fix: Exclude duplicated resource types

When resource types migrate to a new API group, its old version will
still be accessible for the next few versions of Kubernetes
(eg. "events.v1" -> "events.v1.events.k8s.io") so we filter them out to
avoid wasting effort on processing the same set of objects received
from the resource's old & new API twice.

Signed-off-by: Justin Toh <tohjustin@hotmail.com>

pkg/cmd/lineage/lineage.go

@@ -234,10 +234,19 @@ func (o *CmdOptions) getAPIResources() ([]Resource, error) {
 			continue
 		}
 		for _, resource := range list.APIResources {
-			// filter resources that can be watched, listed & get
+			// Filter resources that can be watched, listed & get
 			if len(resource.Verbs) == 0 || !sets.NewString(resource.Verbs...).HasAll("watch", "list", "get") {
 				continue
 			}
+			// Exclude duplicated resources (for Kubernetes v1.18 & above)
+			switch {
+			// migrated to "events.v1.events.k8s.io"
+			case gv.Group == "" && resource.Name == "events":
+				continue
+			// migrated to "ingresses.v1.networking.k8s.io"
+			case gv.Group == "extensions" && resource.Name == "ingresses":
+				continue
+			}
 			resources = append(resources, Resource{
 				APIGroupVersionResource: schema.GroupVersionResource{
 					Group:    gv.Group,