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Kubernetes - Custom Resource Definition(CRD)

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• Kubernetes - Custom Resource Definition(CRD)
  • Custom Resource Definition(CRD)
  • Custom Controller
  • Operator Framework
    • Imperative Commands
  • Lab: Create CRD

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Custom Resource Definition(CRD)

• custom resource
• custom controller

• CRD

• Example: CRD

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: flighttickets.com
spec:
  # if a namespaced object
  scope: Namespaced
  # group in the apiVersion section
  group: flight.com
  names:
    # resouce kind
    kind: FlightTicket
    # singular name
    singular: flightticket
    # plural name; used by API server, e.g., k api-resources
    plural: flightticket
    # short version name:
    shortNames:
      - ft
  versions:
    # version name in the apiVersion section
    - name: v1
      served: true
      storage: true
      # the parameters can be define in the spec section
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                from:
                  type: string
                to:
                  type: string
                number:
                  type: integer
                  minimum: 1
                  maximum: 10
      selectableFields:
        - jsonPath: .spec.from
        - jsonPath: .spec.to
        - jsonPath: .spec.number
      additionalPrinterColumns:
        - jsonPath: .spec.from
          name: From
          type: string
        - jsonPath: .spec.to
          name: To
          type: string
        - jsonPath: .spec.number
          name: Number
          type: integer

• Example of creating a flight ticket object

apiVersion: flights.com/v1
kind: FlightTicket
metadata:
  name: my-ticket
spec:
  from: London
  to: Paris
  number: 2

• can be managed
  • get, delete, describe

---

Custom Controller

• role
  • monitor the data in ETCD
  • implement based on the data change
• code in go

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Operator Framework

• used to pack both crd and custom controller
• OperatorHub.io

---

Imperative Commands

CMD	DESC
kubectl get crd	List crd

---

Lab: Create CRD

# crd-crontab.yaml
apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: crontabs.stable.example.com
spec:
  group: stable.example.com
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                cronSpec:
                  type: string
                image:
                  type: string
                replicas:
                  type: integer
  scope: Namespaced
  names:
    plural: crontabs
    singular: crontab
    kind: CronTab
    shortNames:
      - ct

kubectl apply -f crd-crontab.yaml
# customresourcedefinition.apiextensions.k8s.io/crontabs.stable.example.com created

kubectl get crd
# NAME                          CREATED AT
# crontabs.stable.example.com   2026-01-16T03:22:35Z

# my-crontab.yaml
apiVersion: "stable.example.com/v1"
kind: CronTab
metadata:
  name: my-new-cron-object
spec:
  cronSpec: "* * * * */5"
  image: my-awesome-cron-image
  replicas: 3

kubectl apply -f my-crontab.yaml
# crontab.stable.example.com/my-new-cron-object created

kubectl get ct
# NAME                 AGE
# my-new-cron-object   48s