✨ enable conversion webhook by default

examples/conversion/pkg/apis/jobs/v1/register.go

@@ -25,15 +25,15 @@ package v1
 
 import (
 	"k8s.io/apimachinery/pkg/runtime/schema"
-	controllers "sigs.k8s.io/controller-runtime"
+	"sigs.k8s.io/controller-runtime/pkg/scheme"
 )
 
 var (
 	// SchemeGroupVersion is group version used to register these objects
 	SchemeGroupVersion = schema.GroupVersion{Group: "jobs.example.org", Version: "v1"}
 
 	// SchemeBuilder is used to add go types to the GroupVersionKind scheme
-	SchemeBuilder = &controllers.SchemeBuilder{GroupVersion: SchemeGroupVersion}
+	SchemeBuilder = &scheme.Builder{GroupVersion: SchemeGroupVersion}
 
 	// AddToScheme is required by pkg/client/...
 	AddToScheme = SchemeBuilder.AddToScheme

examples/conversion/pkg/apis/jobs/v2/register.go

@@ -25,15 +25,15 @@ package v2
 
 import (
 	"k8s.io/apimachinery/pkg/runtime/schema"
-	controllers "sigs.k8s.io/controller-runtime"
+	"sigs.k8s.io/controller-runtime/pkg/scheme"
 )
 
 var (
 	// SchemeGroupVersion is group version used to register these objects
 	SchemeGroupVersion = schema.GroupVersion{Group: "jobs.example.org", Version: "v2"}
 
 	// SchemeBuilder is used to add go types to the GroupVersionKind scheme
-	SchemeBuilder = &controllers.SchemeBuilder{GroupVersion: SchemeGroupVersion}
+	SchemeBuilder = &scheme.Builder{GroupVersion: SchemeGroupVersion}
 
 	// AddToScheme is required by pkg/client/...
 	AddToScheme = SchemeBuilder.AddToScheme

pkg/builder/build.go

@@ -32,6 +32,7 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/reconcile"
 	"sigs.k8s.io/controller-runtime/pkg/source"
 	"sigs.k8s.io/controller-runtime/pkg/webhook/admission"
+	"sigs.k8s.io/controller-runtime/pkg/webhook/conversion"
 )
 
 // Supporting mocking out functions for testing
@@ -285,7 +286,11 @@ func (blder *Builder) doWebhook() error {
 		}
 	}
 
-	return err
+	err = conversion.CheckConvertibility(blder.mgr.GetScheme(), blder.apiType)
+	if err != nil {
+		log.Error(err, "conversion check failed", "GVK", gvk)
+	}
+	return nil
 }
 
 func generateMutatePath(gvk schema.GroupVersionKind) string {

pkg/manager/internal.go

@@ -38,6 +38,7 @@ import (
 	"sigs.k8s.io/controller-runtime/pkg/recorder"
 	"sigs.k8s.io/controller-runtime/pkg/runtime/inject"
 	"sigs.k8s.io/controller-runtime/pkg/webhook"
+	"sigs.k8s.io/controller-runtime/pkg/webhook/conversion"
 )
 
 var log = logf.RuntimeLog.WithName("manager")
@@ -191,6 +192,7 @@ func (cm *controllerManager) GetWebhookServer() *webhook.Server {
 			Port: cm.port,
 			Host: cm.host,
 		}
+		cm.webhookServer.Register("/convert", &conversion.Webhook{})
 		if err := cm.Add(cm.webhookServer); err != nil {
 			panic("unable to add webhookServer to the controller manager")
 		}

pkg/webhook/conversion/conversion.go

@@ -212,6 +212,87 @@ func (wh *Webhook) allocateDstObject(apiVersion, kind string) (runtime.Object, e
 	return obj, nil
 }
 
+// CheckConvertibility determines if given type is convertible or not. For a type
+// to be convertible, the group-kind needs to have a Hub type defined and all
+// non-hub types must be able to convert to/from Hub.
+func CheckConvertibility(scheme *runtime.Scheme, obj runtime.Object) error {
+	var hubs, spokes, nonSpokes []runtime.Object
+
+	gvks, _, err := scheme.ObjectKinds(obj)
+	if err != nil {
+		return fmt.Errorf("error retriving object kinds for given object : %v", err)
+	}
+
+	for _, gvk := range gvks {
+		instance, err := scheme.New(gvk)
+		if err != nil {
+			return fmt.Errorf("failed to allocate an instance for gvk %v %v", gvk, err)
+		}
+
+		if isHub(instance) {
+			hubs = append(hubs, instance)
+			continue
+		}
+
+		if !isConvertible(instance) {
+			nonSpokes = append(nonSpokes, instance)
+			continue
+		}
+
+		spokes = append(spokes, instance)
+	}
+
+	if len(gvks) == 1 {
+		return nil // single version
+	}
+
+	if len(hubs) == 0 && len(spokes) == 0 {
+		// multiple version detected with no conversion implementation. This is
+		// true for multi-version built-in types.
+		return nil
+	}
+
+	if len(hubs) == 1 && len(nonSpokes) == 0 { // convertible
+		spokeVersions := []string{}
+		for _, sp := range spokes {
+			spokeVersions = append(spokeVersions, sp.GetObjectKind().GroupVersionKind().String())
+		}
+		log.V(1).Info("conversion enabled for kind", "kind",
+			gvks[0].GroupKind(), "hub", hubs[0], "spokes", spokeVersions)
+		return nil
+	}
+
+	return PartialImplementationError{
+		hubs:      hubs,
+		nonSpokes: nonSpokes,
+		spokes:    spokes,
+	}
+}
+
+// PartialImplementationError represents an error due to partial conversion
+// implementation such as hub without spokes, multiple hubs or spokes without hub.
+type PartialImplementationError struct {
+	gvk       schema.GroupVersionKind
+	hubs      []runtime.Object
+	nonSpokes []runtime.Object
+	spokes    []runtime.Object
+}
+
+func (e PartialImplementationError) Error() string {
+	if len(e.hubs) == 0 {
+		return fmt.Sprintf("no hub defined for gvk %s", e.gvk)
+	}
+	if len(e.hubs) > 1 {
+		return fmt.Sprintf("multiple(%d) hubs defined for group-kind '%s' ",
+			len(e.hubs), e.gvk.GroupKind())
+	}
+	if len(e.nonSpokes) > 0 {
+		return fmt.Sprintf("%d inconvertible types detected for group-kind '%s'",
+			len(e.nonSpokes), e.gvk.GroupKind())
+	}
+	return ""
+}
+
 // isHub determines if passed-in object is a Hub or not.
 func isHub(obj runtime.Object) bool {
 	_, yes := obj.(conversion.Hub)

pkg/webhook/conversion/conversion_test.go

@@ -200,3 +200,39 @@ var _ = Describe("Conversion Webhook", func() {
 	})
 
 })
+
+var _ = Describe("Convertibility Check", func() {
+
+	var scheme *runtime.Scheme
+
+	BeforeEach(func() {
+
+		scheme = kscheme.Scheme
+		Expect(jobsapis.AddToScheme(scheme)).To(Succeed())
+
+	})
+
+	It("should not return error for convertible types", func() {
+		obj := &jobsv2.ExternalJob{
+			TypeMeta: metav1.TypeMeta{
+				Kind:       "ExternalJob",
+				APIVersion: "jobs.example.org/v2",
+			},
+		}
+
+		err := CheckConvertibility(scheme, obj)
+		Expect(err).NotTo(HaveOccurred())
+	})
+
+	It("should not return error for a built-in multi-version type", func() {
+		obj := &appsv1beta1.Deployment{
+			TypeMeta: metav1.TypeMeta{
+				Kind:       "Deployment",
+				APIVersion: "apps/v1beta1",
+			},
+		}
+
+		err := CheckConvertibility(scheme, obj)
+		Expect(err).NotTo(HaveOccurred())
+	})
+})