EvenPodsSpread: Define a new Predicate

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")
+	// ErrSpreadConstraintsNotMatch is used for EvenPodsSpread predicate error.
+	ErrSpreadConstraintsNotMatch = newPredicateFailureError("EvenPodsSpread", "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 +1714,17 @@ 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
+	}
+	return true, nil, nil
+}

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")