Custom Resource Definitions (CRDs) in Kubernetes

To install Custom Resource Definitions (CRDs) in Kubernetes, you typically define them in a YAML file and then apply that file using kubectl. CRDs allow you to extend the Kubernetes API by defining your own resources.

Here’s a step-by-step guide to install CRDs:

Step 1: Create a CRD YAML File

Create a YAML file that defines your CRD. Below is an example of a CRD YAML definition for a MyCustomResource:

 

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: mycustomresources.mygroup.example.com
spec:
  group: mygroup.example.com
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                someField:
                  type: string
  scope: Namespaced
  names:
    plural: mycustomresources
    singular: mycustomresource
    kind: MyCustomResource
    shortNames:
      - mcr

This defines a CRD called MyCustomResource, which is scoped to a namespace and has a field someField.

Step 2: Install the CRD using kubectl

Once you’ve defined your CRD YAML file, you can install it using the kubectl command. Assuming the file is called mycustomresource-crd.yaml, you can install it like this:

kubectl apply -f mycustomresource-crd.yaml
 

Step 3: Verify the CRD is Installed

To verify the CRD has been installed successfully, you can use:

kubectl get crds

 You should see mycustomresources.mygroup.example.com in the list of CRDs.

Step 4: Create Custom Resources

Once the CRD is installed, you can now create Custom Resources (CRs) based on that CRD. Here’s an example of a custom resource using the CRD:

apiVersion: mygroup.example.com/v1
kind: MyCustomResource
metadata:
  name: my-custom-resource-instance
spec:
  someField: "Some value"

To create this custom resource, save the YAML to a file (e.g., my-custom-resource.yaml) and apply it:

 kubectl apply -f my-custom-resource.yaml