Merge pull request kubernetes-sigs#553 from hasbro17/add-generation-predicate

✨ Add predicate for Generation change on update event

Author: k8s-ci-robot

pkg/predicate/predicate.go

@@ -40,6 +40,7 @@ type Predicate interface {
 
 var _ Predicate = Funcs{}
 var _ Predicate = ResourceVersionChangedPredicate{}
+var _ Predicate = GenerationChangedPredicate{}
 
 // Funcs is a function that implements Predicate.
 type Funcs struct {
@@ -116,3 +117,47 @@ func (ResourceVersionChangedPredicate) Update(e event.UpdateEvent) bool {
 	}
 	return true
 }
+
+// GenerationChangedPredicate implements a default update predicate function on Generation change.
+//
+// This predicate will skip update events that have no change in the object's metadata.generation field.
+// The metadata.generation field of an object is incremented by the API server when writes are made to the spec field of an object.
+// This allows a controller to ignore update events where the spec is unchanged, and only the metadata and/or status fields are changed.
+//
+// For CustomResource objects the Generation is only incremented when the status subresource is enabled.
+//
+// Caveats:
+//
+// * The assumption that the Generation is incremented only on writing to the spec does not hold for all APIs.
+// E.g For Deployment objects the Generation is also incremented on writes to the metadata.annotations field.
+// For object types other than CustomResources be sure to verify which fields will trigger a Generation increment when they are written to.
+//
+// * With this predicate, any update events with writes only to the status field will not be reconciled.
+// So in the event that the status block is overwritten or wiped by someone else the controller will not self-correct to restore the correct status.
+type GenerationChangedPredicate struct {
+	Funcs
+}
+
+// Update implements default UpdateEvent filter for validating generation change
+func (GenerationChangedPredicate) Update(e event.UpdateEvent) bool {
+	if e.MetaOld == nil {
+		log.Error(nil, "Update event has no old metadata", "event", e)
+		return false
+	}
+	if e.ObjectOld == nil {
+		log.Error(nil, "Update event has no old runtime object to update", "event", e)
+		return false
+	}
+	if e.ObjectNew == nil {
+		log.Error(nil, "Update event has no new runtime object for update", "event", e)
+		return false
+	}
+	if e.MetaNew == nil {
+		log.Error(nil, "Update event has no new metadata", "event", e)
+		return false
+	}
+	if e.MetaNew.GetGeneration() == e.MetaOld.GetGeneration() {
+		return false
+	}
+	return true
+}

pkg/predicate/predicate_test.go

@@ -308,4 +308,134 @@ var _ = Describe("Predicate", func() {
 		})
 
 	})
+
+	Describe("When checking a GenerationChangedPredicate", func() {
+		instance := predicate.GenerationChangedPredicate{}
+		Context("Where the old object doesn't have a Generation or metadata", func() {
+			It("should return false", func() {
+				new := &corev1.Pod{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:       "baz",
+						Namespace:  "biz",
+						Generation: 1,
+					}}
+
+				failEvnt := event.UpdateEvent{
+					MetaNew:   new.GetObjectMeta(),
+					ObjectNew: new,
+				}
+				Expect(instance.Create(event.CreateEvent{})).To(BeTrue())
+				Expect(instance.Delete(event.DeleteEvent{})).To(BeTrue())
+				Expect(instance.Generic(event.GenericEvent{})).To(BeTrue())
+				Expect(instance.Update(failEvnt)).To(BeFalse())
+			})
+		})
+
+		Context("Where the new object doesn't have a Generation or metadata", func() {
+			It("should return false", func() {
+				old := &corev1.Pod{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:       "baz",
+						Namespace:  "biz",
+						Generation: 1,
+					}}
+
+				failEvnt := event.UpdateEvent{
+					MetaOld:   old.GetObjectMeta(),
+					ObjectOld: old,
+				}
+				Expect(instance.Create(event.CreateEvent{})).To(BeTrue())
+				Expect(instance.Delete(event.DeleteEvent{})).To(BeTrue())
+				Expect(instance.Generic(event.GenericEvent{})).To(BeTrue())
+				Expect(instance.Update(failEvnt)).To(BeFalse())
+			})
+		})
+
+		Context("Where the Generation hasn't changed", func() {
+			It("should return false", func() {
+				new := &corev1.Pod{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:       "baz",
+						Namespace:  "biz",
+						Generation: 1,
+					}}
+
+				old := &corev1.Pod{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:       "baz",
+						Namespace:  "biz",
+						Generation: 1,
+					}}
+
+				failEvnt := event.UpdateEvent{
+					MetaOld:   old.GetObjectMeta(),
+					ObjectOld: old,
+					MetaNew:   new.GetObjectMeta(),
+					ObjectNew: new,
+				}
+				Expect(instance.Create(event.CreateEvent{})).To(BeTrue())
+				Expect(instance.Delete(event.DeleteEvent{})).To(BeTrue())
+				Expect(instance.Generic(event.GenericEvent{})).To(BeTrue())
+				Expect(instance.Update(failEvnt)).To(BeFalse())
+			})
+		})
+
+		Context("Where the Generation has changed", func() {
+			It("should return true", func() {
+				new := &corev1.Pod{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:       "baz",
+						Namespace:  "biz",
+						Generation: 1,
+					}}
+
+				old := &corev1.Pod{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:       "baz",
+						Namespace:  "biz",
+						Generation: 2,
+					}}
+				passEvt := event.UpdateEvent{
+					MetaOld:   old.GetObjectMeta(),
+					ObjectOld: old,
+					MetaNew:   new.GetObjectMeta(),
+					ObjectNew: new,
+				}
+				Expect(instance.Create(event.CreateEvent{})).To(BeTrue())
+				Expect(instance.Delete(event.DeleteEvent{})).To(BeTrue())
+				Expect(instance.Generic(event.GenericEvent{})).To(BeTrue())
+				Expect(instance.Update(passEvt)).To(BeTrue())
+			})
+		})
+
+		Context("Where the objects or metadata are missing", func() {
+
+			It("should return false", func() {
+				new := &corev1.Pod{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:       "baz",
+						Namespace:  "biz",
+						Generation: 1,
+					}}
+
+				old := &corev1.Pod{
+					ObjectMeta: metav1.ObjectMeta{
+						Name:       "baz",
+						Namespace:  "biz",
+						Generation: 1,
+					}}
+
+				failEvt1 := event.UpdateEvent{MetaOld: old.GetObjectMeta(), ObjectOld: old, MetaNew: new.GetObjectMeta()}
+				failEvt2 := event.UpdateEvent{MetaOld: old.GetObjectMeta(), MetaNew: new.GetObjectMeta(), ObjectNew: new}
+				failEvt3 := event.UpdateEvent{MetaOld: old.GetObjectMeta(), ObjectOld: old, ObjectNew: new}
+				Expect(instance.Create(event.CreateEvent{})).To(BeTrue())
+				Expect(instance.Delete(event.DeleteEvent{})).To(BeTrue())
+				Expect(instance.Generic(event.GenericEvent{})).To(BeTrue())
+				Expect(instance.Update(failEvt1)).To(BeFalse())
+				Expect(instance.Update(failEvt2)).To(BeFalse())
+				Expect(instance.Update(failEvt3)).To(BeFalse())
+			})
+		})
+
+	})
 })