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Lab 6.3 - StorageClasses and Dynamic Provisioning

Lab Objectives​

By the end of this lab, you will be able to:

  • Understand the StorageClass concept.
  • Create a custom StorageClass.
  • Use dynamic provisioning with a PVC.
  • Understand the different provisioner types.
  • Verify automatic PV provisioning.

Estimated Duration​

45-60 minutes

Prerequisites​

  • kubectl installed and configured.
  • Functional local Kubernetes cluster (minikube or kind).
  • Knowledge of StorageClasses (Chapter 6.3).

Part 1: Understanding StorageClasses​

A StorageClass defines a "type" of storage with characteristics (provisioner, parameters, reclaim policy). It enables dynamic provisioning of PersistentVolumes.

Step 1.1: List Existing StorageClasses​

Check the StorageClasses available in your cluster:

kubectl get storageclass
# or
kubectl get sc

On minikube, you should see a default StorageClass (e.g., standard or hostpath). On kind, there may be standard or none.

Check the details of a StorageClass:

kubectl describe storageclass <storageclass-name>

Part 2: Creating a Custom StorageClass​

For a local cluster, we will create a StorageClass that uses hostPath as a provisioner (via a local or manual provisioner).

Step 2.1: Create a StorageClass​

Create a file storageclass-local.yaml:

# storageclass-local.yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner # No automatic provisioning for hostPath
volumeBindingMode: WaitForFirstConsumer # Wait for a Pod to use the PVC before creating the PV
allowVolumeExpansion: false # Does not allow volume expansion

Explanation:

  • provisioner: kubernetes.io/no-provisioner: Indicates there is no automatic provisioning. For a local cluster with hostPath, we must create PVs manually, but the StorageClass allows grouping them.
  • volumeBindingMode: WaitForFirstConsumer: The PVC waits for a Pod to be created before binding the PV. This allows the scheduler to choose the right node.
  • allowVolumeExpansion: false: Volumes cannot be expanded after creation.

Apply the StorageClass:

kubectl apply -f storageclass-local.yaml

Verify it is created:

kubectl get storageclass local-storage

Part 3: Dynamic Provisioning (Simulation)​

For true dynamic provisioning, you would need a provisioner like:

  • kubernetes.io/aws-ebs (AWS)
  • kubernetes.io/azure-disk (Azure)
  • kubernetes.io/gce-pd (GCP)
  • kubernetes.io/cinder (OpenStack)

On minikube, you can use the k8s.io/minikube-hostpath provisioner if available.

Step 3.1: Create a StorageClass with Dynamic Provisioning (minikube)​

If using minikube, create a StorageClass that uses the minikube provisioner:

# storageclass-minikube.yaml
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: minikube-dynamic
provisioner: k8s.io/minikube-hostpath # Minikube provisioner
volumeBindingMode: Immediate # Bind immediately
reclaimPolicy: Delete # Delete the PV when the PVC is deleted
allowVolumeExpansion: true # Allow expansion

Apply it:

kubectl apply -f storageclass-minikube.yaml

Step 3.2: Create a PVC with the StorageClass​

Create a file pvc-dynamic.yaml:

# pvc-dynamic.yaml
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-dynamic
spec:
  storageClassName: minikube-dynamic # Uses the StorageClass with dynamic provisioning
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 100Mi

Apply the PVC:

kubectl apply -f pvc-dynamic.yaml

Verify the PVC is created and a PV has been automatically provisioned:

kubectl get pvc pvc-dynamic
kubectl get pv

You should see a new PV automatically created with status Bound and linked to the PVC.

Part 4: Using the Dynamic PVC​

Create a Pod that uses the dynamic PVC:

# pod-dynamic-pvc.yaml
apiVersion: v1
kind: Pod
metadata:
  name: pod-dynamic-pvc
spec:
  containers:
  - name: app-container
    image: busybox
    command: ["/bin/sh", "-c"]
    args: ["echo 'Data in a dynamic volume - $(date)' > /data/dynamic-data.txt && cat /data/dynamic-data.txt && sleep 3600"]
    volumeMounts:
    - name: dynamic-storage
      mountPath: /data
  volumes:
  - name: dynamic-storage
    persistentVolumeClaim:
      claimName: pvc-dynamic

Apply the Pod:

kubectl apply -f pod-dynamic-pvc.yaml

Check the logs:

kubectl logs pod-dynamic-pvc

Part 5: Volume Expansion (Optional)​

If allowVolumeExpansion: true, you can expand a PVC after creation.

Modify the PVC to request more space:

kubectl patch pvc pvc-dynamic -p '{"spec":{"resources":{"requests":{"storage":"200Mi"}}}}'

Verify the request was updated:

kubectl get pvc pvc-dynamic

Note: Actual volume expansion depends on the provisioner and the underlying storage type.

Part 6: Cleanup​

Delete the created resources:

kubectl delete pod pod-dynamic-pvc
kubectl delete -f pvc-dynamic.yaml
# The PV will be automatically deleted if reclaimPolicy: Delete
kubectl delete -f storageclass-minikube.yaml
kubectl delete -f storageclass-local.yaml

Lab Summary​

In this lab, you explored StorageClasses and dynamic provisioning. You learned to create custom StorageClasses, use automatic PV provisioning via PVCs, and understand the different binding modes and reclaim policies.

Next Steps​

The last lab in this module will show you how to use PersistentVolumes with StatefulSets for stateful applications.

Lab 6.4: StatefulSet with Persistent Storage

Lab created: December 2024