ii])
			extender, err := core.NewHTTPExtender(&policy.Extenders[ii])
			if err != nil {
				return nil, err
			}
			if !extender.IsIgnorable() {
				extenders = append(extenders, extender)
			} else {
				ignorableExtenders = append(ignorableExtenders, extender)
			}
			for _, r := range policy.Extenders[ii].ManagedResources {
				if r.IgnoredByScheduler {
					ignoredExtendedResources.Insert(string(r.Name))
				}
			}
		}
		// place ignorable extenders to the tail of extenders
		extenders = append(extenders, ignorableExtenders...)
		predicates.RegisterPredicateMetadataProducerWithExtendedResourceOptions(ignoredExtendedResources)
	}
    ...
	return c.CreateFromKeys(predicateKeys, priorityKeys, extenders)
}

...
// Filters the nodes to find the ones that fit based on the given predicate functions
// Each node is passed through the predicate functions to determine if it is a fit
func (g *genericScheduler) findNodesThatFit(ctx context.Context, state *framework.CycleState, pod *v1.Pod) ([]*v1.Node, FailedPredicateMap, framework.NodeToStatusMap, error) {
	var filtered []*v1.Node
	failedPredicateMap := FailedPredicateMap{}
	filteredNodesStatuses := framework.NodeToStatusMap{}

	if len(g.predicates) == 0 && !g.framework.HasFilterPlugins() {
		filtered = g.nodeInfoSnapshot.ListNodes()
	} else {
		allNodes := len(g.nodeInfoSnapshot.NodeInfoList)
		numNodesToFind := g.numFeasibleNodesToFind(int32(allNodes))

		// Create filtered list with enough space to avoid growing it
		// and allow assigning.
		filtered = make([]*v1.Node, numNodesToFind)
		errCh := util.NewErrorChannel()
		var (
			predicateResultLock sync.Mutex
			filteredLen         int32
		)

		ctx, cancel := context.WithCancel(ctx)

		// We can use the same metadata producer for all nodes.
		meta := g.predicateMetaProducer(pod, g.nodeInfoSnapshot)
		state.Write(migration.PredicatesStateKey, &migration.PredicatesStateData{Reference: meta})

		checkNode := func(i int) {
			// We check the nodes starting from where we left off in the previous scheduling cycle,
			// this is to make sure all nodes have the same chance of being examined across pods.
			nodeInfo := g.nodeInfoSnapshot.NodeInfoList[(g.nextStartNodeIndex+i)%allNodes]
			fits, failedPredicates, status, err := g.podFitsOnNode(
				ctx,
				state,
				pod,
				meta,
				nodeInfo,
				g.alwaysCheckAllPredicates,
			)
			if err != nil {
				errCh.SendErrorWithCancel(err, cancel)
				return
			}
			if fits {
				length := atomic.AddInt32(&filteredLen, 1)
				if length > numNodesToFind {
					cancel()
					atomic.AddInt32(&filteredLen, -1)
				} else {
					filtered[length-1] = nodeInfo.Node()
				}
			} else {
				predicateResultLock.Lock()
				if !status.IsSuccess() {
					filteredNodesStatuses[nodeInfo.Node().Name] = status
				}
				if len(failedPredicates) != 0 {
					failedPredicateMap[nodeInfo.Node().Name] = failedPredicates
				}
				predicateResultLock.Unlock()
			}
		}

		// Stops searching for more nodes once the configured number of feasible nodes
		// are found.
		workqueue.ParallelizeUntil(ctx, 16, allNodes, checkNode)
		processedNodes := int(filteredLen) + len(filteredNodesStatuses) + len(failedPredicateMap)
		g.nextStartNodeIndex = (g.nextStartNodeIndex + processedNodes) % allNodes

		filtered = filtered[:filteredLen]
		if err := errCh.ReceiveError(); err != nil {
			return []*v1.Node{}, FailedPredicateMap{}, framework.NodeToStatusMap{}, err
		}
	}

	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.nodeInfoSnapshot.NodeInfoMap)
			if err != nil {
				if extender.IsIgnorable() {
					klog.Warningf("Skipping extender %v as it returned error %v and has ignorable flag set",
						extender, err)
					continue
				}

				return []*v1.Node{}, FailedPredicateMap{}, framework.NodeToStatusMap{}, 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, filteredNodesStatuses, nil
}

...
// SchedulerExtender is an interface for external processes to influence scheduling
// decisions made by Kubernetes. This is typically needed for resources not directly
// managed by Kubernetes.
type SchedulerExtender interface {
	// Name returns a unique name that identifies the extender.
	Name() string

	// Filter based on extender-implemented predicate functions. The filtered list is
	// expected to be a subset of the supplied list. failedNodesMap optionally contains
	// the list of failed nodes and failure reasons.
	Filter(pod *v1.Pod,
		nodes []*v1.Node, nodeNameToInfo map[string]*schedulernodeinfo.NodeInfo,
	) (filteredNodes []*v1.Node, failedNodesMap extenderv1.FailedNodesMap, err error)

	// Prioritize based on extender-implemented priority functions. The returned scores & weight
	// are used to compute the weighted score for an extender. The weighted scores are added to
	// the scores computed by Kubernetes scheduler. The total scores are used to do the host selection.
	Prioritize(pod *v1.Pod, nodes []*v1.Node) (hostPriorities *extenderv1.HostPriorityList, weight int64, err error)

	// Bind delegates the action of binding a pod to a node to the extender.
	Bind(binding *v1.Binding) error

	// IsBinder returns whether this extender is configured for the Bind method.
	IsBinder() bool

	// IsInterested returns true if at least one extended resource requested by
	// this pod is managed by this extender.
	IsInterested(pod *v1.Pod) bool

	// ProcessPreemption returns nodes with their victim pods processed by extender based on
	// given:
	//   1. Pod to schedule
	//   2. Candidate nodes and victim pods (nodeToVictims) generated by previous scheduling process.
	//   3. nodeNameToInfo to restore v1.Node from node name if extender cache is enabled.
	// The possible changes made by extender may include:
	//   1. Subset of given candidate nodes after preemption phase of extender.
	//   2. A different set of victim pod for every given candidate node after preemption phase of extender.
	ProcessPreemption(
		pod *v1.Pod,
		nodeToVictims map[*v1.Node]*extenderv1.Victims,
		nodeNameToInfo map[string]*schedulernodeinfo.NodeInfo,
	) (map[*v1.Node]*extenderv1.Victims, error)

	// SupportsPreemption returns if the scheduler extender support preemption or not.
	SupportsPreemption() bool

	// IsIgnorable returns true indicates scheduling should not fail when this extender
	// is unavailable. This gives scheduler ability to fail fast and tolerate non-critical extenders as well.
	IsIgnorable() bool
}

...
// k8s.io/kubernetes/pkg/scheduler/core/extender.go
// Filter based on extender implemented predicate functions. The filtered list is
// expected to be a subset of the supplied list; otherwise the function returns an error.
// failedNodesMap optionally contains the list of failed nodes and failure reasons.
func (h *HTTPExtender) Filter(
	pod *v1.Pod,
	nodes []*v1.Node, nodeNameToInfo map[string]*schedulernodeinfo.NodeInfo,
) ([]*v1.Node, extenderv1.FailedNodesMap, error) {
	var (
		result     extenderv1.ExtenderFilterResult
		nodeList   *v1.NodeList
		nodeNames  *[]string
		nodeResult []*v1.Node
		args       *extenderv1.ExtenderArgs
	)

	if h.filterVerb == "" {
		return nodes, extenderv1.FailedNodesMap{}, nil
	}

	if h.nodeCacheCapable {
		nodeNameSlice := make([]string, 0, len(nodes))
		for _, node := range nodes {
			nodeNameSlice = append(nodeNameSlice, node.Name)
		}
		nodeNames = &nodeNameSlice
	} else {
		nodeList = &v1.NodeList{}
		for _, node := range nodes {
			nodeList.Items = append(nodeList.Items, *node)
		}
	}

	args = &extenderv1.ExtenderArgs{
		Pod:       pod,
		Nodes:     nodeList,
		NodeNames: nodeNames,
	}

	if err := h.send(h.filterVerb, args, &result); err != nil {
		return nil, nil, err
	}
	if result.Error != "" {
		return nil, nil, fmt.Errorf(result.Error)
	}

	if h.nodeCacheCapable && result.NodeNames != nil {
		nodeResult = make([]*v1.Node, len(*result.NodeNames))
		for i, nodeName := range *result.NodeNames {
			if node, ok := nodeNameToInfo[nodeName]; ok {
				nodeResult[i] = node.Node()
			} else {
				return nil, nil, fmt.Errorf(
					"extender %q claims a filtered node %q which is not found in nodeNameToInfo map",
					h.extenderURL, nodeName)
			}
		}
	} else if result.Nodes != nil {
		nodeResult = make([]*v1.Node, len(result.Nodes.Items))
		for i := range result.Nodes.Items {
			nodeResult[i] = &result.Nodes.Items[i]
		}
	}

	return nodeResult, result.FailedNodes, nil
}

...
// Helper function to send messages to the extender
func (h *HTTPExtender) send(action string, args interface{}, result interface{}) error {
	out, err := json.Marshal(args)
	if err != nil {
		return err
	}

	url := strings.TrimRight(h.extenderURL, "/") + "/" + action

	req, err := http.NewRequest("POST", url, bytes.NewReader(out))
	if err != nil {
		return err
	}

	req.Header.Set("Content-Type", "application/json")

	resp, err := h.client.Do(req)
	if err != nil {
		return err
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("Failed %v with extender at URL %v, code %v", action, url, resp.StatusCode)
	}

	return json.NewDecoder(resp.Body).Decode(result)
}

// ExtenderFilterResult represents the results of a filter call to an extender
type ExtenderFilterResult struct {
	// Filtered set of nodes where the pod can be scheduled; to be populated
	// only if ExtenderConfig.NodeCacheCapable == false
	Nodes *v1.NodeList
	// Filtered set of nodes where the pod can be scheduled; to be populated
	// only if ExtenderConfig.NodeCacheCapable == true
	NodeNames *[]string
	// Filtered out nodes where the pod can't be scheduled and the failure messages
	FailedNodes FailedNodesMap
	// Error message indicating failure
	Error string
}

// ExtenderArgs represents the arguments needed by the extender to filter/prioritize
// nodes for a pod.
type ExtenderArgs struct {
	// Pod being scheduled
	Pod *v1.Pod
	// List of candidate nodes where the pod can be scheduled; to be populated
	// only if ExtenderConfig.NodeCacheCapable == false
	Nodes *v1.NodeList
	// List of candidate node names where the pod can be scheduled; to be
	// populated only if ExtenderConfig.NodeCacheCapable == true
	NodeNames *[]string
}

// prioritizeNodes prioritizes the nodes by running the individual priority functions in parallel.
// Each priority function is expected to set a score of 0-10
// 0 is the lowest priority score (least preferred node) and 10 is the highest
// Each priority function can also have its own weight
// The node scores returned by the priority function are multiplied by the weights to get weighted scores
// All scores are finally combined (added) to get the total weighted scores of all nodes
func (g *genericScheduler) prioritizeNodes(
	ctx context.Context,
	state *framework.CycleState,
	pod *v1.Pod,
	meta interface{},
	nodes []*v1.Node,
) (framework.NodeScoreList, error) {
	// If no priority configs are provided, then all nodes will have a score of one.
	// This is required to generate the priority list in the required format
	if len(g.prioritizers) == 0 && len(g.extenders) == 0 && !g.framework.HasScorePlugins() {
		result := make(framework.NodeScoreList, 0, len(nodes))
		for i := range nodes {
			result = append(result, framework.NodeScore{
				Name:  nodes[i].Name,
				Score: 1,
			})
		}
		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([]framework.NodeScoreList, len(g.prioritizers))

	for i := range g.prioritizers {
		results[i] = make(framework.NodeScoreList, len(nodes))
	}

	workqueue.ParallelizeUntil(context.TODO(), 16, len(nodes), func(index int) {
		nodeInfo := g.nodeInfoSnapshot.NodeInfoMap[nodes[index].Name]
		for i := range g.prioritizers {
			var err error
			results[i][index], err = g.prioritizers[i].Map(pod, meta, nodeInfo)
			if err != nil {
				appendError(err)
				results[i][index].Name = nodes[index].Name
			}
		}
	})

	for i := range g.prioritizers {
		if g.prioritizers[i].Reduce == nil {
			continue
		}
		wg.Add(1)
		go func(index int) {
			metrics.SchedulerGoroutines.WithLabelValues("prioritizing_mapreduce").Inc()
			defer func() {
				metrics.SchedulerGoroutines.WithLabelValues("prioritizing_mapreduce").Dec()
				wg.Done()
			}()
			if err := g.prioritizers[index].Reduce(pod, meta, g.nodeInfoSnapshot, 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.Name, g.prioritizers[index].Name, hostPriority.Score)
				}
			}
		}(i)
	}
	// Wait for all computations to be finished.
	wg.Wait()
	if len(errs) != 0 {
		return framework.NodeScoreList{}, errors.NewAggregate(errs)
	}

	// Run the Score plugins.
	state.Write(migration.PrioritiesStateKey, &migration.PrioritiesStateData{Reference: meta})
	scoresMap, scoreStatus := g.framework.RunScorePlugins(ctx, state, pod, nodes)
	if !scoreStatus.IsSuccess() {
		return framework.NodeScoreList{}, scoreStatus.AsError()
	}

	// Summarize all scores.
	result := make(framework.NodeScoreList, 0, len(nodes))

	for i := range nodes {
		result = append(result, framework.NodeScore{Name: nodes[i].Name, Score: 0})
		for j := range g.prioritizers {
			result[i].Score += results[j][i].Score * g.prioritizers[j].Weight
		}

		for j := range scoresMap {
			result[i].Score += scoresMap[j][i].Score
		}
	}

	if len(g.extenders) != 0 && nodes != nil {
		combinedScores := make(map[string]int64, len(g.nodeInfoSnapshot.NodeInfoList))
		for i := range g.extenders {
			if !g.extenders[i].IsInterested(pod) {
				continue
			}
			wg.Add(1)
			go func(extIndex int) {
				metrics.SchedulerGoroutines.WithLabelValues("prioritizing_extender").Inc()
				defer func() {
					metrics.SchedulerGoroutines.WithLabelValues("prioritizing_extender").Dec()
					wg.Done()
				}()
				prioritizedList, weight, err := g.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, g.extenders[extIndex].Name(), score)
					}
					combinedScores[host] += score * weight
				}
				mu.Unlock()
			}(i)
		}
		// wait for all go routines to finish
		wg.Wait()
		for i := range result {
			// MaxExtenderPriority may diverge from the max priority used in the scheduler and defined by MaxNodeScore,
			// therefore we need to scale the score returned by extenders to the score range used by the scheduler.
			result[i].Score += combinedScores[result[i].Name] * (framework.MaxNodeScore / extenderv1.MaxExtenderPriority)
		}
	}

	if klog.V(10) {
		for i := range result {
			klog.Infof("Host %s => Score %d", result[i].Name, result[i].Score)
		}
	}
	return result, nil
}

...
// Prioritize based on extender implemented priority functions. Weight*priority is added
// up for each such priority function. The returned score is added to the score computed
// by Kubernetes scheduler. The total score is used to do the host selection.
func (h *HTTPExtender) Prioritize(pod *v1.Pod, nodes []*v1.Node) (*extenderv1.HostPriorityList, int64, error) {
	var (
		result    extenderv1.HostPriorityList
		nodeList  *v1.NodeList
		nodeNames *[]string
		args      *extenderv1.ExtenderArgs
	)

	if h.prioritizeVerb == "" {
		result := extenderv1.HostPriorityList{}
		for _, node := range nodes {
			result = append(result, extenderv1.HostPriority{Host: node.Name, Score: 0})
		}
		return &result, 0, nil
	}

	if h.nodeCacheCapable {
		nodeNameSlice := make([]string, 0, len(nodes))
		for _, node := range nodes {
			nodeNameSlice = append(nodeNameSlice, node.Name)
		}
		nodeNames = &nodeNameSlice
	} else {
		nodeList = &v1.NodeList{}
		for _, node := range nodes {
			nodeList.Items = append(nodeList.Items, *node)
		}
	}

	args = &extenderv1.ExtenderArgs{
		Pod:       pod,
		Nodes:     nodeList,
		NodeNames: nodeNames,
	}

	if err := h.send(h.prioritizeVerb, args, &result); err != nil {
		return nil, 0, err
	}
	return &result, h.weight, nil
}

// HostPriority represents the priority of scheduling to a particular host, higher priority is better.
type HostPriority struct {
	// Name of the host
	Host string
	// Score associated with the host
	Score int64
}

// HostPriorityList declares a []HostPriority type.
type HostPriorityList []HostPriority

// MaxExtenderPriority may diverge from the max priority used in the scheduler and defined by MaxNodeScore,
// therefore we need to scale the score returned by extenders to the score range used by the scheduler.
result[i].Score += combinedScores[result[i].Name] * (framework.MaxNodeScore / extenderv1.MaxExtenderPriority)

...
const (
	// MaxNodeScore is the maximum score a Score plugin is expected to return.
	MaxNodeScore int64 = 100

	// MinNodeScore is the minimum score a Score plugin is expected to return.
	MinNodeScore int64 = 0

	// MaxTotalScore is the maximum total score.
	MaxTotalScore int64 = math.MaxInt64
)

...
const (
	// MinExtenderPriority defines the min priority value for extender.
	MinExtenderPriority int64 = 0

	// MaxExtenderPriority defines the max priority value for extender.
	MaxExtenderPriority int64 = 10
)

// PluginFactory is a function that builds a plugin.
type PluginFactory = func(configuration *runtime.Unknown, f FrameworkHandle) (Plugin, error)

// Registry is a collection of all available plugins. The framework uses a
// registry to enable and initialize configured plugins.
// All plugins must be in the registry before initializing the framework.
type Registry map[string]PluginFactory

// Register adds a new plugin to the registry. If a plugin with the same name
// exists, it returns an error.
func (r Registry) Register(name string, factory PluginFactory) error {
	if _, ok := r[name]; ok {
		return fmt.Errorf("a plugin named %v already exists", name)
	}
	r[name] = factory
	return nil
}

// WithPlugin creates an Option based on plugin name and factory.
func WithPlugin(name string, factory framework.PluginFactory) Option {
	return func(registry framework.Registry) error {
		return registry.Register(name, factory)
	}
}

func main() {
	rand.Seed(time.Now().UnixNano())
	// Register custom plugins to the scheduler framework.
	// Later they can consist of scheduler profile(s) and hence
	// used by various kinds of workloads.
	command := app.NewSchedulerCommand(
		app.WithPlugin(coscheduling.Name, coscheduling.New),
		app.WithPlugin(qos.Name, qos.New),
	)
	if err := command.Execute(); err != nil {
		os.Exit(1)
	}
}

// New initializes a new plugin and returns it.
func New(_ *runtime.Unknown, handle framework.FrameworkHandle) (framework.Plugin, error) {
	podLister := handle.SharedInformerFactory().Core().V1().Pods().Lister()
	return &Coscheduling{frameworkHandle: handle,
		podLister: podLister,
	}, nil
}

// FrameworkHandle provides data and some tools that plugins can use. It is
// passed to the plugin factories at the time of plugin initialization. Plugins
// must store and use this handle to call framework functions.
type FrameworkHandle interface {
	// SnapshotSharedLister returns listers from the latest NodeInfo Snapshot. The snapshot
	// is taken at the beginning of a scheduling cycle and remains unchanged until
	// a pod finishes "Reserve" point. There is no guarantee that the information
	// remains unchanged in the binding phase of scheduling, so plugins in the binding
	// cycle(permit/pre-bind/bind/post-bind/un-reserve plugin) should not use it,
	// otherwise a concurrent read/write error might occur, they should use scheduler
	// cache instead.
	SnapshotSharedLister() schedulerlisters.SharedLister

	// IterateOverWaitingPods acquires a read lock and iterates over the WaitingPods map.
	IterateOverWaitingPods(callback func(WaitingPod))

	// GetWaitingPod returns a waiting pod given its UID.
	GetWaitingPod(uid types.UID) WaitingPod

	// RejectWaitingPod rejects a waiting pod given its UID.
	RejectWaitingPod(uid types.UID)

	// ClientSet returns a kubernetes clientSet.
	ClientSet() clientset.Interface

	SharedInformerFactory() informers.SharedInformerFactory
}

// NewFramework initializes plugins given the configuration and the registry.
func NewFramework(r Registry, plugins *config.Plugins, args []config.PluginConfig, opts ...Option) (Framework, error) {
	options := defaultFrameworkOptions
	for _, opt := range opts {
		opt(&options)
	}

	f := &framework{
		registry:              r,
		snapshotSharedLister:  options.snapshotSharedLister,
		pluginNameToWeightMap: make(map[string]int),
		waitingPods:           newWaitingPodsMap(),
		clientSet:             options.clientSet,
		informerFactory:       options.informerFactory,
		metricsRecorder:       options.metricsRecorder,
	}
	if plugins == nil {
		return f, nil
	}

	// get needed plugins from config
	pg := f.pluginsNeeded(plugins)
	if len(pg) == 0 {
		return f, nil
	}

	pluginConfig := make(map[string]*runtime.Unknown, 0)
	for i := range args {
		pluginConfig[args[i].Name] = &args[i].Args
	}

	pluginsMap := make(map[string]Plugin)
	for name, factory := range r {
		// initialize only needed plugins.
		if _, ok := pg[name]; !ok {
			continue
		}

		p, err := factory(pluginConfig[name], f)
		if err != nil {
			return nil, fmt.Errorf("error initializing plugin %q: %v", name, err)
		}
		pluginsMap[name] = p

		// a weight of zero is not permitted, plugins can be disabled explicitly
		// when configured.
		f.pluginNameToWeightMap[name] = int(pg[name].Weight)
		if f.pluginNameToWeightMap[name] == 0 {
			f.pluginNameToWeightMap[name] = 1
		}
	}

	for _, e := range f.getExtensionPoints(plugins) {
		if err := updatePluginList(e.slicePtr, e.plugins, pluginsMap); err != nil {
			return nil, err
		}
	}

	// Verifying the score weights again since Plugin.Name() could return a different
	// value from the one used in the configuration.
	for _, scorePlugin := range f.scorePlugins {
		if f.pluginNameToWeightMap[scorePlugin.Name()] == 0 {
			return nil, fmt.Errorf("score plugin %q is not configured with weight", scorePlugin.Name())
		}
	}

	if len(f.queueSortPlugins) > 1 {
		return nil, fmt.Errorf("only one queue sort plugin can be enabled")
	}

	return f, nil
}

func (f *framework) getExtensionPoints(plugins *config.Plugins) []extensionPoint {
	return []extensionPoint{
		{plugins.PreFilter, &f.preFilterPlugins},
		{plugins.Filter, &f.filterPlugins},
		{plugins.Reserve, &f.reservePlugins},
		{plugins.PostFilter, &f.postFilterPlugins},
		{plugins.Score, &f.scorePlugins},
		{plugins.PreBind, &f.preBindPlugins},
		{plugins.Bind, &f.bindPlugins},
		{plugins.PostBind, &f.postBindPlugins},
		{plugins.Unreserve, &f.unreservePlugins},
		{plugins.Permit, &f.permitPlugins},
		{plugins.QueueSort, &f.queueSortPlugins},
	}
}

func updatePluginList(pluginList interface{}, pluginSet *config.PluginSet, pluginsMap map[string]Plugin) error {
	if pluginSet == nil {
		return nil
	}

	plugins := reflect.ValueOf(pluginList).Elem()
	pluginType := plugins.Type().Elem()
	set := sets.NewString()
	for _, ep := range pluginSet.Enabled {
		pg, ok := pluginsMap[ep.Name]
		if !ok {
			return fmt.Errorf("%s %q does not exist", pluginType.Name(), ep.Name)
		}

		if !reflect.TypeOf(pg).Implements(pluginType) {
			return fmt.Errorf("plugin %q does not extend %s plugin", ep.Name, pluginType.Name())
		}

		if set.Has(ep.Name) {
			return fmt.Errorf("plugin %q already registered as %q", ep.Name, pluginType.Name())
		}

		set.Insert(ep.Name)

		newPlugins := reflect.Append(plugins, reflect.ValueOf(pg))
		plugins.Set(newPlugins)
	}
	return nil
}

// framework is the component responsible for initializing and running scheduler
// plugins.
type framework struct {
	registry              Registry
	snapshotSharedLister  schedulerlisters.SharedLister
	waitingPods           *waitingPodsMap
	pluginNameToWeightMap map[string]int
	queueSortPlugins      []QueueSortPlugin
	preFilterPlugins      []PreFilterPlugin
	filterPlugins         []FilterPlugin
	postFilterPlugins     []PostFilterPlugin
	scorePlugins          []ScorePlugin
	reservePlugins        []ReservePlugin
	preBindPlugins        []PreBindPlugin
	bindPlugins           []BindPlugin
	postBindPlugins       []PostBindPlugin
	unreservePlugins      []UnreservePlugin
	permitPlugins         []PermitPlugin

	clientSet       clientset.Interface
	informerFactory informers.SharedInformerFactory

	metricsRecorder *metricsRecorder
}

// Plugin is the parent type for all the scheduling framework plugins.
type Plugin interface {
	Name() string
}

// FilterPlugin is an interface for Filter plugins. These plugins are called at the
// filter extension point for filtering out hosts that cannot run a pod.
// This concept used to be called 'predicate' in the original scheduler.
// These plugins should return "Success", "Unschedulable" or "Error" in Status.code.
// However, the scheduler accepts other valid codes as well.
// Anything other than "Success" will lead to exclusion of the given host from
// running the pod.
type FilterPlugin interface {
	Plugin
	// Filter is called by the scheduling framework.
	// All FilterPlugins should return "Success" to declare that
	// the given node fits the pod. If Filter doesn't return "Success",
	// please refer scheduler/algorithm/predicates/error.go
	// to set error message.
	// For the node being evaluated, Filter plugins should look at the passed
	// nodeInfo reference for this particular node's information (e.g., pods
	// considered to be running on the node) instead of looking it up in the
	// NodeInfoSnapshot because we don't guarantee that they will be the same.
	// For example, during preemption, we may pass a copy of the original
	// nodeInfo object that has some pods removed from it to evaluate the
	// possibility of preempting them to schedule the target pod.
	Filter(ctx context.Context, state *CycleState, pod *v1.Pod, nodeInfo *schedulernodeinfo.NodeInfo) *Status
}

...
// ScorePlugin is an interface that must be implemented by "score" plugins to rank
// nodes that passed the filtering phase.
type ScorePlugin interface {
	Plugin
	// Score is called on each filtered node. It must return success and an integer
	// indicating the rank of the node. All scoring plugins must return success or
	// the pod will be rejected.
	Score(ctx context.Context, state *CycleState, p *v1.Pod, nodeName string) (int64, *Status)

	// ScoreExtensions returns a ScoreExtensions interface if it implements one, or nil if does not.
	ScoreExtensions() ScoreExtensions
}

// KubeSchedulerConfiguration configures a scheduler
type KubeSchedulerConfiguration struct {
    ...
	// Plugins specify the set of plugins that should be enabled or disabled. Enabled plugins are the
	// ones that should be enabled in addition to the default plugins. Disabled plugins are any of the
	// default plugins that should be disabled.
	// When no enabled or disabled plugin is specified for an extension point, default plugins for
	// that extension point will be used if there is any.
	Plugins *Plugins

	// PluginConfig is an optional set of custom plugin arguments for each plugin.
	// Omitting config args for a plugin is equivalent to using the default config for that plugin.
	PluginConfig []PluginConfig
}

// Plugins include multiple extension points. When specified, the list of plugins for
// a particular extension point are the only ones enabled. If an extension point is
// omitted from the config, then the default set of plugins is used for that extension point.
// Enabled plugins are called in the order specified here, after default plugins. If they need to
// be invoked before default plugins, default plugins must be disabled and re-enabled here in desired order.
type Plugins struct {
	// QueueSort is a list of plugins that should be invoked when sorting pods in the scheduling queue.
	QueueSort *PluginSet

	// PreFilter is a list of plugins that should be invoked at "PreFilter" extension point of the scheduling framework.
	PreFilter *PluginSet

	// Filter is a list of plugins that should be invoked when filtering out nodes that cannot run the Pod.
	Filter *PluginSet

	// PostFilter is a list of plugins that are invoked after filtering out infeasible nodes.
	PostFilter *PluginSet

	// Score is a list of plugins that should be invoked when ranking nodes that have passed the filtering phase.
	Score *PluginSet

	// Reserve is a list of plugins invoked when reserving a node to run the pod.
	Reserve *PluginSet

	// Permit is a list of plugins that control binding of a Pod. These plugins can prevent or delay binding of a Pod.
	Permit *PluginSet

	// PreBind is a list of plugins that should be invoked before a pod is bound.
	PreBind *PluginSet

	// Bind is a list of plugins that should be invoked at "Bind" extension point of the scheduling framework.
	// The scheduler call these plugins in order. Scheduler skips the rest of these plugins as soon as one returns success.
	Bind *PluginSet

	// PostBind is a list of plugins that should be invoked after a pod is successfully bound.
	PostBind *PluginSet

	// Unreserve is a list of plugins invoked when a pod that was previously reserved is rejected in a later phase.
	Unreserve *PluginSet
}

// PluginSet specifies enabled and disabled plugins for an extension point.
// If an array is empty, missing, or nil, default plugins at that extension point will be used.
type PluginSet struct {
	// Enabled specifies plugins that should be enabled in addition to default plugins.
	// These are called after default plugins and in the same order specified here.
	Enabled []Plugin
	// Disabled specifies default plugins that should be disabled.
	// When all default plugins need to be disabled, an array containing only one "*" should be provided.
	Disabled []Plugin
}

// Plugin specifies a plugin name and its weight when applicable. Weight is used only for Score plugins.
type Plugin struct {
	// Name defines the name of plugin
	Name string
	// Weight defines the weight of plugin, only used for Score plugins.
	Weight int32
}

// PluginConfig specifies arguments that should be passed to a plugin at the time of initialization.
// A plugin that is invoked at multiple extension points is initialized once. Args can have arbitrary structure.
// It is up to the plugin to process these Args.
type PluginConfig struct {
	// Name defines the name of plugin being configured
	Name string
	// Args defines the arguments passed to the plugins at the time of initialization. Args can have arbitrary structure.
	Args runtime.Unknown
}