Storage Overview¶

Container filesystems are ephemeral. For durable data, Kubernetes provides persistent storage primitives.

Ephemeral vs Persistent Storage¶

Ephemeral options:

emptyDir: temporary storage tied to pod lifetime.
hostPath: host-node path mount (use sparingly, mainly for node-level agents).

Persistent options:

PersistentVolume (PV)
PersistentVolumeClaim (PVC)
StorageClass

PV, PVC, and StorageClass¶

Object	Purpose	Typical owner
PV	Actual storage resource	Platform automation or admin
PVC	Workload storage request	App team
StorageClass	Provisioning policy	Platform team

PVC Example¶

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: db-data
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 20Gi
  storageClassName: standard

Access Modes¶

ReadWriteOnce (RWO): mounted read-write by one node at a time.
ReadWriteOncePod (RWOP): mounted read-write by one pod.
ReadWriteMany (RWX): mounted read-write by many nodes, only with compatible backends.
ReadOnlyMany (ROX): mounted read-only by many nodes.

StorageClass Example (CSI)¶

Prefer CSI drivers and dynamic provisioning.

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

Note: provisioner is environment-specific. Use the CSI driver for your platform.

Reclaim Policy¶

Delete: deleting PVC removes backing storage.
Retain: backing volume remains for manual recovery.

For critical stateful workloads, Retain can reduce accidental data loss risk.

Mounting a PVC in a Pod¶

apiVersion: v1
kind: Pod
metadata:
  name: app
spec:
  volumes:
    - name: app-storage
      persistentVolumeClaim:
        claimName: db-data
  containers:
    - name: app
      image: nginx:1.27
      volumeMounts:
        - name: app-storage
          mountPath: /data

Operational Checks¶

kubectl get pvc
kubectl get pv
kubectl describe pvc db-data

If PVC remains Pending, validate storage class name, CSI driver health, and topology constraints.