introduce resize REST object

This commit introduces a basic REST object for resize subresource and
adds it to the pod storage.

pkg/registry/core/pod/storage/storage.go

@@ -54,6 +54,7 @@ type PodStorage struct {
 	Eviction            *EvictionREST
 	Status              *StatusREST
 	EphemeralContainers *EphemeralContainersREST
+	Resize              *ResizeREST
 	Log                 *podrest.LogREST
 	Proxy               *podrest.ProxyREST
 	Exec                *podrest.ExecREST
@@ -100,6 +101,8 @@ func NewStorage(optsGetter generic.RESTOptionsGetter, k client.ConnectionInfoGet
 	statusStore.ResetFieldsStrategy = registrypod.StatusStrategy
 	ephemeralContainersStore := *store
 	ephemeralContainersStore.UpdateStrategy = registrypod.EphemeralContainersStrategy
+	resizeStore := *store
+	resizeStore.UpdateStrategy = registrypod.ResizeStrategy
 
 	bindingREST := &BindingREST{store: store}
 	return PodStorage{
@@ -109,6 +112,7 @@ func NewStorage(optsGetter generic.RESTOptionsGetter, k client.ConnectionInfoGet
 		Eviction:            newEvictionStorage(&statusStore, podDisruptionBudgetClient),
 		Status:              &StatusREST{store: &statusStore},
 		EphemeralContainers: &EphemeralContainersREST{store: &ephemeralContainersStore},
+		Resize:              &ResizeREST{store: &resizeStore},
 		Log:                 &podrest.LogREST{Store: store, KubeletConn: k},
 		Proxy:               &podrest.ProxyREST{Store: store, ProxyTransport: proxyTransport},
 		Exec:                &podrest.ExecREST{Store: store, KubeletConn: k},
@@ -365,3 +369,33 @@ func (r *EphemeralContainersREST) Update(ctx context.Context, name string, objIn
 	// subresources should never allow create on update.
 	return r.store.Update(ctx, name, objInfo, createValidation, updateValidation, false, options)
 }
+
+// ResizeREST implements the REST endpoint for resizing Pod containers.
+type ResizeREST struct {
+	store *genericregistry.Store
+}
+
+var _ = rest.Patcher(&ResizeREST{})
+
+// Get retrieves the object from the storage. It is required to support Patch.
+func (r *ResizeREST) Get(ctx context.Context, name string, options *metav1.GetOptions) (runtime.Object, error) {
+	return r.store.Get(ctx, name, options)
+}
+
+// New creates a new pod resource
+func (r *ResizeREST) New() runtime.Object {
+	return &api.Pod{}
+}
+
+// Destroy cleans up resources on shutdown.
+func (r *ResizeREST) Destroy() {
+	// Given that underlying store is shared with REST,
+	// we don't destroy it here explicitly.
+}
+
+// Update alters the resource fields in PodSpec
+func (r *ResizeREST) Update(ctx context.Context, name string, objInfo rest.UpdatedObjectInfo, createValidation rest.ValidateObjectFunc, updateValidation rest.ValidateObjectUpdateFunc, forceAllowCreate bool, options *metav1.UpdateOptions) (runtime.Object, bool, error) {
+	// We are explicitly setting forceAllowCreate to false in the call to the underlying storage because
+	// subresources should never allow create on update.
+	return r.store.Update(ctx, name, objInfo, createValidation, updateValidation, false, options)
+}

pkg/registry/core/pod/strategy.go

@@ -101,15 +101,6 @@ func (podStrategy) PrepareForUpdate(ctx context.Context, obj, old runtime.Object
 	newPod := obj.(*api.Pod)
 	oldPod := old.(*api.Pod)
 	newPod.Status = oldPod.Status
-
-	if utilfeature.DefaultFeatureGate.Enabled(features.InPlacePodVerticalScaling) {
-		// With support for in-place pod resizing, container resources are now mutable.
-		// If container resources are updated with new resource requests values, a pod resize is
-		// desired. The status of this request is reflected by setting Resize field to "Proposed"
-		// as a signal to the caller that the request is being considered.
-		podutil.MarkPodProposedForResize(oldPod, newPod)
-	}
-
 	podutil.DropDisabledPodFields(newPod, oldPod)
 }
 
@@ -286,6 +277,34 @@ func (podEphemeralContainersStrategy) WarningsOnUpdate(ctx context.Context, obj,
 	return nil
 }
 
+type podResizeStrategy struct {
+	podStrategy
+}
+
+// ResizeStrategy wraps and exports the used podStrategy for the storage package.
+var ResizeStrategy = podResizeStrategy{Strategy}
+
+func (podResizeStrategy) PrepareForUpdate(ctx context.Context, obj, old runtime.Object) {
+	newPod := obj.(*api.Pod)
+	oldPod := old.(*api.Pod)
+
+	podutil.MarkPodProposedForResize(oldPod, newPod)
+	podutil.DropDisabledPodFields(newPod, oldPod)
+}
+
+func (podResizeStrategy) ValidateUpdate(ctx context.Context, obj, old runtime.Object) field.ErrorList {
+	newPod := obj.(*api.Pod)
+	oldPod := old.(*api.Pod)
+	opts := podutil.GetValidationOptionsFromPodSpecAndMeta(&newPod.Spec, &oldPod.Spec, &newPod.ObjectMeta, &oldPod.ObjectMeta)
+	opts.ResourceIsPod = true
+	return nil 
+}
+
+// WarningsOnUpdate returns warnings for the given update.
+func (podResizeStrategy) WarningsOnUpdate(ctx context.Context, obj, old runtime.Object) []string {
+	return nil
+}
+
 // GetAttrs returns labels and fields of a given object for filtering purposes.
 func GetAttrs(obj runtime.Object) (labels.Set, fields.Set, error) {
 	pod, ok := obj.(*api.Pod)

pkg/registry/core/rest/storage_core.go

@@ -242,6 +242,9 @@ func (p *legacyProvider) NewRESTStorage(apiResourceConfigSource serverstorage.AP
 			storage[resource+"/eviction"] = podStorage.Eviction
 		}
 		storage[resource+"/ephemeralcontainers"] = podStorage.EphemeralContainers
+		if utilfeature.DefaultFeatureGate.Enabled(features.InPlacePodVerticalScaling) {
+			storage[resource+"/resize"] = podStorage.Resize
+		}
 	}
 	if resource := "bindings"; apiResourceConfigSource.ResourceEnabled(corev1.SchemeGroupVersion.WithResource(resource)) {
 		storage[resource] = podStorage.LegacyBinding