Merge pull request #77828 from Huang-Wei/eps-pred-core

Even Pods Spread - 3. Predicates Core

pkg/scheduler/algorithm/predicates/error.go

@@ -75,6 +75,8 @@ var (
 	ErrVolumeNodeConflict = newPredicateFailureError("VolumeNodeAffinityConflict", "node(s) had volume node affinity conflict")
 	// ErrVolumeBindConflict is used for VolumeBindingNoMatch predicate error.
 	ErrVolumeBindConflict = newPredicateFailureError("VolumeBindingNoMatch", "node(s) didn't find available persistent volumes to bind")
+	// ErrTopologySpreadConstraintsNotMatch is used for EvenPodsSpread predicate error.
+	ErrTopologySpreadConstraintsNotMatch = newPredicateFailureError("EvenPodsSpreadNotMatch", "node(s) didn't match pod topology spread constraints")
 	// ErrFakePredicate is used for test only. The fake predicates returning false also returns error
 	// as ErrFakePredicate.
 	ErrFakePredicate = newPredicateFailureError("FakePredicateError", "Nodes failed the fake predicate")

pkg/scheduler/algorithm/predicates/predicates.go

@@ -106,6 +106,8 @@ const (
 	CheckNodeDiskPressurePred = "CheckNodeDiskPressure"
 	// CheckNodePIDPressurePred defines the name of predicate CheckNodePIDPressure.
 	CheckNodePIDPressurePred = "CheckNodePIDPressure"
+	// EvenPodsSpreadPred defines the name of predicate EvenPodsSpread
+	EvenPodsSpreadPred = "EvenPodsSpread"
 
 	// DefaultMaxGCEPDVolumes defines the maximum number of PD Volumes for GCE
 	// GCE instances can have up to 16 PD volumes attached.
@@ -148,7 +150,7 @@ var (
 		PodToleratesNodeTaintsPred, PodToleratesNodeNoExecuteTaintsPred, CheckNodeLabelPresencePred,
 		CheckServiceAffinityPred, MaxEBSVolumeCountPred, MaxGCEPDVolumeCountPred, MaxCSIVolumeCountPred,
 		MaxAzureDiskVolumeCountPred, MaxCinderVolumeCountPred, CheckVolumeBindingPred, NoVolumeZoneConflictPred,
-		CheckNodeMemoryPressurePred, CheckNodePIDPressurePred, CheckNodeDiskPressurePred, MatchInterPodAffinityPred}
+		CheckNodeMemoryPressurePred, CheckNodePIDPressurePred, CheckNodeDiskPressurePred, EvenPodsSpreadPred, MatchInterPodAffinityPred}
 )
 
 // FitPredicate is a function that indicates if a pod fits into an existing node.
@@ -1712,3 +1714,68 @@ func (c *VolumeBindingChecker) predicate(pod *v1.Pod, meta PredicateMetadata, no
 	klog.V(5).Infof("All PVCs found matches for pod %v/%v, node %q", pod.Namespace, pod.Name, node.Name)
 	return true, nil, nil
 }
+
+// EvenPodsSpreadPredicate checks if a pod can be scheduled on a node which satisfies
+// its topologySpreadConstraints.
+func EvenPodsSpreadPredicate(pod *v1.Pod, meta PredicateMetadata, nodeInfo *schedulernodeinfo.NodeInfo) (bool, []PredicateFailureReason, error) {
+	node := nodeInfo.Node()
+	if node == nil {
+		return false, nil, fmt.Errorf("node not found")
+	}
+
+	constraints := getHardTopologySpreadConstraints(pod)
+	if len(constraints) == 0 {
+		return true, nil, nil
+	}
+
+	var topologyPairsPodSpreadMap *topologyPairsPodSpreadMap
+	if predicateMeta, ok := meta.(*predicateMetadata); ok {
+		topologyPairsPodSpreadMap = predicateMeta.topologyPairsPodSpreadMap
+	} else { // We don't have precomputed metadata. We have to follow a slow path to check spread constraints.
+		// TODO(Huang-Wei): get it implemented
+		return false, nil, errors.New("metadata not pre-computed for EvenPodsSpreadPredicate")
+	}
+
+	if topologyPairsPodSpreadMap == nil || len(topologyPairsPodSpreadMap.topologyKeyToMinPodsMap) == 0 {
+		return true, nil, nil
+	}
+
+	podLabelSet := labels.Set(pod.Labels)
+	for _, constraint := range constraints {
+		tpKey := constraint.TopologyKey
+		tpVal, ok := node.Labels[constraint.TopologyKey]
+		if !ok {
+			klog.V(5).Infof("node '%s' doesn't have required label '%s'", node.Name, tpKey)
+			return false, []PredicateFailureReason{ErrTopologySpreadConstraintsNotMatch}, nil
+		}
+
+		selfMatch, err := podMatchesSpreadConstraint(podLabelSet, constraint)
+		if err != nil {
+			return false, nil, err
+		}
+		selfMatchNum := 0
+		if selfMatch {
+			selfMatchNum = 1
+		}
+
+		pair := topologyPair{key: tpKey, value: tpVal}
+		minMatchNum, ok := topologyPairsPodSpreadMap.topologyKeyToMinPodsMap[tpKey]
+		if !ok {
+			// error which should not happen
+			klog.Errorf("internal error: get minMatchNum from key %q of %#v", tpKey, topologyPairsPodSpreadMap.topologyKeyToMinPodsMap)
+			continue
+		}
+		// judging criteria:
+		// 'existing matching num' + 'if self-match (1 or 0)' - 'global min matching num' <= 'maxSkew'
+		matchNum := len(topologyPairsPodSpreadMap.topologyPairToPods[pair])
+
+		// cast to int to avoid potential overflow.
+		skew := matchNum + selfMatchNum - int(minMatchNum)
+		if skew > int(constraint.MaxSkew) {
+			klog.V(5).Infof("node '%s' failed spreadConstraint[%s]: matchNum(%d) + selfMatchNum(%d) - minMatchNum(%d) > maxSkew(%d)", node.Name, tpKey, matchNum, selfMatchNum, minMatchNum, constraint.MaxSkew)
+			return false, []PredicateFailureReason{ErrTopologySpreadConstraintsNotMatch}, nil
+		}
+	}
+
+	return true, nil, nil
+}

pkg/scheduler/algorithm/predicates/predicates_test.go

@@ -35,7 +35,7 @@ import (
 	"k8s.io/kubernetes/pkg/features"
 	schedulerapi "k8s.io/kubernetes/pkg/scheduler/api"
 	schedulernodeinfo "k8s.io/kubernetes/pkg/scheduler/nodeinfo"
-	schedulertesting "k8s.io/kubernetes/pkg/scheduler/testing"
+	st "k8s.io/kubernetes/pkg/scheduler/testing"
 )
 
 var (
@@ -95,7 +95,7 @@ func newResourceOverheadPod(pod *v1.Pod, overhead v1.ResourceList) *v1.Pod {
 }
 
 func GetPredicateMetadata(p *v1.Pod, nodeInfo map[string]*schedulernodeinfo.NodeInfo) PredicateMetadata {
-	pm := PredicateMetadataFactory{schedulertesting.FakePodLister{p}}
+	pm := PredicateMetadataFactory{st.FakePodLister{p}}
 	return pm.GetMetadata(p, nodeInfo)
 }
 
@@ -1863,7 +1863,7 @@ func TestServiceAffinity(t *testing.T) {
 				nodeInfo.SetNode(test.node)
 				nodeInfoMap := map[string]*schedulernodeinfo.NodeInfo{test.node.Name: nodeInfo}
 				// Reimplementing the logic that the scheduler implements: Any time it makes a predicate, it registers any precomputations.
-				predicate, precompute := NewServiceAffinityPredicate(schedulertesting.FakePodLister(test.pods), schedulertesting.FakeServiceLister(test.services), FakeNodeListInfo(nodes), test.labels)
+				predicate, precompute := NewServiceAffinityPredicate(st.FakePodLister(test.pods), st.FakeServiceLister(test.services), FakeNodeListInfo(nodes), test.labels)
 				// Register a precomputation or Rewrite the precomputation to a no-op, depending on the state we want to test.
 				RegisterPredicateMetadataProducer("ServiceAffinityMetaProducer", func(pm *predicateMetadata) {
 					if !skipPrecompute {
@@ -2937,7 +2937,7 @@ func TestInterPodAffinity(t *testing.T) {
 
 			fit := PodAffinityChecker{
 				info:      FakeNodeInfo(*node),
-				podLister: schedulertesting.FakePodLister(test.pods),
+				podLister: st.FakePodLister(test.pods),
 			}
 			nodeInfo := schedulernodeinfo.NewNodeInfo(podsOnNode...)
 			nodeInfo.SetNode(test.node)
@@ -4051,7 +4051,7 @@ func TestInterPodAffinityWithMultipleNodes(t *testing.T) {
 			for indexNode, node := range test.nodes {
 				testFit := PodAffinityChecker{
 					info:      nodeListInfo,
-					podLister: schedulertesting.FakePodLister(test.pods),
+					podLister: st.FakePodLister(test.pods),
 				}
 
 				var meta PredicateMetadata
@@ -5039,3 +5039,445 @@ func TestCheckNodeUnschedulablePredicate(t *testing.T) {
 		}
 	}
 }
+
+func TestEvenPodsSpreadPredicate_SingleConstraint(t *testing.T) {
+	tests := []struct {
+		name         string
+		pod          *v1.Pod
+		nodes        []*v1.Node
+		existingPods []*v1.Pod
+		fits         map[string]bool
+	}{
+		{
+			name: "no existing pods",
+			pod: st.MakePod().Name("p").Label("foo", "").SpreadConstraint(
+				1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj(),
+			).Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": true,
+				"node-b": true,
+				"node-x": true,
+				"node-y": true,
+			},
+		},
+		{
+			name: "no existing pods, incoming pod doesn't match itself",
+			pod: st.MakePod().Name("p").Label("foo", "").SpreadConstraint(
+				1, "zone", hardSpread, st.MakeLabelSelector().Exists("bar").Obj(),
+			).Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": true,
+				"node-b": true,
+				"node-x": true,
+				"node-y": true,
+			},
+		},
+		{
+			name: "existing pods with mis-matched namespace doens't count",
+			pod: st.MakePod().Name("p").Label("foo", "").SpreadConstraint(
+				1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj(),
+			).Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Namespace("ns1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-b1").Namespace("ns2").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-x1").Node("node-x").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": true,
+				"node-b": true,
+				"node-x": false,
+				"node-y": false,
+			},
+		},
+		{
+			name: "pods spread across zones as 3/3, all nodes fit",
+			pod: st.MakePod().Name("p").Label("foo", "").SpreadConstraint(
+				1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj(),
+			).Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-b1").Node("node-b").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y2").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y3").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": true,
+				"node-b": true,
+				"node-x": true,
+				"node-y": true,
+			},
+		},
+		{
+			// TODO(Huang-Wei): maybe document this to remind users that typos on node labels
+			// can cause unexpected behavior
+			name: "pods spread across zones as 1/2 due to absence of label 'zone' on node-b",
+			pod: st.MakePod().Name("p").Label("foo", "").SpreadConstraint(
+				1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj(),
+			).Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zon", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-b1").Node("node-b").Label("foo", "").Obj(),
+				st.MakePod().Name("p-x1").Node("node-x").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": true,
+				"node-b": false,
+				"node-x": false,
+				"node-y": false,
+			},
+		},
+		{
+			name: "pods spread across nodes as 2/1/0/3, only node-x fits",
+			pod: st.MakePod().Name("p").Label("foo", "").SpreadConstraint(
+				1, "node", hardSpread, st.MakeLabelSelector().Exists("foo").Obj(),
+			).Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-b1").Node("node-b").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y2").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y3").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": false,
+				"node-b": false,
+				"node-x": true,
+				"node-y": false,
+			},
+		},
+		{
+			name: "pods spread across nodes as 2/1/0/3, maxSkew is 2, node-b and node-x fit",
+			pod: st.MakePod().Name("p").Label("foo", "").SpreadConstraint(
+				2, "node", hardSpread, st.MakeLabelSelector().Exists("foo").Obj(),
+			).Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-b1").Node("node-b").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y2").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y3").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": false,
+				"node-b": true,
+				"node-x": true,
+				"node-y": false,
+			},
+		},
+		{
+			// not a desired case, but it can happen
+			// TODO(Huang-Wei): document this "pod-not-match-itself" case
+			// in this case, placement of the new pod doesn't change pod distribution of the cluster
+			// as the incoming pod doesn't have label "foo"
+			name: "pods spread across nodes as 2/1/0/3, but pod doesn't match itself",
+			pod: st.MakePod().Name("p").Label("bar", "").SpreadConstraint(
+				1, "node", hardSpread, st.MakeLabelSelector().Exists("foo").Obj(),
+			).Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-b1").Node("node-b").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y2").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y3").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": false,
+				"node-b": true,
+				"node-x": true,
+				"node-y": false,
+			},
+		},
+		{
+			// only node-a and node-y are considered, so pods spread as 2/~1~/~0~/3
+			// ps: '~num~' is a markdown symbol to denote a crossline through 'num'
+			// but in this unit test, we don't run NodeAffinityPredicate, so node-b and node-x are
+			// still expected to be fits;
+			// the fact that node-a fits can prove the underlying logic works
+			name: "incoming pod has nodeAffinity, pods spread as 2/~1~/~0~/3, hence node-a fits",
+			pod: st.MakePod().Name("p").Label("foo", "").
+				NodeAffinityIn("node", []string{"node-a", "node-y"}).
+				SpreadConstraint(1, "node", hardSpread, st.MakeLabelSelector().Exists("foo").Obj()).
+				Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-b1").Node("node-b").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y2").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y3").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": true,
+				"node-b": true, // in real case, it's false
+				"node-x": true, // in real case, it's false
+				"node-y": false,
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			nodeInfoMap := schedulernodeinfo.CreateNodeNameToInfoMap(tt.existingPods, tt.nodes)
+			meta := GetPredicateMetadata(tt.pod, nodeInfoMap)
+			for _, node := range tt.nodes {
+				fits, _, _ := EvenPodsSpreadPredicate(tt.pod, meta, nodeInfoMap[node.Name])
+				if fits != tt.fits[node.Name] {
+					t.Errorf("[%s]: expected %v got %v", node.Name, tt.fits[node.Name], fits)
+				}
+			}
+		})
+	}
+}
+
+func TestEvenPodsSpreadPredicate_MultipleConstraints(t *testing.T) {
+	tests := []struct {
+		name         string
+		pod          *v1.Pod
+		nodes        []*v1.Node
+		existingPods []*v1.Pod
+		fits         map[string]bool
+	}{
+		{
+			// 1. to fulfil "zone" constraint, incoming pod can be placed on any zone (hence any node)
+			// 2. to fulfil "node" constraint, incoming pod can be placed on node-x
+			// intersection of (1) and (2) returns node-x
+			name: "two constraints on zone and node, spreads = [3/3, 2/1/0/3]",
+			pod: st.MakePod().Name("p").Label("foo", "").
+				SpreadConstraint(1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj()).
+				SpreadConstraint(1, "node", hardSpread, st.MakeLabelSelector().Exists("foo").Obj()).
+				Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-b1").Node("node-b").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y2").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y3").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": false,
+				"node-b": false,
+				"node-x": true,
+				"node-y": false,
+			},
+		},
+		{
+			// 1. to fulfil "zone" constraint, incoming pod can be placed on zone1 (node-a or node-b)
+			// 2. to fulfil "node" constraint, incoming pod can be placed on node-x
+			// intersection of (1) and (2) returns no node
+			name: "two constraints on zone and node, spreads = [3/4, 2/1/0/4]",
+			pod: st.MakePod().Name("p").Label("foo", "").
+				SpreadConstraint(1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj()).
+				SpreadConstraint(1, "node", hardSpread, st.MakeLabelSelector().Exists("foo").Obj()).
+				Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-b1").Node("node-b").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y2").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y3").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y4").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": false,
+				"node-b": false,
+				"node-x": false,
+				"node-y": false,
+			},
+		},
+		{
+			// 1. to fulfil "zone" constraint, incoming pod can be placed on zone2 (node-x or node-y)
+			// 2. to fulfil "node" constraint, incoming pod can be placed on node-b or node-x
+			// intersection of (1) and (2) returns node-x
+			name: "constraints hold different labelSelectors, spreads = [1/0, 1/0/0/1]",
+			pod: st.MakePod().Name("p").Label("foo", "").Label("bar", "").
+				SpreadConstraint(1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj()).
+				SpreadConstraint(1, "node", hardSpread, st.MakeLabelSelector().Exists("bar").Obj()).
+				Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("bar", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": false,
+				"node-b": false,
+				"node-x": true,
+				"node-y": false,
+			},
+		},
+		{
+			// 1. to fulfil "zone" constraint, incoming pod can be placed on zone2 (node-x or node-y)
+			// 2. to fulfil "node" constraint, incoming pod can be placed on node-a or node-b
+			// intersection of (1) and (2) returns no node
+			name: "constraints hold different labelSelectors, spreads = [1/0, 0/0/1/1]",
+			pod: st.MakePod().Name("p").Label("foo", "").Label("bar", "").
+				SpreadConstraint(1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj()).
+				SpreadConstraint(1, "node", hardSpread, st.MakeLabelSelector().Exists("bar").Obj()).
+				Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-x1").Node("node-x").Label("bar", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("bar", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": false,
+				"node-b": false,
+				"node-x": false,
+				"node-y": false,
+			},
+		},
+		{
+			// 1. to fulfil "zone" constraint, incoming pod can be placed on zone1 (node-a or node-b)
+			// 2. to fulfil "node" constraint, incoming pod can be placed on node-b or node-x
+			// intersection of (1) and (2) returns node-b
+			name: "constraints hold different labelSelectors, spreads = [2/3, 1/0/0/1]",
+			pod: st.MakePod().Name("p").Label("foo", "").Label("bar", "").
+				SpreadConstraint(1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj()).
+				SpreadConstraint(1, "node", hardSpread, st.MakeLabelSelector().Exists("bar").Obj()).
+				Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-a2").Node("node-a").Label("foo", "").Label("bar", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("foo", "").Obj(),
+				st.MakePod().Name("p-y2").Node("node-y").Label("foo", "").Label("bar", "").Obj(),
+				st.MakePod().Name("p-y3").Node("node-y").Label("foo", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": false,
+				"node-b": true,
+				"node-x": false,
+				"node-y": false,
+			},
+		},
+		{
+			// 1. pod doesn't match itself on "zone" constraint, so it can be put onto any zone
+			// 2. to fulfil "node" constraint, incoming pod can be placed on node-a or node-b
+			// intersection of (1) and (2) returns node-a and node-b
+			name: "constraints hold different labelSelectors but pod doesn't match itself on 'zone' constraint",
+			pod: st.MakePod().Name("p").Label("bar", "").
+				SpreadConstraint(1, "zone", hardSpread, st.MakeLabelSelector().Exists("foo").Obj()).
+				SpreadConstraint(1, "node", hardSpread, st.MakeLabelSelector().Exists("bar").Obj()).
+				Obj(),
+			nodes: []*v1.Node{
+				st.MakeNode().Name("node-a").Label("zone", "zone1").Label("node", "node-a").Obj(),
+				st.MakeNode().Name("node-b").Label("zone", "zone1").Label("node", "node-b").Obj(),
+				st.MakeNode().Name("node-x").Label("zone", "zone2").Label("node", "node-x").Obj(),
+				st.MakeNode().Name("node-y").Label("zone", "zone2").Label("node", "node-y").Obj(),
+			},
+			existingPods: []*v1.Pod{
+				st.MakePod().Name("p-a1").Node("node-a").Label("foo", "").Obj(),
+				st.MakePod().Name("p-x1").Node("node-x").Label("bar", "").Obj(),
+				st.MakePod().Name("p-y1").Node("node-y").Label("bar", "").Obj(),
+			},
+			fits: map[string]bool{
+				"node-a": true,
+				"node-b": true,
+				"node-x": false,
+				"node-y": false,
+			},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			nodeInfoMap := schedulernodeinfo.CreateNodeNameToInfoMap(tt.existingPods, tt.nodes)
+			meta := GetPredicateMetadata(tt.pod, nodeInfoMap)
+			for _, node := range tt.nodes {
+				fits, _, _ := EvenPodsSpreadPredicate(tt.pod, meta, nodeInfoMap[node.Name])
+				if fits != tt.fits[node.Name] {
+					t.Errorf("[%s]: expected %v got %v", node.Name, tt.fits[node.Name], fits)
+				}
+			}
+		})
+	}
+}

pkg/scheduler/algorithmprovider/defaults/defaults.go

@@ -87,6 +87,12 @@ func ApplyFeatureGates() {
 		klog.Infof("TaintNodesByCondition is enabled, PodToleratesNodeTaints predicate is mandatory")
 	}
 
+	// Only register EvenPodsSpreadPredicate if the feature is enabled
+	if utilfeature.DefaultFeatureGate.Enabled(features.EvenPodsSpread) {
+		factory.InsertPredicateKeyToAlgorithmProviderMap(predicates.EvenPodsSpreadPred)
+		factory.RegisterFitPredicate(predicates.EvenPodsSpreadPred, predicates.EvenPodsSpreadPredicate)
+	}
+
 	// Prioritizes nodes that satisfy pod's resource limits
 	if utilfeature.DefaultFeatureGate.Enabled(features.ResourceLimitsPriorityFunction) {
 		klog.Infof("Registering resourcelimits priority function")

pkg/scheduler/core/generic_scheduler_test.go

@@ -228,6 +228,7 @@ func TestGenericScheduler(t *testing.T) {
 		pvcs                     []*v1.PersistentVolumeClaim
 		pod                      *v1.Pod
 		pods                     []*v1.Pod
+		buildPredMeta            bool // build predicates metadata or not
 		expectedHosts            sets.String
 		expectsErr               bool
 		wErr                     error
@@ -435,6 +436,108 @@ func TestGenericScheduler(t *testing.T) {
 			name:         "test error with priority map",
 			wErr:         errors.NewAggregate([]error{errPrioritize, errPrioritize}),
 		},
+		{
+			name: "test even pods spread predicate - 2 nodes with maxskew=1",
+			predicates: map[string]algorithmpredicates.FitPredicate{
+				"matches": algorithmpredicates.EvenPodsSpreadPredicate,
+			},
+			// prioritizers:  []priorities.PriorityConfig{{Map: EqualPriorityMap, Weight: 1}},
+			nodes: []string{"machine1", "machine2"},
+			pod: &v1.Pod{
+				ObjectMeta: metav1.ObjectMeta{Name: "p", UID: types.UID("p"), Labels: map[string]string{"foo": ""}},
+				Spec: v1.PodSpec{
+					TopologySpreadConstraints: []v1.TopologySpreadConstraint{
+						{
+							MaxSkew:           1,
+							TopologyKey:       "hostname",
+							WhenUnsatisfiable: v1.DoNotSchedule,
+							LabelSelector: &metav1.LabelSelector{
+								MatchExpressions: []metav1.LabelSelectorRequirement{
+									{
+										Key:      "foo",
+										Operator: metav1.LabelSelectorOpExists,
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			pods: []*v1.Pod{
+				{
+					ObjectMeta: metav1.ObjectMeta{Name: "pod1", UID: types.UID("pod1"), Labels: map[string]string{"foo": ""}},
+					Spec: v1.PodSpec{
+						NodeName: "machine1",
+					},
+					Status: v1.PodStatus{
+						Phase: v1.PodRunning,
+					},
+				},
+			},
+			buildPredMeta: true,
+			expectedHosts: sets.NewString("machine2"),
+			wErr:          nil,
+		},
+		{
+			name: "test even pods spread predicate - 3 nodes with maxskew=2",
+			predicates: map[string]algorithmpredicates.FitPredicate{
+				"matches": algorithmpredicates.EvenPodsSpreadPredicate,
+			},
+			// prioritizers:  []priorities.PriorityConfig{{Map: EqualPriorityMap, Weight: 1}},
+			nodes: []string{"machine1", "machine2", "machine3"},
+			pod: &v1.Pod{
+				ObjectMeta: metav1.ObjectMeta{Name: "p", UID: types.UID("p"), Labels: map[string]string{"foo": ""}},
+				Spec: v1.PodSpec{
+					TopologySpreadConstraints: []v1.TopologySpreadConstraint{
+						{
+							MaxSkew:           2,
+							TopologyKey:       "hostname",
+							WhenUnsatisfiable: v1.DoNotSchedule,
+							LabelSelector: &metav1.LabelSelector{
+								MatchExpressions: []metav1.LabelSelectorRequirement{
+									{
+										Key:      "foo",
+										Operator: metav1.LabelSelectorOpExists,
+									},
+								},
+							},
+						},
+					},
+				},
+			},
+			pods: []*v1.Pod{
+				{
+					ObjectMeta: metav1.ObjectMeta{Name: "pod1a", UID: types.UID("pod1a"), Labels: map[string]string{"foo": ""}},
+					Spec: v1.PodSpec{
+						NodeName: "machine1",
+					},
+					Status: v1.PodStatus{
+						Phase: v1.PodRunning,
+					},
+				},
+				{
+					ObjectMeta: metav1.ObjectMeta{Name: "pod1b", UID: types.UID("pod1b"), Labels: map[string]string{"foo": ""}},
+					Spec: v1.PodSpec{
+						NodeName: "machine1",
+					},
+					Status: v1.PodStatus{
+						Phase: v1.PodRunning,
+					},
+				},
+				{
+					ObjectMeta: metav1.ObjectMeta{Name: "pod2", UID: types.UID("pod2"), Labels: map[string]string{"foo": ""}},
+					Spec: v1.PodSpec{
+						NodeName: "machine2",
+					},
+					Status: v1.PodStatus{
+						Phase: v1.PodRunning,
+					},
+				},
+			},
+			buildPredMeta: true,
+			expectedHosts: sets.NewString("machine2", "machine3"),
+			wErr:          nil,
+		},
 	}
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
@@ -443,18 +546,24 @@ func TestGenericScheduler(t *testing.T) {
 				cache.AddPod(pod)
 			}
 			for _, name := range test.nodes {
-				cache.AddNode(&v1.Node{ObjectMeta: metav1.ObjectMeta{Name: name}})
+				cache.AddNode(&v1.Node{ObjectMeta: metav1.ObjectMeta{Name: name, Labels: map[string]string{"hostname": name}}})
 			}
 			pvcs := []*v1.PersistentVolumeClaim{}
 			pvcs = append(pvcs, test.pvcs...)
 
 			pvcLister := schedulertesting.FakePersistentVolumeClaimLister(pvcs)
 
+			var predMetaProducer algorithmpredicates.PredicateMetadataProducer
+			if test.buildPredMeta {
+				predMetaProducer = algorithmpredicates.NewPredicateMetadataFactory(schedulertesting.FakePodLister(test.pods))
+			} else {
+				predMetaProducer = algorithmpredicates.EmptyPredicateMetadataProducer
+			}
 			scheduler := NewGenericScheduler(
 				cache,
 				internalqueue.NewSchedulingQueue(nil, nil),
 				test.predicates,
-				algorithmpredicates.EmptyPredicateMetadataProducer,
+				predMetaProducer,
 				test.prioritizers,
 				priorities.EmptyPriorityMetadataProducer,
 				emptyFramework,