Custom Resource Definitions (CRDs) in Kubernetes - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary purpose of a Custom Resource Definition (CRD) in Kubernetes?

Choose the best description of what a CRD does in a Kubernetes cluster.

A It allows users to define new resource types that behave like built-in Kubernetes objects.

B It automatically scales pods based on CPU usage.

C It manages network policies between pods.

D It schedules pods to specific nodes based on resource availability.

💡 Hint

Think about how Kubernetes can be extended to manage new types of objects.

A CRD lets you create your own resource types so Kubernetes can understand and manage them like built-in objects such as pods or services.

💻 Command Output

intermediate

What is the output of this command after creating a CRD?

You run kubectl get crds after applying a CRD manifest named widgets.example.com. What will you see?

Kubernetes

kubectl get crds

A

NAME                  CREATED AT
widgets.example.com    2024-06-01T12:00:00Z

B No resources found in default namespace.

C Error from server (NotFound): crds "widgets.example.com" not found

D

NAME                  READY   STATUS    RESTARTS   AGE
widgets.example.com    True    Running   0          5m

💡 Hint

Remember that CRDs are cluster-wide resources, not namespace-scoped.

The kubectl get crds command lists all CRDs in the cluster with their names and creation timestamps.

❓ Configuration

advanced

Identify the error in this CRD manifest snippet

Review this CRD YAML snippet and select the option that correctly identifies the error.

Kubernetes

apiVersion: apiextensions.k8s.io/v1
kind: CustomResourceDefinition
metadata:
  name: gadgets.example.com
spec:
  group: example.com
  versions:
    - name: v1
      served: true
      storage: true
      schema:
        openAPIV3Schema:
          type: object
          properties:
            spec:
              type: object
              properties:
                size:
                  type: integer
  scope: Namespaced
  names:
    plural: gadgets
    singular: gadget
    kind: Gadget
    listKind: GadgetList

A The 'versions' list is missing the 'subresources' field, which is mandatory.

B The 'schema' field should be 'schema.openAPIV3Schema' under 'versions', but here it is correct.

C The 'metadata.name' must be the plural form plus the group, which is correct here.

D The 'scope' field value 'Namespaced' is invalid; it should be lowercase 'namespaced'.

💡 Hint

Check the indentation and field names carefully under 'versions'.

The 'schema' field is correctly named 'schema.openAPIV3Schema' under 'versions'. The other options contain incorrect claims: 'scope' is case-sensitive and must be 'Namespaced' with uppercase N; 'metadata.name' is correct; 'subresources' is optional.

❓ Troubleshoot

advanced

Why does this CRD fail to create?

You apply a CRD manifest but get the error: error: unable to recognize "crd.yaml": no matches for kind "CustomResourceDefinition" in version "apiextensions.k8s.io/v1beta1". What is the cause?

A The 'kind' field should be 'CustomResource' instead of 'CustomResourceDefinition'.

B The CRD manifest is missing the 'metadata' section.

C The API version 'apiextensions.k8s.io/v1beta1' is deprecated and no longer supported in recent Kubernetes versions.

D The Kubernetes cluster does not have the CRD controller installed.

💡 Hint

Check the API version compatibility with your Kubernetes cluster version.

The 'apiextensions.k8s.io/v1beta1' API version for CRDs was removed in Kubernetes 1.22+. You must use 'apiextensions.k8s.io/v1' instead.

🔀 Workflow

expert

Order the steps to create and use a new CRD in Kubernetes

Put these steps in the correct order to successfully create and use a new Custom Resource Definition.

A 2,1,3,4

B 3,1,2,4

C 1,3,2,4

D 1,2,3,4

💡 Hint

You must define and register the CRD before creating custom resources.

First, write the CRD manifest, then apply it to register the new resource type. After that, create instances of the custom resource and finally verify them.