Persistent Storage in Kubernetes

Understanding Persistent Volumes

Persistent Volumes (PV) provide a way to store data that persists beyond the lifecycle of a Pod. They are cluster resources that exist independently of Pods.

Basic Concepts

1. Persistent Volume (PV)

apiVersion: v1
kind: PersistentVolume
metadata:
  name: pv-example
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  storageClassName: standard
  hostPath:
    path: /mnt/data

2. Persistent Volume Claim (PVC)

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: pvc-example
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 5Gi
  storageClassName: standard

Storage Classes

Basic StorageClass

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

Cloud Provider Examples

1. AWS EBS

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: ebs-sc
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp3
  iopsPerGB: "10"
  encrypted: "true"

2. Azure Disk

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

3. Google Persistent Disk

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: gcp-pd
provisioner: kubernetes.io/gce-pd
parameters:
  type: pd-standard
  replication-type: none

Access Modes

ReadWriteOnce (RWO)
ReadOnlyMany (ROX)
ReadWriteMany (RWX)

Example with multiple access modes:

apiVersion: v1
kind: PersistentVolume
metadata:
  name: multi-access-pv
spec:
  capacity:
    storage: 10Gi
  accessModes:
    - ReadWriteOnce
    - ReadOnlyMany
  nfs:
    server: nfs-server.example.com
    path: "/share"

Dynamic Provisioning

StorageClass with Dynamic Provisioning

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

PVC Using Dynamic Provisioning

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: dynamic-pvc
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: fast
  resources:
    requests:
      storage: 100Gi

Real-World Examples

1. Database Storage

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mysql-data
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi
  storageClassName: fast
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: mysql
spec:
  serviceName: mysql
  replicas: 1
  selector:
    matchLabels:
      app: mysql
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
      - name: mysql
        image: mysql:8.0
        volumeMounts:
        - name: data
          mountPath: /var/lib/mysql
      volumes:
      - name: data
        persistentVolumeClaim:
          claimName: mysql-data

2. Shared File Storage

apiVersion: v1
kind: PersistentVolume
metadata:
  name: nfs-pv
spec:
  capacity:
    storage: 100Gi
  accessModes:
    - ReadWriteMany
  nfs:
    server: nfs-server.example.com
    path: "/shared"
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: nfs-pvc
spec:
  accessModes:
    - ReadWriteMany
  resources:
    requests:
      storage: 100Gi
  volumeName: nfs-pv

Volume Expansion

Expanding PVC

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: expandable-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 100Gi  # Can be increased later
  storageClassName: expandable-sc

StorageClass with Expansion

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: expandable-sc
provisioner: kubernetes.io/aws-ebs
allowVolumeExpansion: true
parameters:
  type: gp3

Backup and Restore

Volume Snapshot

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshot
metadata:
  name: data-snapshot
spec:
  volumeSnapshotClassName: csi-hostpath-snapclass
  source:
    persistentVolumeClaimName: data-pvc

Restore from Snapshot

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: restore-pvc
spec:
  dataSource:
    name: data-snapshot
    kind: VolumeSnapshot
    apiGroup: snapshot.storage.k8s.io
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi

Best Practices

1. Capacity Planning

Right-size volumes
Monitor usage
Plan for growth
Consider costs

2. Performance

Choose appropriate storage class
Monitor I/O metrics
Consider workload requirements
Use local storage when needed

3. Data Protection

Regular backups
Use snapshots
Implement disaster recovery
Test restore procedures

4. Security

Encrypt data at rest
Use appropriate access modes
Implement RBAC
Follow security policies

Troubleshooting

Common issues and solutions:

PVC Pending
- Check storage class
- Verify capacity
- Review access modes
- Check provisioner status
Volume Mount Issues
- Check permissions
- Verify paths
- Review mount options
- Check node capacity

Advanced Configurations

Local Volumes

apiVersion: v1
kind: PersistentVolume
metadata:
  name: local-pv
spec:
  capacity:
    storage: 100Gi
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Delete
  storageClassName: local-storage
  local:
    path: /mnt/disks/vol1
  nodeAffinity:
    required:
      nodeSelectorTerms:
      - matchExpressions:
        - key: kubernetes.io/hostname
          operator: In
          values:
          - node-1

CSI Integration

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: csi-sc
provisioner: csi.example.com
parameters:
  csi.storage.k8s.io/provisioner-secret-name: csi-secret
  csi.storage.k8s.io/provisioner-secret-namespace: default

Monitoring

Prometheus Metrics

apiVersion: monitoring.coreos.com/v1
kind: ServiceMonitor
metadata:
  name: storage-monitor
spec:
  selector:
    matchLabels:
      app: storage-provider
  endpoints:
  - port: metrics

Previous: Kubernetes Services and Ingress
Next: Monitoring Kubernetes Clusters

Conclusion

Understanding Persistent Volumes is crucial for managing stateful applications in Kubernetes. Proper configuration and management of storage resources ensures data persistence and reliability in your applications.