Create HierarchicalNamespace CRD

This CRD is created as the UX of the HNC self-service namespace. See
design at http://bit.ly/hnc-self-serve-ux.

Tested on a GKE cluster by "kubectl apply -f" the generated CRD yaml
file. The CRD was created with success.

incubator/hnc/api/v1alpha1/hierarchical_namespace.go

@@ -0,0 +1,78 @@
+/*
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package v1alpha1
+
+import (
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+)
+
+// HNSState describes the state of a hierarchical namespace. The state could be
+// "missing", "ok" or "conflict". The definitions will be described below.
+type HNSState string
+
+// HNSStates, which are documented in the comment to HierarchicalNamespaceStatus.State.
+const (
+	// Missing means the child namespace has not been created yet. This should be the default
+	// state when the HNS is just created.
+	Missing HNSState = "missing"
+
+	// Ok means the child namespace exists.
+	Ok HNSState = "ok"
+
+	// Conflict means a namespace of the same name already exists.
+	Conflict HNSState = "conflict"
+)
+
+// HierarchicalNamespaceStatus defines the observed state of HierarchicalNamespace.
+type HierarchicalNamespaceStatus struct {
+	// Describes the state of a hierarchical namespace.
+	//
+	// Currently, the supported values are:
+	//
+	// - "missing": the child namespace has not been created yet. This should be the default
+	// state when the HNS is just created.
+	//
+	// - "ok": the child namespace exists.
+	//
+	// - "conflict": a namespace of the same name already exists. If the validation webhook
+	// works properly, this should never happen since the HNS won't be created at the first place.
+	State HNSState `json:"status,omitempty"`
+}
+
+// +kubebuilder:object:root=true
+// +kubebuilder:resource:path=hierarchicalnamespaces,shortName=hns,scope=Namespaced
+
+// HierarchicalNamespace is the Schema for the self-service namespace API.
+// See details at http://bit.ly/hnc-self-serve-ux.
+type HierarchicalNamespace struct {
+	metav1.TypeMeta   `json:",inline"`
+	metav1.ObjectMeta `json:"metadata,omitempty"`
+
+	Status HierarchicalNamespaceStatus `json:"status,omitempty"`
+}
+
+// +kubebuilder:object:root=true
+
+// HierarchicalNamespaceList contains a list of HierarchicalNamespace.
+type HierarchicalNamespaceList struct {
+	metav1.TypeMeta `json:",inline"`
+	metav1.ListMeta `json:"metadata,omitempty"`
+	Items           []HierarchicalNamespace `json:"items"`
+}
+
+func init() {
+	SchemeBuilder.Register(&HierarchicalNamespace{}, &HierarchicalNamespaceList{})
+}

incubator/hnc/config/crd/bases/hnc.x-k8s.io_hierarchicalnamespaces.yaml

@@ -0,0 +1,61 @@
+
+---
+apiVersion: apiextensions.k8s.io/v1beta1
+kind: CustomResourceDefinition
+metadata:
+  annotations:
+    controller-gen.kubebuilder.io/version: v0.2.4
+  creationTimestamp: null
+  name: hierarchicalnamespaces.hnc.x-k8s.io
+spec:
+  group: hnc.x-k8s.io
+  names:
+    kind: HierarchicalNamespace
+    listKind: HierarchicalNamespaceList
+    plural: hierarchicalnamespaces
+    shortNames:
+    - hns
+    singular: hierarchicalnamespace
+  scope: Namespaced
+  validation:
+    openAPIV3Schema:
+      description: HierarchicalNamespace is the Schema for the self-service namespace
+        API. See details at http://bit.ly/hnc-self-serve-ux.
+      properties:
+        apiVersion:
+          description: 'APIVersion defines the versioned schema of this representation
+            of an object. Servers should convert recognized schemas to the latest
+            internal value, and may reject unrecognized values. More info: https://git.k8s.io/community/contributors/devel/api-conventions.md#resources'
+          type: string
+        kind:
+          description: 'Kind is a string value representing the REST resource this
+            object represents. Servers may infer this from the endpoint the client
+            submits requests to. Cannot be updated. In CamelCase. More info: https://git.k8s.io/community/contributors/devel/api-conventions.md#types-kinds'
+          type: string
+        metadata:
+          type: object
+        status:
+          description: HierarchicalNamespaceStatus defines the observed state of HierarchicalNamespace.
+          properties:
+            status:
+              description: "Describes the state of a hierarchical namespace. \n Currently,
+                the supported values are: \n - \"missing\": the child namespace has
+                not been created yet. This should be the default state when the HNS
+                is just created. \n - \"ok\": the child namespace exists. \n - \"conflict\":
+                a namespace of the same name already exists. If the validation webhook
+                works properly, this should never happen since the HNS won't be created
+                at the first place."
+              type: string
+          type: object
+      type: object
+  version: v1alpha1
+  versions:
+  - name: v1alpha1
+    served: true
+    storage: true
+status:
+  acceptedNames:
+    kind: ""
+    plural: ""
+  conditions: []
+  storedVersions: []