9.5 Storage and Persistence

Managing Data in Kubernetes

Kubernetes provides several storage options for persistent data, from simple volumes to enterprise storage solutions.

Volumes

Basic Storage Types

# Pod with different volume types
apiVersion: v1
kind: Pod
metadata:
  name: storage-demo
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: empty-vol
      mountPath: /tmp/empty
    - name: host-vol
      mountPath: /tmp/host
    - name: config-vol
      mountPath: /etc/config
  volumes:
  - name: empty-vol
    emptyDir: {}              # Temporary storage
  - name: host-vol
    hostPath:                 # Node filesystem
      path: /data
  - name: config-vol
    configMap:                # Configuration data
      name: app-config

Persistent Volumes

Long-term Storage

Persistent Volumes (PV) provide durable storage that exists beyond pod lifecycle.

Persistent Volume

# Manual PV creation
apiVersion: v1
kind: PersistentVolume
metadata:
  name: postgres-pv
spec:
  capacity:
    storage: 10Gi
  accessModes:
  - ReadWriteOnce
  persistentVolumeReclaimPolicy: Retain
  hostPath:
    path: /data/postgres

Persistent Volume Claim

# Request storage
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: postgres-pvc
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi

Using PVC in Pod

# Pod using PVC
apiVersion: v1
kind: Pod
metadata:
  name: postgres
spec:
  containers:
  - name: postgres
    image: postgres:15
    volumeMounts:
    - name: postgres-storage
      mountPath: /var/lib/postgresql/data
  volumes:
  - name: postgres-storage
    persistentVolumeClaim:
      claimName: postgres-pvc

Storage Classes

Dynamic Provisioning

Storage Classes enable automatic PV creation when PVCs are requested.

# AWS EBS Storage Class
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast-ssd
provisioner: ebs.csi.aws.com
parameters:
  type: gp3
  fsType: ext4
reclaimPolicy: Delete
allowVolumeExpansion: true

Using Storage Class

# PVC with Storage Class
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: app-storage
spec:
  accessModes:
  - ReadWriteOnce
  storageClassName: fast-ssd
  resources:
    requests:
      storage: 20Gi

StatefulSet Storage

Volume Claim Templates

StatefulSets can automatically create PVCs for each pod.

# StatefulSet with storage
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: database
spec:
  serviceName: database
  replicas: 3
  selector:
    matchLabels:
      app: database
  template:
    metadata:
      labels:
        app: database
    spec:
      containers:
      - name: postgres
        image: postgres:15
        volumeMounts:
        - name: data
          mountPath: /var/lib/postgresql/data
  volumeClaimTemplates:
  - metadata:
      name: data
    spec:
      accessModes: ["ReadWriteOnce"]
      storageClassName: fast-ssd
      resources:
        requests:
          storage: 50Gi

ConfigMaps and Secrets as Volumes

Configuration Files

# ConfigMap as volume
apiVersion: v1
kind: ConfigMap
metadata:
  name: nginx-config
data:
  nginx.conf: |
    server {
      listen 80;
      location / {
        proxy_pass http://backend;
      }
    }

# Using ConfigMap in pod
apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
    image: nginx
    volumeMounts:
    - name: config
      mountPath: /etc/nginx/conf.d
  volumes:
  - name: config
    configMap:
      name: nginx-config

Backup and Snapshots

Volume Snapshots

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

Restore from Snapshot

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

Essential Commands

# Persistent Volumes
kubectl get pv
kubectl get pvc
kubectl describe pv postgres-pv
kubectl describe pvc postgres-pvc

# Storage Classes
kubectl get storageclass
kubectl describe storageclass fast-ssd

# Volume usage
kubectl exec postgres-0 -- df -h /var/lib/postgresql/data

# Snapshots
kubectl get volumesnapshots
kubectl get volumesnapshotclasses

What’s Next?

Next, we’ll explore Configuration Management with ConfigMaps and Secrets.