Custom Resources

Custom Resource Definition

Let us define a CRD (custom resource definition) for our object:

crd.yaml

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: ephemeralvolumeclaims.kopf.dev
spec:
  scope: Namespaced
  group: kopf.dev
  names:
    kind: EphemeralVolumeClaim
    plural: ephemeralvolumeclaims
    singular: ephemeralvolumeclaim
    shortNames:
      - evcs
      - evc
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              x-kubernetes-preserve-unknown-fields: true
            status:
              type: object
              x-kubernetes-preserve-unknown-fields: true

Note the short names: they can be used as the aliases on the command line, when getting a list or an object of that kind.

And apply the definition to the cluster:

kubectl apply -f crd.yaml

If you want to revert this operation (e.g., to try it again):

kubectl delete crd ephemeralvolumeclaims.kopf.dev
kubectl delete -f crd.yaml

Custom Resource Objects

Now, we can already create the objects of this kind, apply it to the cluster, modify and delete them. Nothing will happen, since there is no implemented logic behind the objects yet.

Let’s make a sample object:

obj.yaml

apiVersion: kopf.dev/v1
kind: EphemeralVolumeClaim
metadata:
  name: my-claim

This is the minimal yaml file needed, with no spec or fields inside. We will add them later.

Apply it to the cluster:

kubectl apply -f obj.yaml

Get a list of the existing objects of this kind with one of the commands:

kubectl get EphemeralVolumeClaim
kubectl get ephemeralvolumeclaims
kubectl get ephemeralvolumeclaim
kubectl get evcs
kubectl get evc

Please note that we can use the short names as specified on the custom resource definition.