Scenario

You need to extend the Kubernetes API to support a proprietary resource type called "Widget". By defining a CustomResourceDefinition (CRD), you allow users to manage these widgets using standard kubectl commands just like Pods or Services.

Task

Create a CustomResourceDefinition named widgets.mycompany.io. Define the group as mycompany.io and the kind as Widget short name wd and with served:true storage:true parameters. Specify the scope as Namespaced and define a version named v1. Create a Custom Resource instance of this type named sample-widget in the extensions namespace. Verify that the API accepts the new resource and that you can list it.

Example

Initial State (Before):

$ kubectl get widgets
error: the server doesn't have a resource type "widgets"

Success State (After):

# The API now recognizes the type
$ kubectl get crd widgets.mycompany.io
NAME                   CREATED AT
widgets.mycompany.io   2024-01-01T12:00:00Z

# The instance exists
$ kubectl get widgets -n extensions
NAME            AGE
sample-widget   5s

Step 1: Create the CRD
Create a new file named crd.yaml .

nano crd.yaml

Define the schema that tells Kubernetes about the new resource.

# crd.yaml
apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: widgets.mycompany.io
spec:
  group: mycompany.io
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
  scope: Namespaced
  names:
    plural: widgets
    singular: widget
    kind: Widget
    shortNames:
    - wd

Apply the configuration:

kubectl apply -f crd.yaml
# Expected Output:
# customresourcedefinition.apiextensions.k8s.io/widgets.mycompany.io created

Step 2: Create the Custom Resource

Once the CRD is established, create an instance of it.

Create a file named widget.yaml to define an instance of your new resource.

nano widget.yaml

# widget.yaml
apiVersion: mycompany.io/v1
kind: Widget
metadata:
  name: sample-widget
  namespace: extensions

Apply the instance:

kubectl apply -f widget.yaml
# Expected Output:
# widget.mycompany.io/sample-widget created

Note: If you get an error saying "no matches for kind", wait a few seconds for the CRD to register and try again.

Step 3: Verify

Check that the API server can now list your new resource type.

kubectl get widgets -n extensions
# Expected Output:
# NAME            AGE
# sample-widget   10s