Detect priority change happend on PropagationPolicy

and enqueue PropagationPolicy that could repreempte.

Signed-off-by: RainbowMango <qdurenhongcai@gmail.com>

pkg/detector/detector.go

@@ -31,6 +31,7 @@ import (
 	policyv1alpha1 "github.com/karmada-io/karmada/pkg/apis/policy/v1alpha1"
 	workv1alpha2 "github.com/karmada-io/karmada/pkg/apis/work/v1alpha2"
 	"github.com/karmada-io/karmada/pkg/events"
+	"github.com/karmada-io/karmada/pkg/features"
 	"github.com/karmada-io/karmada/pkg/metrics"
 	"github.com/karmada-io/karmada/pkg/resourceinterpreter"
 	"github.com/karmada-io/karmada/pkg/sharedcli/ratelimiterflag"
@@ -783,7 +784,7 @@ func (d *ResourceDetector) OnPropagationPolicyAdd(obj interface{}) {
 }
 
 // OnPropagationPolicyUpdate handles object update event and push the object to queue.
-func (d *ResourceDetector) OnPropagationPolicyUpdate(_, newObj interface{}) {
+func (d *ResourceDetector) OnPropagationPolicyUpdate(oldObj, newObj interface{}) {
 	key, err := ClusterWideKeyFunc(newObj)
 	if err != nil {
 		return
@@ -791,6 +792,52 @@ func (d *ResourceDetector) OnPropagationPolicyUpdate(_, newObj interface{}) {
 
 	klog.V(2).Infof("Update PropagationPolicy(%s)", key)
 	d.policyReconcileWorker.Add(key)
+
+	// Temporary solution of corner case: After the priority(.spec.priority) of
+	// PropagationPolicy changed from high priority (e.g. 5) to low priority(e.g. 3),
+	// we should try to check if there is a PropagationPolicy(e.g. with priority 4)
+	// could preempt the targeted resources.
+	//
+	// Recognized limitations of the temporary solution are:
+	// - Too much logical processed in an event handler function will slow down
+	//   the overall reconcile speed.
+	// - If there is an error raised during the process, the event will be lost
+	//   and no second chance to retry.
+	//
+	// The idea of the long-term solution, perhaps PropagationPolicy could have
+	// a status, in that case we can record the observed priority(.status.observedPriority)
+	// which can be used to detect priority changes during reconcile logic.
+	if features.FeatureGate.Enabled(features.PolicyPreemption) {
+		var unstructuredOldObj *unstructured.Unstructured
+		var unstructuredNewObj *unstructured.Unstructured
+
+		unstructuredOldObj, err = helper.ToUnstructured(oldObj)
+		if err != nil {
+			klog.Errorf("Failed to transform oldObj, error: %v", err)
+			return
+		}
+		unstructuredNewObj, err = helper.ToUnstructured(newObj)
+		if err != nil {
+			klog.Errorf("Failed to transform newObj, error: %v", err)
+			return
+		}
+
+		var oldPolicy policyv1alpha1.PropagationPolicy
+		var newPolicy policyv1alpha1.PropagationPolicy
+
+		if err = helper.ConvertToTypedObject(unstructuredOldObj, &oldPolicy); err != nil {
+			klog.Errorf("Failed to convert typed PropagationPolicy(%s/%s): %v", unstructuredOldObj.GetNamespace(), unstructuredOldObj.GetName(), err)
+			return
+		}
+		if err = helper.ConvertToTypedObject(unstructuredNewObj, &newPolicy); err != nil {
+			klog.Errorf("Failed to convert typed PropagationPolicy(%s/%s): %v", newPolicy.GetNamespace(), newPolicy.GetName(), err)
+			return
+		}
+
+		if newPolicy.ExplicitPriority() < oldPolicy.ExplicitPriority() {
+			d.HandleDeprioritizedPropagationPolicy(oldPolicy, newPolicy)
+		}
+	}
 }
 
 // OnPropagationPolicyDelete handles object delete event and push the object to queue.

pkg/detector/preemption.go

@@ -4,6 +4,7 @@ import (
 	corev1 "k8s.io/api/core/v1"
 	apierrors "k8s.io/apimachinery/pkg/api/errors"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
+	"k8s.io/apimachinery/pkg/labels"
 	utilerrors "k8s.io/apimachinery/pkg/util/errors"
 	"k8s.io/klog/v2"
 
@@ -227,3 +228,46 @@ func (d *ResourceDetector) fetchResourceTemplate(rs policyv1alpha1.ResourceSelec
 	}
 	return resourceTemplate, nil
 }
+
+// HandleDeprioritizedPropagationPolicy responses to priority change of a PropagationPolicy,
+// if the change is from high priority (e.g. 5) to low priority(e.g. 3), it will
+// check if there is another PropagationPolicy could preempt the targeted resource,
+// and put the PropagationPolicy in the queue to trigger preemption.
+func (d *ResourceDetector) HandleDeprioritizedPropagationPolicy(oldPolicy policyv1alpha1.PropagationPolicy, newPolicy policyv1alpha1.PropagationPolicy) {
+	klog.Infof("PropagationPolicy(%s/%s) priority changed from %d to %d", newPolicy.GetNamespace(), newPolicy.GetName(), *oldPolicy.Spec.Priority, *newPolicy.Spec.Priority)
+	policies, err := d.propagationPolicyLister.ByNamespace(newPolicy.GetNamespace()).List(labels.Everything())
+	if err != nil {
+		klog.Errorf("Failed to list PropagationPolicy from namespace: %s, error: %v", newPolicy.GetNamespace(), err)
+		return
+	}
+
+	// TODO(@RainbowMango): Should sort the listed policies to ensure the
+	// higher priority PropagationPolicy be process first to avoid possible
+	// multiple preemption.
+
+	for i := range policies {
+		var potentialPolicy policyv1alpha1.PropagationPolicy
+		if err = helper.ConvertToTypedObject(policies[i], &potentialPolicy); err != nil {
+			klog.Errorf("Failed to convert typed PropagationPolicy: %v", err)
+			continue
+		}
+		// Re-queue the polies that enables preemption and with the priority
+		// in range (new priority, old priority).
+		// For the polices with higher priority than old priority, it can
+		// perform preempt automatically and don't need to re-queue here.
+		// For the polices with lower priority than new priority, it can't
+		// perform preempt as insufficient priority.
+		if potentialPolicy.Spec.Priority != nil &&
+			potentialPolicy.Spec.Preemption == policyv1alpha1.PreemptAlways &&
+			potentialPolicy.ExplicitPriority() > newPolicy.ExplicitPriority() &&
+			potentialPolicy.ExplicitPriority() < oldPolicy.ExplicitPriority() {
+			var potentialKey util.QueueKey
+			potentialKey, err = ClusterWideKeyFunc(&potentialPolicy)
+			if err != nil {
+				return
+			}
+			klog.Infof("Enqueuing PropagationPolicy(%s/%s) in case of PropagationPolicy(%s/%s) priority changes", potentialPolicy.GetNamespace(), potentialPolicy.GetName(), newPolicy.GetNamespace(), newPolicy.GetName())
+			d.policyReconcileWorker.Add(potentialKey)
+		}
+	}
+}