Storage in Kubernetes

Containers are stateless by design — when a container restarts, its filesystem is reset. For databases and any application that needs to persist data, Kubernetes provides a layered storage model.

Volumes

A Volume in Kubernetes is a directory accessible to containers in a Pod. Unlike container filesystems, Volumes survive container restarts (within the same Pod). However, they are tied to the Pod's lifecycle — when the Pod is deleted, the Volume's data may be lost depending on its type.

Common Volume Types

• emptyDir: Temporary storage shared between containers in the same Pod. Data deleted when Pod ends.
• hostPath: Mounts a directory from the node's filesystem. Use with caution — ties the Pod to a specific node.
• configMap / secret: Injects ConfigMap or Secret data as files.
• nfs: Mounts an NFS share; supports ReadWriteMany.
• awsElasticBlockStore / gcePersistentDisk: Cloud block storage (legacy; use PV/PVC instead).

spec:
  containers:
    - name: app
      image: nginx
      volumeMounts:
        - name: cache-vol
          mountPath: /tmp/cache
  volumes:
    - name: cache-vol
      emptyDir: {}

PersistentVolumes (PV) and PersistentVolumeClaims (PVC)

The PV/PVC model decouples storage provisioning from storage consumption:

• A PersistentVolume (PV) is a piece of storage provisioned by an admin or dynamically by a StorageClass. It's a cluster resource, like a node.
• A PersistentVolumeClaim (PVC) is a request for storage by a user/application. It specifies size and access mode. Kubernetes binds the PVC to a matching PV.

# PersistentVolumeClaim
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: db-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  storageClassName: gp3

# Using the PVC in a Pod
spec:
  containers:
    - name: postgres
      image: postgres:16
      volumeMounts:
        - name: data
          mountPath: /var/lib/postgresql/data
  volumes:
    - name: data
      persistentVolumeClaim:
        claimName: db-pvc

Access Modes

StorageClasses and Dynamic Provisioning

A StorageClass describes the type of storage available and enables dynamic provisioning — a PV is automatically created when a PVC is submitted:

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

Cloud providers supply CSI (Container Storage Interface) drivers that implement StorageClasses:

• AWS EBS CSI driver — block storage (RWO)
• AWS EFS CSI driver — shared filesystem (RWX)
• GCE Persistent Disk CSI driver
• Azure Disk / Azure File CSI drivers

Volume Snapshots

Kubernetes supports VolumeSnapshots for point-in-time backups of PVCs. Requires CSI drivers with snapshot support.

Next: ConfigMaps and Secrets — how to inject configuration and sensitive data into Pods without embedding them in container images.