Can you explain what CRD means in the context of Kubernetes?

CRD (Custom Resource Definition) in Kubernetes is a mechanism that allows you to create your own resources (objects) in the cluster, extending the standard Kubernetes API. With CRD, you can define a new resource type with specific fields and behaviors, to manage application-specific objects just like standard ones, such as Pod or Service.

Example of creating a CRD to add a new resource MyApp in the cluster:

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: myapps.example.com
spec:
  group: example.com
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                replicas:
                  type: integer
  scope: Namespaced
  names:
    plural: myapps
    singular: myapp
    kind: MyApp
    shortNames:
    - ma

After creating this CRD, you can create objects of type MyApp and manage them via kubectl and Kubernetes API.