Allow CRD /scale labelSelectors to be under either status or spec (#78234)

* apiextensions API doc: allow labelSelectorPath to be under .status or .spec

* apiextensions validation: allow labelSelectorPath to be under .status or .spec

* test

* generated

api/openapi-spec/swagger.json

@@ -16616,7 +16616,7 @@
       "description": "CustomResourceSubresourceScale defines how to serve the scale subresource for CustomResources.",
       "properties": {
         "labelSelectorPath": {
-          "description": "LabelSelectorPath defines the JSON path inside of a CustomResource that corresponds to Scale.Status.Selector. Only JSON paths without the array notation are allowed. Must be a JSON Path under .status. Must be set to work with HPA. If there is no value under the given path in the CustomResource, the status label selector value in the /scale subresource will default to the empty string.",
+          "description": "LabelSelectorPath defines the JSON path inside of a CustomResource that corresponds to Scale.Status.Selector. Only JSON paths without the array notation are allowed. Must be a JSON Path under .status or .spec. Must be set to work with HPA. The field pointed by this JSON path must be a string field (not a complex selector struct) which contains a serialized label selector in string form. More info: https://kubernetes.io/docs/tasks/access-kubernetes-api/custom-resources/custom-resource-definitions#scale-subresource If there is no value under the given path in the CustomResource, the status label selector value in the /scale subresource will default to the empty string.",
           "type": "string"
         },
         "specReplicasPath": {

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/types.go

@@ -393,8 +393,11 @@ type CustomResourceSubresourceScale struct {
 	StatusReplicasPath string
 	// LabelSelectorPath defines the JSON path inside of a CustomResource that corresponds to Scale.Status.Selector.
 	// Only JSON paths without the array notation are allowed.
-	// Must be a JSON Path under .status.
+	// Must be a JSON Path under .status or .spec.
 	// Must be set to work with HPA.
+	// The field pointed by this JSON path must be a string field (not a complex selector struct)
+	// which contains a serialized label selector in string form.
+	// More info: https://kubernetes.io/docs/tasks/access-kubernetes-api/custom-resources/custom-resource-definitions#scale-subresource
 	// If there is no value under the given path in the CustomResource, the status label selector value in the /scale
 	// subresource will default to the empty string.
 	// +optional

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/generated.proto

@@ -327,8 +327,11 @@ message CustomResourceSubresourceScale {
 
   // LabelSelectorPath defines the JSON path inside of a CustomResource that corresponds to Scale.Status.Selector.
   // Only JSON paths without the array notation are allowed.
-  // Must be a JSON Path under .status.
+  // Must be a JSON Path under .status or .spec.
   // Must be set to work with HPA.
+  // The field pointed by this JSON path must be a string field (not a complex selector struct)
+  // which contains a serialized label selector in string form.
+  // More info: https://kubernetes.io/docs/tasks/access-kubernetes-api/custom-resources/custom-resource-definitions#scale-subresource
   // If there is no value under the given path in the CustomResource, the status label selector value in the /scale
   // subresource will default to the empty string.
   // +optional

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/v1beta1/types.go

@@ -412,8 +412,11 @@ type CustomResourceSubresourceScale struct {
 	StatusReplicasPath string `json:"statusReplicasPath" protobuf:"bytes,2,opt,name=statusReplicasPath"`
 	// LabelSelectorPath defines the JSON path inside of a CustomResource that corresponds to Scale.Status.Selector.
 	// Only JSON paths without the array notation are allowed.
-	// Must be a JSON Path under .status.
+	// Must be a JSON Path under .status or .spec.
 	// Must be set to work with HPA.
+	// The field pointed by this JSON path must be a string field (not a complex selector struct)
+	// which contains a serialized label selector in string form.
+	// More info: https://kubernetes.io/docs/tasks/access-kubernetes-api/custom-resources/custom-resource-definitions#scale-subresource
 	// If there is no value under the given path in the CustomResource, the status label selector value in the /scale
 	// subresource will default to the empty string.
 	// +optional

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation.go

@@ -794,8 +794,8 @@ func ValidateCustomResourceDefinitionSubresources(subresources *apiextensions.Cu
 		if subresources.Scale.LabelSelectorPath != nil && len(*subresources.Scale.LabelSelectorPath) > 0 {
 			if errs := validateSimpleJSONPath(*subresources.Scale.LabelSelectorPath, fldPath.Child("scale.labelSelectorPath")); len(errs) > 0 {
 				allErrs = append(allErrs, errs...)
-			} else if !strings.HasPrefix(*subresources.Scale.LabelSelectorPath, ".status.") {
+			} else if !strings.HasPrefix(*subresources.Scale.LabelSelectorPath, ".spec.") && !strings.HasPrefix(*subresources.Scale.LabelSelectorPath, ".status.") {
-				allErrs = append(allErrs, field.Invalid(fldPath.Child("scale.labelSelectorPath"), subresources.Scale.LabelSelectorPath, "should be a json path under .status"))
+				allErrs = append(allErrs, field.Invalid(fldPath.Child("scale.labelSelectorPath"), subresources.Scale.LabelSelectorPath, "should be a json path under either .spec or .status"))
 			}
 		}
 	}

staging/src/k8s.io/apiextensions-apiserver/pkg/apis/apiextensions/validation/validation_test.go

@@ -1162,6 +1162,83 @@ func TestValidateCustomResourceDefinition(t *testing.T) {
 				required("spec", "versions[1]", "schema", "openAPIV3Schema"),
 			},
 		},
+		{
+			name: "labelSelectorPath outside of .spec and .status",
+			resource: &apiextensions.CustomResourceDefinition{
+				ObjectMeta: metav1.ObjectMeta{Name: "plural.group.com"},
+				Spec: apiextensions.CustomResourceDefinitionSpec{
+					Group:   "group.com",
+					Version: "version0",
+					Versions: []apiextensions.CustomResourceDefinitionVersion{
+						{
+							// null labelSelectorPath
+							Name:    "version0",
+							Served:  true,
+							Storage: true,
+							Subresources: &apiextensions.CustomResourceSubresources{
+								Scale: &apiextensions.CustomResourceSubresourceScale{
+									SpecReplicasPath:   ".spec.replicas",
+									StatusReplicasPath: ".status.replicas",
+								},
+							},
+						},
+						{
+							// labelSelectorPath under .status
+							Name:    "version1",
+							Served:  true,
+							Storage: false,
+							Subresources: &apiextensions.CustomResourceSubresources{
+								Scale: &apiextensions.CustomResourceSubresourceScale{
+									SpecReplicasPath:   ".spec.replicas",
+									StatusReplicasPath: ".status.replicas",
+									LabelSelectorPath:  strPtr(".status.labelSelector"),
+								},
+							},
+						},
+						{
+							// labelSelectorPath under .spec
+							Name:    "version2",
+							Served:  true,
+							Storage: false,
+							Subresources: &apiextensions.CustomResourceSubresources{
+								Scale: &apiextensions.CustomResourceSubresourceScale{
+									SpecReplicasPath:   ".spec.replicas",
+									StatusReplicasPath: ".status.replicas",
+									LabelSelectorPath:  strPtr(".spec.labelSelector"),
+								},
+							},
+						},
+						{
+							// labelSelectorPath outside of .spec and .status
+							Name:    "version3",
+							Served:  true,
+							Storage: false,
+							Subresources: &apiextensions.CustomResourceSubresources{
+								Scale: &apiextensions.CustomResourceSubresourceScale{
+									SpecReplicasPath:   ".spec.replicas",
+									StatusReplicasPath: ".status.replicas",
+									LabelSelectorPath:  strPtr(".labelSelector"),
+								},
+							},
+						},
+					},
+					Scope: apiextensions.NamespaceScoped,
+					Names: apiextensions.CustomResourceDefinitionNames{
+						Plural:   "plural",
+						Singular: "singular",
+						Kind:     "Plural",
+						ListKind: "PluralList",
+					},
+					PreserveUnknownFields: pointer.BoolPtr(true),
+				},
+				Status: apiextensions.CustomResourceDefinitionStatus{
+					StoredVersions: []string{"version0"},
+				},
+			},
+			errors: []validationMatch{
+				invalid("spec", "versions[3]", "subresources", "scale", "labelSelectorPath"),
+			},
+		},
 	}
 
 	for _, tc := range tests {