add option to orphan objects on deletion

an annotation <operator.name>/delete-policy: ""|default|oprhan can now be set on objects;
if the value is empty or 'default', then the normal behavior applies; in case it is 'orphan',
the object will just stay instead of being deleted (and it will be no longer tracked or
considered as dependent of the component)

Author: cbarbian-sap

pkg/component/reconcile.go

@@ -475,6 +475,7 @@ type reconcileTarget[T Component] struct {
 	annotationKeyDigest          string
 	annotationKeyReconcilePolicy string
 	annotationKeyUpdatePolicy    string
+	annotationKeyDeletePolicy    string
 	annotationKeyOrder           string
 	annotationKeyPurgeOrder      string
 	annotationKeyOwnerId         string
@@ -490,6 +491,7 @@ func newReconcileTarget[T Component](reconcilerName string, reconcilerId string,
 		annotationKeyDigest:          reconcilerName + "/" + types.AnnotationKeySuffixDigest,
 		annotationKeyReconcilePolicy: reconcilerName + "/" + types.AnnotationKeySuffixReconcilePolicy,
 		annotationKeyUpdatePolicy:    reconcilerName + "/" + types.AnnotationKeySuffixUpdatePolicy,
+		annotationKeyDeletePolicy:    reconcilerName + "/" + types.AnnotationKeySuffixDeletePolicy,
 		annotationKeyOrder:           reconcilerName + "/" + types.AnnotationKeySuffixOrder,
 		annotationKeyPurgeOrder:      reconcilerName + "/" + types.AnnotationKeySuffixPurgeOrder,
 		annotationKeyOwnerId:         reconcilerName + "/" + types.AnnotationKeySuffixOwnerId,
@@ -781,9 +783,17 @@ func (t *reconcileTarget[T]) Reconcile(ctx context.Context, component T) (bool,
 				return false, errors.Wrapf(err, "error reading object %s", item)
 			}
 
+			orphan := false
+			if existingObject != nil {
+				orphan = existingObject.GetAnnotations()[t.annotationKeyDeletePolicy] == types.DeletePolicyOrphan
+			}
+
 			switch item.Phase {
 			case PhaseScheduledForDeletion:
 				if numManagedToBeDeleted == 0 || t.isManaged(item, component) {
+					if orphan {
+						continue
+					}
 					// note: here is a theoretical risk that we delete an existing foreign object, because informers are not yet synced
 					// however not sending the delete request is also not an option, because this might lead to orphaned own dependents
 					if err := t.deleteObject(ctx, item, existingObject); err != nil {
@@ -795,6 +805,9 @@ func (t *reconcileTarget[T]) Reconcile(ctx context.Context, component T) (bool,
 				numToBeDeleted++
 			case PhaseScheduledForCompletion:
 				if numManagedToBeDeleted == 0 || t.isManaged(item, component) {
+					if orphan {
+						return false, fmt.Errorf("invalid usage of deletion policy: object %s is scheduled for completion (due to purge order) and therefore cannot be orphaned", item)
+					}
 					// note: here is a theoretical risk that we delete an existing foreign object, because informers are not yet synced
 					// however not sending the delete request is also not an option, because this might lead to orphaned own dependents
 					if err := t.deleteObject(ctx, item, existingObject); err != nil {
@@ -994,6 +1007,10 @@ func (t *reconcileTarget[T]) Delete(ctx context.Context, component T) (bool, err
 		}
 
 		if numManaged == 0 || t.isManaged(item, component) {
+			// orphan the object, if according deletion policy is set
+			if existingObject != nil && existingObject.GetAnnotations()[t.annotationKeyDeletePolicy] == types.DeletePolicyOrphan {
+				continue
+			}
 			// delete the object
 			// note: here is a theoretical risk that we delete an existing (foreign) object, because informers are not yet synced
 			// however not sending the delete request is also not an option, because this might lead to orphaned own dependents

pkg/types/constants.go

@@ -10,6 +10,7 @@ const (
 	AnnotationKeySuffixDigest          = "digest"
 	AnnotationKeySuffixReconcilePolicy = "reconcile-policy"
 	AnnotationKeySuffixUpdatePolicy    = "update-policy"
+	AnnotationKeySuffixDeletePolicy    = "delete-policy"
 	AnnotationKeySuffixOrder           = "order"
 	AnnotationKeySuffixPurgeOrder      = "purge-order"
 	AnnotationKeySuffixOwnerId         = "owner-id"
@@ -25,3 +26,8 @@ const (
 	UpdatePolicyDefault  = "default"
 	UpdatePolicyRecreate = "recreate"
 )
+
+const (
+	DeletePolicyDefault = "default"
+	DeletePolicyOrphan  = "orphan"
+)

website/content/en/docs/concepts/dependents.md

@@ -26,6 +26,9 @@ To support such cases, the `Generator` implementation can set the following anno
 - `mycomponent-operator.mydomain.io/update-policy`: defines how the object (if existing) is updated; can be one of:
   - `default` (which is the default): a regular update (i.e. PUT) call will be made to the Kubernetes API server
   - `recreate`: if the object would be updated, it will be deleted and recreated instead
+- `mycomponent-operator.mydomain.io/delete-policy`: defines what happens if the object is deleted; can be one of:
+  - `default` (which is the default): a delete call will be sent to the Kubernetes API server
+  - `orphan`: the object will not be deleted, and it will be no longer tracked
 - `mycomponent-operator.mydomain.io/order`: the order at which this object will be reconciled; dependents will be reconciled order by order; that is, objects of the same order will be deployed in the canonical order, and the controller will only proceed to the next order if all objects of previous orders are ready; specified orders can be negative or positive numbers between -32768 and 32767, objects with no explicit order set are treated as if they would specify order 0.
 - `mycomponent-operator.mydomain.io/purge-order`: (optional) the order by which this object will be purged