Storage (10%)¶

This domain covers Kubernetes storage concepts including volumes, persistent volumes, and storage classes.

Volumes¶

emptyDir¶

Temporary storage that exists for the Pod's lifetime.

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-emptydir
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: cache
      mountPath: /cache
  volumes:
  - name: cache
    emptyDir: {}

Memory-backed emptyDir¶

volumes:
- name: memory-cache
  emptyDir:
    medium: Memory
    sizeLimit: 100Mi

hostPath¶

Mount a file or directory from the host node.

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-hostpath
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: data
      mountPath: /data
  volumes:
  - name: data
    hostPath:
      path: /data
      type: DirectoryOrCreate

hostPath Types¶

Type	Description
`""`	No checks (default)
`DirectoryOrCreate`	Create directory if not exists
`Directory`	Directory must exist
`FileOrCreate`	Create file if not exists
`File`	File must exist
`Socket`	Unix socket must exist

Persistent Volumes (PV)¶

PersistentVolume¶

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

Access Modes¶

Mode	Abbreviation	Description
`ReadWriteOnce`	RWO	Single node read-write
`ReadOnlyMany`	ROX	Multiple nodes read-only
`ReadWriteMany`	RWX	Multiple nodes read-write
`ReadWriteOncePod`	RWOP	Single pod read-write

Reclaim Policies¶

Policy	Description
`Retain`	Manual reclamation
`Delete`	Delete volume when PVC is deleted
`Recycle`	Basic scrub (deprecated)

PersistentVolumeClaim (PVC)¶

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

Using PVC in Pod¶

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-pvc
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: data
      mountPath: /data
  volumes:
  - name: data
    persistentVolumeClaim:
      claimName: pvc-claim

Storage Classes¶

StorageClass¶

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast
provisioner: kubernetes.io/aws-ebs
parameters:
  type: gp3
  iopsPerGB: "10"
reclaimPolicy: Delete
allowVolumeExpansion: true
volumeBindingMode: WaitForFirstConsumer

Volume Binding Modes¶

Mode	Description
`Immediate`	Bind PV immediately when PVC is created
`WaitForFirstConsumer`	Delay binding until Pod is scheduled

Dynamic Provisioning¶

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: dynamic-pvc
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  storageClassName: fast  # Uses StorageClass for dynamic provisioning

ConfigMap as Volume¶

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-configmap
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: config
      mountPath: /etc/config
  volumes:
  - name: config
    configMap:
      name: my-config
      items:
      - key: config.json
        path: app-config.json

Secret as Volume¶

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-secret
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: secret
      mountPath: /etc/secrets
      readOnly: true
  volumes:
  - name: secret
    secret:
      secretName: my-secret
      defaultMode: 0400

Projected Volumes¶

Combine multiple volume sources into a single directory.

apiVersion: v1
kind: Pod
metadata:
  name: pod-with-projected
spec:
  containers:
  - name: app
    image: nginx
    volumeMounts:
    - name: all-in-one
      mountPath: /projected-volume
  volumes:
  - name: all-in-one
    projected:
      sources:
      - secret:
          name: my-secret
      - configMap:
          name: my-config
      - downwardAPI:
          items:
          - path: labels
            fieldRef:
              fieldPath: metadata.labels

Volume Expansion¶

# StorageClass must have allowVolumeExpansion: true
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: expandable-pvc
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi  # Increase from original size
  storageClassName: fast

Storage Commands¶

# List PersistentVolumes
kubectl get pv

# List PersistentVolumeClaims
kubectl get pvc

# List StorageClasses
kubectl get sc

# Describe PV
kubectl describe pv pv-volume

# Delete PVC
kubectl delete pvc pvc-claim

# Patch PVC to expand
kubectl patch pvc pvc-claim -p '{"spec":{"resources":{"requests":{"storage":"20Gi"}}}}'

Volume Snapshots¶

VolumeSnapshotClass¶

apiVersion: snapshot.storage.k8s.io/v1
kind: VolumeSnapshotClass
metadata:
  name: csi-snapclass
driver: ebs.csi.aws.com
deletionPolicy: Delete

VolumeSnapshot¶

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

Restore from Snapshot¶

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

Key Concepts to Remember¶

PV - Cluster-level storage resource
PVC - Request for storage by a user
StorageClass - Dynamic provisioning template
Access Modes - RWO, ROX, RWX, RWOP
Reclaim Policies - Retain, Delete, Recycle

Practice Questions¶

What is the difference between PV and PVC?
How do you create a PVC that uses dynamic provisioning?
What access mode allows multiple nodes to read and write?
How do you expand a PVC?
What is the purpose of volumeBindingMode: WaitForFirstConsumer?

← Previous: Services & Networking | Back to CKA Overview | Next: Troubleshooting →