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Chapter 6.3 - StorageClasses and Dynamic Provisioning

Learning Objectives​

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

  • Understand what a StorageClass is
  • Configure dynamic provisioning
  • Create and use StorageClasses
  • Understand the different provisioners
  • Choose the right StorageClass based on the use case
  • Configure volume expansion

Introduction​

Manually creating PersistentVolumes for each storage request is tedious. StorageClasses enable dynamic provisioning: Kubernetes automatically creates a PV when a PVC is created.

What Is a StorageClass?​

A StorageClass describes the available storage classes and enables dynamic provisioning of PersistentVolumes. It defines:

  • The provisioner (how to create the volume)
  • The parameters (storage type, IOPS, etc.)
  • The default reclaim policy
  • Whether volume expansion is allowed

Creating a StorageClass​

Example: AWS EBS StorageClass​

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast-ssd
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp3
  iops: "3000"
  throughput: "125"
reclaimPolicy: Delete
allowVolumeExpansion: true
volumeBindingMode: WaitForFirstConsumer

Components:

  • name: StorageClass name
  • provisioner: Plugin that creates the volume
  • parameters: Provisioner-specific parameters
  • reclaimPolicy: Retain or Delete (default)
  • allowVolumeExpansion: Allows volume resizing
  • volumeBindingMode: Immediate or WaitForFirstConsumer

Provisioners​

Cloud Provisioners​

AWS EBS​

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: aws-ebs-gp3
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp3
  iops: "3000"
  throughput: "125"
  encrypted: "true"
  kmsKeyId: "arn:aws:kms:..."

Azure Disk​

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: azure-disk-ssd
provisioner: kubernetes.io/azure-disk
parameters:
  storageaccounttype: Premium_LRS
  kind: managed

GCE Persistent Disk​

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: gce-pd-ssd
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-ssd
  replication-type: regional-pd

Local Provisioners​

Local Storage​

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: local-storage
provisioner: kubernetes.io/no-provisioner
volumeBindingMode: WaitForFirstConsumer

NFS​

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: nfs-storage
provisioner: example.com/nfs
parameters:
  server: nfs-server.example.com
  path: /exports

Dynamic Provisioning​

Create a PVC with StorageClass​

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-dynamic
spec:
  storageClassName: fast-ssd
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi

Process:

Result: Kubernetes automatically creates a PV matching the PVC.

Volume Binding Modes​

Immediate​

The PV is created and bound immediately when the PVC is created.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: immediate-sc
provisioner: kubernetes.io/aws-ebs
volumeBindingMode: Immediate

Advantages:

  • PVC available immediately
  • No waiting

Disadvantages:

  • Volume created even if unused
  • May create volumes on the wrong node

WaitForFirstConsumer​

The PV is created only when a Pod uses the PVC.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: wait-sc
provisioner: kubernetes.io/aws-ebs
volumeBindingMode: WaitForFirstConsumer

Advantages:

  • Volume created on the correct node
  • Avoids unused volumes

Disadvantages:

  • Delay on first mount

Volume Expansion​

Enable Expansion​

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: expandable-sc
provisioner: kubernetes.io/aws-ebs
allowVolumeExpansion: true

Expand a Volume​

  1. Modify the PVC to request more storage:
kubectl patch pvc pvc-dynamic -p '{"spec":{"resources":{"requests":{"storage":"20Gi"}}}}'
  1. Verify the expansion:
kubectl get pvc pvc-dynamic

Note: Expansion is supported only if:

  • allowVolumeExpansion: true in the StorageClass
  • The provisioner supports expansion
  • The filesystem supports expansion (ext4, xfs)

Complete Example​

Step 1: Create the StorageClass​

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: production-ssd
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp3
  iops: "3000"
  throughput: "125"
  encrypted: "true"
reclaimPolicy: Retain
allowVolumeExpansion: true
volumeBindingMode: WaitForFirstConsumer

Step 2: Create the PVC​

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: app-data-pvc
spec:
  storageClassName: production-ssd
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 50Gi

Step 3: Use in a Deployment​

apiVersion: apps/v1
kind: Deployment
metadata:
  name: app
spec:
  replicas: 3
  selector:
    matchLabels:
      app: myapp
  template:
    metadata:
      labels:
        app: myapp
    spec:
      containers:
      - name: app
        image: my-app:1.0
        volumeMounts:
        - name: data
          mountPath: /data
      volumes:
      - name: data
        persistentVolumeClaim:
          claimName: app-data-pvc

Default StorageClass​

Define a Default StorageClass​

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: default-storage
  annotations:
    storageclass.kubernetes.io/is-default-class: "true"
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp3

Result: PVCs without a storageClassName use this StorageClass.

PVC Without StorageClass​

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-default
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  # No storageClassName = uses the default StorageClass

Useful Commands​

View StorageClasses​

# List StorageClasses
kubectl get storageclass
kubectl get sc

# StorageClass details
kubectl describe storageclass fast-ssd

View PVCs and PVs​

# List PVCs
kubectl get pvc

# View dynamically created PVs
kubectl get pv

# PVC details
kubectl describe pvc pvc-dynamic

Volume Expansion​

# Expand a PVC
kubectl patch pvc pvc-dynamic -p '{"spec":{"resources":{"requests":{"storage":"20Gi"}}}}'

# Check status
kubectl get pvc pvc-dynamic

Best Practices​

1. Use Dynamic Provisioning​

Prefer StorageClasses over manual provisioning for flexibility.

2. Choose the Right Volume Binding Mode​

  • Immediate: For shared volumes (NFS)
  • WaitForFirstConsumer: For local volumes (EBS, Azure Disk)

3. Enable Expansion​

Enable allowVolumeExpansion: true to allow resizing without recreation.

4. Appropriate Reclaim Policy​

  • Retain: For important data
  • Delete: For temporary data

5. Monitoring​

Monitor storage usage and costs.

Summary​

In this chapter, you learned:

StorageClass: Describes storage classes and enables dynamic provisioning
Dynamic provisioning: Automatic PV creation when a PVC is created
Provisioners: Plugins that create volumes (EBS, Azure Disk, GCE PD, NFS, etc.)
Volume Binding Modes: Immediate (instant) or WaitForFirstConsumer (wait for Pod)
Expansion: Allows resizing an existing volume
Default StorageClass: Used when no storageClassName is specified
Advantages: Flexibility, automation, reduced manual management

Next Steps​

Chapter 6.4: StatefulSets with Persistent Storage
Lab 6.3: StorageClasses and Dynamic Provisioning

Chapter created: December 2024