Let GC print specific message for RESTMapping failure

pkg/controller/garbagecollector/garbagecollector.go

@@ -143,6 +143,12 @@ func (gc *GarbageCollector) attemptToDeleteWorker() bool {
 	}
 	err := gc.attemptToDeleteItem(n)
 	if err != nil {
+		// TODO: remove this block when gc starts using dynamic RESTMapper.
+		if restMappingError, ok := err.(*restMappingError); ok {
+			utilruntime.HandleError(fmt.Errorf("Ignore syncing item %#v: %s", n, restMappingError.Message()))
+			// The RESTMapper is static, so no need to retry, otherwise we'll get the same error.
+			return true
+		}
 		utilruntime.HandleError(fmt.Errorf("Error syncing item %#v: %v", n, err))
 		// retry if garbage collection of an object failed.
 		gc.attemptToDelete.AddRateLimited(item)

pkg/controller/garbagecollector/operations.go

@@ -30,13 +30,36 @@ import (
 	"k8s.io/kubernetes/pkg/client/retry"
 )
 
+type restMappingError struct {
+	kind    string
+	version string
+}
+
+func (r *restMappingError) Error() string {
+	versionKind := fmt.Sprintf("%s/%s", r.version, r.kind)
+	return fmt.Sprintf("unable to get REST mapping for %s.", versionKind)
+}
+
+// Message prints more details
+func (r *restMappingError) Message() string {
+	versionKind := fmt.Sprintf("%s/%s", r.version, r.kind)
+	errMsg := fmt.Sprintf("unable to get REST mapping for %s.", versionKind)
+	errMsg += fmt.Sprintf(" If %s is a thirdparty resource (tpr), please note that the garbage collector doesn't support tpr yet. Once tpr is supported, object with ownerReferences referring non-existing tpr objects will be deleted by the garbage collector.", versionKind)
+	errMsg += fmt.Sprintf(" If %s is not a tpr, then you should remove ownerReferences that refer %s objects manually.", versionKind, versionKind)
+	return errMsg
+}
+
+func newRESTMappingError(kind, version string) *restMappingError {
+	return &restMappingError{kind: kind, version: version}
+}
+
 // apiResource consults the REST mapper to translate an <apiVersion, kind,
 // namespace> tuple to a unversioned.APIResource struct.
 func (gc *GarbageCollector) apiResource(apiVersion, kind string, namespaced bool) (*metav1.APIResource, error) {
 	fqKind := schema.FromAPIVersionAndKind(apiVersion, kind)
 	mapping, err := gc.restMapper.RESTMapping(fqKind.GroupKind(), apiVersion)
 	if err != nil {
-		return nil, fmt.Errorf("unable to get REST mapping for kind: %s, version: %s", kind, apiVersion)
+		return nil, newRESTMappingError(kind, apiVersion)
 	}
 	glog.V(5).Infof("map kind %s, version %s to resource %s", kind, apiVersion, mapping.Resource)
 	resource := metav1.APIResource{