Kubernetes Storage & Persistence - Complete Data Management Guide

The Container Data Problem

Containers are Ephemeral and Stateless

You usually don't store data in containers
Non-persistent data is stored locally on a writable layer
This is the default behavior - just write to the filesystem
When containers are destroyed, so is the data inside them

Definition of 'Ephemeral'

ephemerous (ɪˈfɛmərəs)

ADJECTIVE

1. zoology: relating to an ephemeron

2. short-lived

Important: Without persistent storage, any data written to a container's filesystem will be lost when the container is terminated, updated, or rescheduled to a different node.

The Solution: Volumes

We need to store data outside the container in a Volume. Volumes let containers store data into external storage systems.

Container

Volume

→

External Storage

Data Persistence

Data survives container restarts, updates, and rescheduling

Data Sharing

Multiple containers can share the same volume

Storage Plugins

Vendors create plugins according to Container Storage Interface

Storage Provisioning Methods

Static Provisioning

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

Admin manually creates PersistentVolumes
Developer claims them with PersistentVolumeClaims
Good for small clusters or specific storage requirements
More administrative overhead

Dynamic Provisioning

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

Storage automatically provisioned on demand
Uses StorageClasses to define provisioners
Ideal for cloud environments and large clusters
Less administrative overhead

StorageClass Example

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

This StorageClass uses AWS EBS with gp2 volumes and ext4 filesystem

Common Volume Types

HostPath

Mounts a directory from the host node's filesystem

                            hostPath:

                              path: /data

Cloud Volumes

AWS EBS, GCE PD, Azure Disk

                            awsElasticBlockStore:

                              volumeID: vol-123456

NFS

Network File System for shared storage

                            nfs:

                              server: nfs-server.local

                              path: /exports/data

ConfigMap/Secret

Mount configuration data as files

                            configMap:

                              name: app-config

EmptyDir

Temporary directory that shares a pod's lifetime

emptyDir: {}

CSI Volumes

Container Storage Interface for vendor plugins

                            csi:

                              driver: ebs.csi.aws.com

Essential Storage Commands

List Storage Resources

                        kubectl get pv

                        kubectl get pvc

                        kubectl get storageclass

Get PersistentVolumes, PersistentVolumeClaims, and StorageClasses

Describe Resources

                        kubectl describe pv [pv-name]

                        kubectl describe pvc [pvc-name]

                        kubectl describe storageclass [sc-name]

Get detailed information about storage resources

Create from YAML

                        kubectl apply -f pv.yaml

                        kubectl apply -f pvc.yaml

                        kubectl apply -f storageclass.yaml

Create storage resources from configuration files

Delete Resources

                        kubectl delete pv [pv-name]

                        kubectl delete pvc [pvc-name]

                        kubectl delete -f storage-config.yaml

Delete storage resources

Complete Example: Database with Persistent Storage

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

---

# Deployment with Volume
apiVersion: apps/v1
kind: Deployment
metadata:
  name: mysql
spec:
  selector:
    matchLabels:
      app: mysql
  strategy:
    type: Recreate
  template:
    metadata:
      labels:
        app: mysql
    spec:
      containers:
      - image: mysql:8.0
        name: mysql
        env:
        - name: MYSQL_ROOT_PASSWORD
          valueFrom:
            secretKeyRef:
              name: mysql-secret
              key: password
        ports:
        - containerPort: 3306
          name: mysql
        volumeMounts:
        - name: mysql-persistent-storage
          mountPath: /var/lib/mysql
      volumes:
      - name: mysql-persistent-storage
        persistentVolumeClaim:
          claimName: mysql-pvc

Key Points

PVC requests 10GB of storage from the "fast" StorageClass
Deployment mounts the PVC at /var/lib/mysql in the container
MySQL data persists even if the pod is rescheduled
Using Recreate strategy ensures only one pod accesses the volume

Access Modes

ReadWriteOnce (RWO): Read-write by a single node
ReadOnlyMany (ROX): Read-only by many nodes
ReadWriteMany (RWX): Read-write by many nodes
ReadWriteOncePod (RWOP): Read-write by a single pod

Storage Best Practices

Planning & Configuration

Use dynamic provisioning for most use cases
Choose appropriate access modes for your workload
Set proper storage class based on performance needs
Use StatefulSets for stateful applications
Consider volume snapshots for backup strategies

Operations & Maintenance

Monitor storage usage and set up alerts
Understand reclaim policies (Delete, Retain, Recycle)
Use volume expansion features when available
Test backup and restore procedures regularly
Document storage requirements for each application

StatefulSet Example

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: web
spec:
  serviceName: "nginx"
  replicas: 3
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      containers:
      - name: nginx
        image: nginx:latest
        volumeMounts:
        - name: www
          mountPath: /usr/share/nginx/html
  volumeClaimTemplates:
  - metadata:
      name: www
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: "fast"
      resources:
        requests:
          storage: 1Gi

StatefulSets automatically create PVCs for each pod (web-0, web-1, web-2)