Kubernetes Storage - The Dynamic Way | StorageClass & On-Demand Provisioning

Comprehensive guide to Kubernetes Dynamic Storage Provisioning covering StorageClass configuration, on-demand storage automation, reclaim policies (Delete, Retain), access modes (RWO, ROX, RWX), volume binding modes (Immediate, WaitForFirstConsumer), and automated Persistent Volume management

What is StorageClass?

StorageClass Definition

  • Describes the "classes" of storage offered by the admin
  • An abstraction on top of an external storage resource
  • No need to set a capacity in the StorageClass
  • Eliminates the need for the admin to pre-provision Persistent Volumes
  • Enables dynamic provisioning of storage

Key Benefits

Resource Efficiency

No wasted storage - volumes are created with exact requested size

Automation

Automatic PV creation when PVC is created

Flexibility

Multiple storage classes for different performance needs

PVC Created
→
StorageClass
→
Provisioner
→
PV Created
→
Pod Bound

How Dynamic Provisioning Works

  1. User creates a PVC referencing a StorageClass
  2. StorageClass triggers the provisioner to create storage
  3. Provisioner creates a PV with the requested specifications
  4. PVC automatically binds to the newly created PV
  5. Pod uses the PVC and gets access to the storage

StorageClass Configuration

Basic StorageClass Definition

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp2
  fsType: ext4
reclaimPolicy: Delete
volumeBindingMode: Immediate
allowVolumeExpansion: true

Configuration Parameters

Provisioner

Determines which volume plugin is used for provisioning PVs

kubernetes.io/aws-ebs
kubernetes.io/gce-pd
kubernetes.io/azure-disk

Parameters

Storage backend specific configuration

type: gp2, io1, st1 (AWS)
replication-type: regional-pd (GCP)
storageaccounttype: Premium_LRS (Azure)

Advanced StorageClass Examples

# AWS EBS with encryption
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: encrypted-fast
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp3
  fsType: ext4
  encrypted: "true"
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer
# NFS StorageClass
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: nfs-shared
provisioner: example.com/nfs
parameters:
  server: nfs-server.example.com
  path: /exports
reclaimPolicy: Retain
volumeBindingMode: Immediate

Access Modes

ReadWriteMany (RWX)

The volume can be mounted as read-write by many pods

ReadOnlyMany (ROX)

The volume can be mounted read-only by many pods

ReadWriteOnce (RWO)

The volume can be mounted as read-write by a single pod

Note: With ReadWriteOnce, the pod that mounts the volume first will be able to write to it. Other pods can mount it in read-only mode if the storage backend supports it.

Access Mode Support by Storage Backend

Storage Type RWO ROX RWX
AWS EBS
AWS EFS
NFS
Azure Disk

Reclaim Policies

Delete Policy

Delete the data upon PVC deletion

This is the default policy for dynamically provisioned volumes

reclaimPolicy: Delete

Retain Policy

Keeps the data upon PVC deletion

Manual cleanup required. Keeps data safe from accidental deletion.

reclaimPolicy: Retain

Delete Policy Behavior

  • Automatically deletes both PV and underlying storage
  • Ideal for temporary or reproducible data
  • Prevents storage resource leaks
  • Default for most cloud providers

Retain Policy Behavior

  • PV enters "Released" state when PVC is deleted
  • Underlying storage and data are preserved
  • Manual intervention required to reclaim
  • Ideal for critical or irreplaceable data

kubectl StorageClass Commands

Deploy StorageClass or PVC

kubectl apply -f [definition.yaml]

Create StorageClass and PVC resources from YAML files

Get StorageClass and PVC Lists

kubectl get sc
kubectl get pvc

List all StorageClasses and PersistentVolumeClaims

Describe StorageClass

kubectl describe sc [className]

Get detailed information about a StorageClass

Delete StorageClass and PVC

kubectl delete -f [definition.yaml]
kubectl delete sc [className]
kubectl delete pvc [pvcName]

Delete using YAML file or resource names

Complete Dynamic Provisioning Example

StorageClass Definition

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

PersistentVolumeClaim

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: app-data-pvc
  namespace: production
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: fast-ssd
  resources:
    requests:
      storage: 100Gi

Deployment Using the PVC

apiVersion: apps/v1
kind: Deployment
metadata:
  name: database-app
  namespace: production
spec:
  replicas: 1
  selector:
    matchLabels:
      app: database
  template:
    metadata:
      labels:
        app: database
    spec:
      containers:
      - name: database
        image: postgres:14
        volumeMounts:
        - name: data-storage
          mountPath: /var/lib/postgresql/data
        env:
        - name: POSTGRES_DB
          value: "mydatabase"
        - name: POSTGRES_USER
          value: "admin"
        - name: POSTGRES_PASSWORD
          valueFrom:
            secretKeyRef:
              name: db-secret
              key: password
      volumes:
      - name: data-storage
        persistentVolumeClaim:
          claimName: app-data-pvc

Dynamic Provisioning Benefits

  • No pre-provisioning: PV created automatically
  • Exact sizing: 100GB allocated as requested
  • Encryption: Data encrypted at rest
  • Performance: GP3 with specified IOPS
  • Expansion: Volume can be expanded later

Deployment Steps

  1. Create the StorageClass (cluster admin)
  2. Create the PersistentVolumeClaim
  3. Kubernetes automatically provisions PV
  4. Create the Deployment using the PVC
  5. Verify pod has access to storage

Dynamic Provisioning Best Practices

StorageClass Design

  • Create multiple StorageClasses for different performance tiers
  • Set appropriate default StorageClass for the cluster
  • Use descriptive names (fast-ssd, slow-hdd, shared-nfs)
  • Enable volume expansion when supported by the provisioner
  • Configure encryption for sensitive data

PVC Management

  • Use Retain policy for critical production data
  • Set appropriate storage requests (not too large, not too small)
  • Use WaitForFirstConsumer for topology-aware provisioning
  • Monitor PVC usage and set up alerts for near-capacity
  • Implement backup strategies for important data

Volume Binding Modes

Immediate
  • PV provisioned immediately when PVC is created
  • Good for storage that's available cluster-wide
  • May provision in wrong topology zone
WaitForFirstConsumer
  • PV provisioned when pod using PVC is created
  • Ensures optimal topology placement
  • Recommended for most use cases