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How to Generate Scaffold CRDs

Explore how to generate scaffold CustomResourceDefinitions (CRDs) to extend Kubernetes APIs. Learn the step-by-step process to create, define, and install scaffold projects, automate manifest generation, and manage custom resources effectively within your cluster.

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Scaffold CRDs

With CRDs, we can easily extend Kubernetes APIs by declaring objects in the YAML or JSON format.

Now, let’s take a look at the CRD and schema in more detail, so we can learn how to make a scaffold CRD with our own definitions.

CRD schema

The schema of CRDs is shown below:

YAML
apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  # name must be in the form: <plural>.<group>
  name: <name>
spec:
  group: <group name>
  conversion: #optional
    # Specifies how custom resources are converted between versions
    # can be None or Webhook
    strategy: None
  names: # Specify the resource and kind names for the custom resource
    categories: # optional
    # List of categories this custom resource belongs to (e.g. 'all')
    - <mycategory>
    kind: <Uppercase name>
    listKind: <Uppercase list kind, defaulted to be kindList>
    plural: <lowercase plural name>
    shortNames: # optional
    # List of strings as short names
    - <alias1>
    singular: <lowercase singular name, defaulted to be lowercase kind>
  scope: Namespaced  # Namespaced or cluster scope
  versions: # List of all API versions
  - name: v1alpha1
    schema: # Optional
      openAPIV3Schema: # OpenAPI v3 schema to use for validation and pruning
        description: HelmChart is the Schema for the helm chart
        properties: # Describe all the fields
          ...
        required: # Mark required fields
        - ...
        type: object
    served: true
    storage: true
    subresources: # Optional
      status: {} # To enable the status subresource (optional)
      scale: # Optional
        specReplicasPath: <JSON path for the replica field, such as `spec.replicas`>
        statusReplicasPath: <JSON path for the replica number in the status>
        labelSelectorPath: <JSON path that corresponds to Scale `status.selector`>
    additionalPrinterColumns: # Optional
    # Specify additional columns returned in Table output. Used by kubectl
    - description: The phase of this custom resource # Example
      jsonPath: .status.phase
      name: STATUS
      type: string
    - jsonPath: .metadata.creationTimestamp # Example
      name: AGE
      type: date

Defining a simple API can be quite easy because we’ve only got a few fields. However, creating OpenAPI schema manually can be very tedious, because we have to we declare all the fields, including ...