CKA

Exercise

Create a CustomResourceDefinition named applications.company.com that defines an Application resource with the following properties:
- Group: company.com
- Kind: Application
- Plural: applications
- Singular: application
- Short names: app, apps
- Scope: Namespaced
The Application CRD should have a schema with these fields under spec:
- name (string, required)
- version (string, required)
- replicas (integer, minimum: 1, maximum: 10)
Apply the CRD to your cluster and verify it’s been created
Check that Kubernetes recognizes the new Application resource type
Create an Application resource named webapp with the following specifications:
- name: “my-web-app”
- version: “1.2.0”
- replicas: 3
List all Application resources and get the details of the webapp resource
Update the webapp resource to change the version to “1.3.0”
Delete the Application resource and the CRD

Documentation

https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/custom-resources/

Solution

Create a CustomResourceDefinition named applications.company.com

This CRD is defined in the following specification.

application-crd.yaml

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: applications.company.com
spec:
  group: company.com
  scope: Namespaced
  names:
    kind: Application
    plural: applications
    singular: application
    shortNames:
    - app
    - apps
  versions:
  - name: v1
    served: true
    storage: true
    schema:
      openAPIV3Schema:
        type: object
        properties:
          spec:
            type: object
            required:
            - name
            - version
            properties:
              name:
                type: string
              version:
                type: string
              replicas:
                type: integer
                minimum: 1
                maximum: 10

2-3. Apply the CRD to your cluster and verify it’s been created

kubectl apply -f application-crd.yaml
kubectl get crd applications.company.com

Check that Kubernetes recognizes the new Application resource type

$ k api-resources | grep application
applications                        app,apps     company.com/v1                      true         Application

Create an Application resource named webapp

Create the following specification:

webapp.yaml

apiVersion: company.com/v1
kind: Application
metadata:
  name: webapp
spec:
  name: "my-web-app"
  version: "1.2.0"
  replicas: 3

Apply it:

$ kubectl apply -f webapp.yaml
application.company.com/webapp created

List all Application resources and get the details of the webapp resource

kubectl get applications
kubectl get application webapp -o yaml

You can also use the shortname app as defined in the CRD.:

kubectl get apps
kubectl describe app webapp

Update the webapp resource to change the version to “1.3.0”

kubectl patch application webapp --type='merge' -p='{"spec":{"version":"1.3.0"}}'

Or you can edit directly:

kubectl edit application webapp

Then, verify the change is taken into account:

kubectl get application webapp -o yaml

Delete the Application resource and the CRD

kubectl delete application webapp
kubectl delete crd applications.company.com