Custom resources concept in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of a Custom Resource in Kubernetes?

In Kubernetes, what is the main reason to create a Custom Resource?

A To create a new namespace automatically for each deployment

B To replace the Kubernetes API server with a custom implementation

C To extend Kubernetes with new object types beyond built-in resources

D To manage user authentication and authorization

💡 Hint

Think about how Kubernetes can be customized to manage new kinds of objects.

Custom Resources allow users to add new types of objects to Kubernetes, enabling management of resources not originally included.

💻 Command Output

intermediate

Output of listing Custom Resource Definitions

What is the output of the command kubectl get crd in a Kubernetes cluster with two Custom Resource Definitions named widgets.example.com and gadgets.example.com?

Kubernetes

kubectl get crd

A

NAME                   STATUS
widgets.example.com     Active
gadgets.example.com     Active

B

NAME                   CREATED AT
widgets.example.com     2024-01-01T12:00:00Z
gadgets.example.com     2024-01-02T12:00:00Z

C No resources found in default namespace.

D Error from server (NotFound): customresourcedefinitions.apiextensions.k8s.io not found

💡 Hint

Think about what kubectl get crd lists and the typical columns shown.

The command lists all Custom Resource Definitions with their names and creation timestamps.

❓ Configuration

advanced

Correct YAML for defining a Custom Resource Definition

Which YAML snippet correctly defines a Custom Resource Definition (CRD) for a resource named widgets in group example.com with version v1?

A

apiVersion: apiextensions.k8s.io/v1beta1
kind: CustomResourceDefinition
metadata:
  name: widgets.example.com
spec:
  group: example.com
  versions:
  - name: v1
    served: true
    storage: true
  scope: Namespaced
  names:
    plural: widgets
    kind: Widget

B

apiVersion: v1
kind: CustomResourceDefinition
metadata:
  name: widgets.example.com
spec:
  group: example.com
  version: v1
  scope: Cluster
  names:
    plural: widgets
    kind: Widget

C

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: widgets
spec:
  group: example.com
  versions:
  - name: v1
    served: false
    storage: true
  scope: Namespaced
  names:
    plural: widgets
    kind: Widget

D

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: widgets.example.com
spec:
  group: example.com
  versions:
  - name: v1
    served: true
    storage: true
  scope: Namespaced
  names:
    plural: widgets
    singular: widget
    kind: Widget
    shortNames:
    - wdg

💡 Hint

Check the API version and the structure of the spec section for CRDs.

Option D uses the correct API version apiextensions.k8s.io/v1 and properly defines the versions list with served and storage fields.

🔀 Workflow

advanced

Order of steps to create and use a Custom Resource

Arrange the steps in the correct order to create and use a Custom Resource in Kubernetes.

A 1,3,2,4

B 3,1,2,4

C 1,2,3,4

D 2,1,3,4

💡 Hint

Think about registering the CRD before creating resources and verifying registration before usage.

First define and apply the CRD, then verify it is registered, next create resource instances, and finally manage them.

❓ Troubleshoot

expert

Reason for 'no matches for kind' error when applying a Custom Resource

You applied a Custom Resource YAML manifest but got the error: error: unable to recognize "widget.yaml": no matches for kind "Widget" in version "example.com/v1". What is the most likely cause?

A The Custom Resource Definition (CRD) for kind Widget is not installed or not yet registered in the cluster.

B The user does not have permission to create Custom Resources.

C The Kubernetes API server is down and cannot process the request.

D The YAML manifest has a syntax error in the spec section of the Custom Resource.

💡 Hint

Consider whether the cluster knows about the new resource kind before you create instances.

This error usually means the CRD is missing or not yet active, so Kubernetes does not recognize the resource kind.