Introduce a mechanism to scheduler to actively trigger rescheduling

api/openapi-spec/swagger.json

@@ -19151,6 +19151,10 @@
             "$ref": "#/definitions/com.github.karmada-io.karmada.pkg.apis.work.v1alpha2.BindingSnapshot"
           }
         },
+        "rescheduleTriggeredAt": {
+          "description": "RescheduleTriggeredAt is a timestamp representing when the referenced resource is triggered rescheduling. When this field is updated, it means a rescheduling is manually triggered by user, and the expected behavior of this action is to do a complete recalculation without referring to last scheduling results. It works with the status.lastScheduledTime field, and only when this timestamp is later than timestamp in status.lastScheduledTime will the rescheduling actually execute, otherwise, ignored.\n\nIt is represented in RFC3339 form (like '2006-01-02T15:04:05Z') and is in UTC.",
+          "$ref": "#/definitions/io.k8s.apimachinery.pkg.apis.meta.v1.Time"
+        },
         "resource": {
           "description": "Resource represents the Kubernetes resource to be propagated.",
           "default": {},
@@ -19182,6 +19186,10 @@
             "$ref": "#/definitions/io.k8s.apimachinery.pkg.apis.meta.v1.Condition"
           }
         },
+        "lastScheduledTime": {
+          "description": "LastScheduledTime representing the latest timestamp when scheduler successfully finished a scheduling. It is represented in RFC3339 form (like '2006-01-02T15:04:05Z') and is in UTC.",
+          "$ref": "#/definitions/io.k8s.apimachinery.pkg.apis.meta.v1.Time"
+        },
         "schedulerObservedGeneration": {
           "description": "SchedulerObservedGeneration is the generation(.metadata.generation) observed by the scheduler. If SchedulerObservedGeneration is less than the generation in metadata means the scheduler hasn't confirmed the scheduling result or hasn't done the schedule yet.",
           "type": "integer",

charts/karmada/_crds/bases/work/work.karmada.io_clusterresourcebindings.yaml

@@ -1128,6 +1128,18 @@ spec:
                   - name
                   type: object
                 type: array
+              rescheduleTriggeredAt:
+                description: "RescheduleTriggeredAt is a timestamp representing when
+                  the referenced resource is triggered rescheduling. When this field
+                  is updated, it means a rescheduling is manually triggered by user,
+                  and the expected behavior of this action is to do a complete recalculation
+                  without referring to last scheduling results. It works with the
+                  status.lastScheduledTime field, and only when this timestamp is
+                  later than timestamp in status.lastScheduledTime will the rescheduling
+                  actually execute, otherwise, ignored. \n It is represented in RFC3339
+                  form (like '2006-01-02T15:04:05Z') and is in UTC."
+                format: date-time
+                type: string
               resource:
                 description: Resource represents the Kubernetes resource to be propagated.
                 properties:
@@ -1279,6 +1291,12 @@ spec:
                   - type
                   type: object
                 type: array
+              lastScheduledTime:
+                description: LastScheduledTime representing the latest timestamp when
+                  scheduler successfully finished a scheduling. It is represented
+                  in RFC3339 form (like '2006-01-02T15:04:05Z') and is in UTC.
+                format: date-time
+                type: string
               schedulerObservedGeneration:
                 description: SchedulerObservedGeneration is the generation(.metadata.generation)
                   observed by the scheduler. If SchedulerObservedGeneration is less

charts/karmada/_crds/bases/work/work.karmada.io_resourcebindings.yaml

@@ -1128,6 +1128,18 @@ spec:
                   - name
                   type: object
                 type: array
+              rescheduleTriggeredAt:
+                description: "RescheduleTriggeredAt is a timestamp representing when
+                  the referenced resource is triggered rescheduling. When this field
+                  is updated, it means a rescheduling is manually triggered by user,
+                  and the expected behavior of this action is to do a complete recalculation
+                  without referring to last scheduling results. It works with the
+                  status.lastScheduledTime field, and only when this timestamp is
+                  later than timestamp in status.lastScheduledTime will the rescheduling
+                  actually execute, otherwise, ignored. \n It is represented in RFC3339
+                  form (like '2006-01-02T15:04:05Z') and is in UTC."
+                format: date-time
+                type: string
               resource:
                 description: Resource represents the Kubernetes resource to be propagated.
                 properties:
@@ -1279,6 +1291,12 @@ spec:
                   - type
                   type: object
                 type: array
+              lastScheduledTime:
+                description: LastScheduledTime representing the latest timestamp when
+                  scheduler successfully finished a scheduling. It is represented
+                  in RFC3339 form (like '2006-01-02T15:04:05Z') and is in UTC.
+                format: date-time
+                type: string
               schedulerObservedGeneration:
                 description: SchedulerObservedGeneration is the generation(.metadata.generation)
                   observed by the scheduler. If SchedulerObservedGeneration is less

pkg/apis/work/v1alpha2/binding_types.go

@@ -136,6 +136,16 @@ type ResourceBindingSpec struct {
 	// +kubebuilder:validation:Enum=Abort;Overwrite
 	// +optional
 	ConflictResolution policyv1alpha1.ConflictResolution `json:"conflictResolution,omitempty"`
+
+	// RescheduleTriggeredAt is a timestamp representing when the referenced resource is triggered rescheduling.
+	// When this field is updated, it means a rescheduling is manually triggered by user, and the expected behavior
+	// of this action is to do a complete recalculation without referring to last scheduling results.
+	// It works with the status.lastScheduledTime field, and only when this timestamp is later than timestamp in
+	// status.lastScheduledTime will the rescheduling actually execute, otherwise, ignored.
+	//
+	// It is represented in RFC3339 form (like '2006-01-02T15:04:05Z') and is in UTC.
+	// +optional
+	RescheduleTriggeredAt *metav1.Time `json:"rescheduleTriggeredAt,omitempty"`
 }
 
 // ObjectReference contains enough information to locate the referenced object inside current cluster.
@@ -297,6 +307,11 @@ type ResourceBindingStatus struct {
 	// +optional
 	SchedulerObservedAffinityName string `json:"schedulerObservingAffinityName,omitempty"`
 
+	// LastScheduledTime representing the latest timestamp when scheduler successfully finished a scheduling.
+	// It is represented in RFC3339 form (like '2006-01-02T15:04:05Z') and is in UTC.
+	// +optional
+	LastScheduledTime *metav1.Time `json:"lastScheduledTime,omitempty"`
+
 	// Conditions contain the different condition statuses.
 	// +optional
 	Conditions []metav1.Condition `json:"conditions,omitempty"`

pkg/scheduler/core/assignment.go

@@ -49,6 +49,22 @@ const (
 	DynamicWeightStrategy = "DynamicWeight"
 )
 
+// assignmentMode indicates how to assign replicas, especially in case of re-assignment.
+type assignmentMode string
+
+const (
+	// Steady represents a steady, incremental approach to re-assign replicas
+	// across clusters. It aims to maintain the exist replicas distribution as
+	// closely as possible, only making minimal adjustments when necessary.
+	// It minimizes disruptions and preserves the balance across clusters.
+	Steady assignmentMode = "Steady"
+
+	// Fresh means that disregards the previous assignment entirely and
+	// seeks to establish an entirely new replica distribution across clusters.
+	// It is willing to accept significant changes even if it involves disruption.
+	Fresh assignmentMode = "Fresh"
+)
+
 // assignState is a wrapper of the input for assigning function.
 type assignState struct {
 	candidates []*clusterv1alpha1.Cluster
@@ -58,6 +74,9 @@ type assignState struct {
 	// fields below are indirect results
 	strategyType string
 
+	// assignmentMode represents the mode how to assign replicas
+	assignmentMode assignmentMode
+
 	scheduledClusters []workv1alpha2.TargetCluster
 	assignedReplicas  int32
 	availableClusters []workv1alpha2.TargetCluster
@@ -67,26 +86,35 @@ type assignState struct {
 	targetReplicas int32
 }
 
-func newAssignState(candidates []*clusterv1alpha1.Cluster, placement *policyv1alpha1.Placement, obj *workv1alpha2.ResourceBindingSpec) *assignState {
+func newAssignState(candidates []*clusterv1alpha1.Cluster, spec *workv1alpha2.ResourceBindingSpec,
+	status *workv1alpha2.ResourceBindingStatus) *assignState {
 	var strategyType string
 
-	switch placement.ReplicaSchedulingType() {
+	switch spec.Placement.ReplicaSchedulingType() {
 	case policyv1alpha1.ReplicaSchedulingTypeDuplicated:
 		strategyType = DuplicatedStrategy
 	case policyv1alpha1.ReplicaSchedulingTypeDivided:
-		switch placement.ReplicaScheduling.ReplicaDivisionPreference {
+		switch spec.Placement.ReplicaScheduling.ReplicaDivisionPreference {
 		case policyv1alpha1.ReplicaDivisionPreferenceAggregated:
 			strategyType = AggregatedStrategy
 		case policyv1alpha1.ReplicaDivisionPreferenceWeighted:
-			if placement.ReplicaScheduling.WeightPreference != nil && len(placement.ReplicaScheduling.WeightPreference.DynamicWeight) != 0 {
+			if spec.Placement.ReplicaScheduling.WeightPreference != nil && len(spec.Placement.ReplicaScheduling.WeightPreference.DynamicWeight) != 0 {
 				strategyType = DynamicWeightStrategy
 			} else {
 				strategyType = StaticWeightStrategy
 			}
 		}
 	}
 
-	return &assignState{candidates: candidates, strategy: placement.ReplicaScheduling, spec: obj, strategyType: strategyType}
+	// the assignment mode is defaults to Steady to minimizes disruptions and preserves the balance across clusters.
+	expectAssignmentMode := Steady
+	// when spec.rescheduleTriggeredAt is updated, it represents a rescheduling is manually triggered by user, and the
+	// expected behavior of this action is to do a complete recalculation without referring to last scheduling results.
+	if util.RescheduleRequired(spec.RescheduleTriggeredAt, status.LastScheduledTime) {
+		expectAssignmentMode = Fresh
+	}
+
+	return &assignState{candidates: candidates, strategy: spec.Placement.ReplicaScheduling, spec: spec, strategyType: strategyType, assignmentMode: expectAssignmentMode}
 }
 
 func (as *assignState) buildScheduledClusters() {
@@ -179,6 +207,17 @@ func assignByStaticWeightStrategy(state *assignState) ([]workv1alpha2.TargetClus
 
 func assignByDynamicStrategy(state *assignState) ([]workv1alpha2.TargetCluster, error) {
 	state.buildScheduledClusters()
+
+	// 1. when Fresh mode expected, do a complete recalculation without referring to the last scheduling results.
+	if state.assignmentMode == Fresh {
+		result, err := dynamicFreshScale(state)
+		if err != nil {
+			return nil, fmt.Errorf("failed to do fresh scale: %v", err)
+		}
+		return result, nil
+	}
+
+	// 2. when Steady mode expected, try minimizing large changes in scheduling results.
 	if state.assignedReplicas > state.spec.Replicas {
 		// We need to reduce the replicas in terms of the previous result.
 		result, err := dynamicScaleDown(state)