Persistent Storage

Containers and pods are ephemeral. When a pod is deleted, any data written to its container filesystem is lost. For stateful applications — databases, file stores, message queues — you need persistent storage that survives pod restarts and rescheduling.

Volumes

A Volume is a directory accessible to containers in a pod. Unlike a container's filesystem, a volume's lifetime is tied to the pod, not the container. Common volume types:

• emptyDir — created when the pod starts, deleted when it stops. Useful for sharing data between containers in the same pod.
• hostPath — mounts a file or directory from the host node. Useful for DaemonSets but risky in general because it ties the pod to a specific node.
• configMap / secret — mounts ConfigMap or Secret data as files.
• persistentVolumeClaim — the standard way to claim durable, network-attached storage.

PersistentVolumes and PersistentVolumeClaims

Kubernetes separates the provisioning of storage from its consumption:

• A PersistentVolume (PV) represents a piece of storage in the cluster (an AWS EBS volume, a GCP Persistent Disk, an NFS share, etc.). It is a cluster-wide resource.
• A PersistentVolumeClaim (PVC) is a request for storage by a pod. It specifies the size and access mode required.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: data-pvc
spec:
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
  storageClassName: standard

spec:
  containers:
    - name: db
      image: postgres:15
      volumeMounts:
        - mountPath: /var/lib/postgresql/data
          name: data
  volumes:
    - name: data
      persistentVolumeClaim:
        claimName: data-pvc

Access Modes

• ReadWriteOnce (RWO) — the volume can be mounted read-write by a single node
• ReadOnlyMany (ROX) — mounted read-only by many nodes simultaneously
• ReadWriteMany (RWX) — mounted read-write by many nodes simultaneously (requires a network filesystem like NFS or a cloud file storage service)

StorageClasses and Dynamic Provisioning

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast-ssd
provisioner: ebs.csi.aws.com
parameters:
  type: gp3
reclaimPolicy: Retain

A StorageClass defines a type of storage. When a PVC references a StorageClass, a dynamic provisioner creates the PV automatically — no manual pre-provisioning required. Cloud-managed Kubernetes clusters ship with default StorageClasses for their native block storage.

Working with Storage

# List PersistentVolumes
kubectl get pv

# List PersistentVolumeClaims
kubectl get pvc

# Describe a PVC to see binding status
kubectl describe pvc data-pvc

StatefulSets and VolumeClaimTemplates