Give pods persistent storage — CKA الفصل 11

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المهارات في هذا الفصل

StorageClasses والتوفير الديناميكي و PV و PVC

Know the storage objects

The app asks with a PVC; Kubernetes binds it to a matching PV (existing or newly created).

Object	Who makes it	Meaning
StorageClass	Admin	A type of storage + its provisioner
PersistentVolume	Admin or provisioner	A piece of real storage
PersistentVolumeClaim	App team	"I need 10 Gi, ReadWriteOnce"
Volume in the pod	App team	Mounts the PVC into a container

11.2

Know access modes and reclaim policies

Access modes say how many nodes may mount the volume; the reclaim policy says what happens after the PVC is deleted.

Access mode	Short	Meaning
ReadWriteOnce	RWO	Read-write by one node
ReadOnlyMany	ROX	Read-only by many nodes
ReadWriteMany	RWX	Read-write by many nodes (NFS, CephFS, Azure Files)
ReadWriteOncePod	RWOP	Read-write by one pod only

Reclaim policy	After the PVC is deleted
Delete	The PV and the real disk are deleted (default for dynamic)
Retain	The PV stays (status Released); an admin cleans up by hand

11.3

Use dynamic provisioning

With a StorageClass, a PVC alone is enough — the provisioner creates the PV.

storageclass.yaml

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: fast
  annotations: { storageclass.kubernetes.io/is-default-class: "true" }
provisioner: rancher.io/local-path
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer
allowVolumeExpansion: true
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata: { name: db-data, namespace: shop }
spec:
  accessModes: [ReadWriteOnce]
  storageClassName: fast
  resources:
    requests: { storage: 10Gi }

$kubectl get storageclass
$kubectl get pvc,pv -n shop
$kubectl patch pvc db-data -n shop -p '{"spec":{"resources":{"requests":{"storage":"20Gi"}}}}'

تذكّر

WaitForFirstConsumer creates the volume only when a pod uses it — in the zone of that pod's node. The PVC stays Pending until then; that is normal.

11.4

Create a PV by hand

Without a provisioner, an admin creates PVs; a PVC with the same class, size and mode binds to one.

pv.yaml

apiVersion: v1
kind: PersistentVolume
metadata: { name: pv-logs }
spec:
  capacity: { storage: 5Gi }
  accessModes: [ReadWriteOnce]
  persistentVolumeReclaimPolicy: Retain
  storageClassName: manual
  hostPath: { path: /mnt/data/logs }

11.5

Mount the PVC in a pod

The pod refers to the claim, the container mounts the volume.

pod-pvc.yaml

apiVersion: v1
kind: Pod
metadata: { name: db, namespace: shop }
spec:
  containers:
    - name: postgres
      image: postgres:16
      env: [{ name: POSTGRES_PASSWORD, value: change-me }]
      volumeMounts:
        - { name: data, mountPath: /var/lib/postgresql/data }
  volumes:
    - name: data
      persistentVolumeClaim: { claimName: db-data }

$kubectl exec db -n shop -- df -h /var/lib/postgresql/data
$kubectl describe pvc db-data -n shop

11.6

Use other volume types

Not every volume is persistent.

Volume	Lives as long as	Use
`emptyDir`	The pod	Scratch space, shared between containers of a pod
`hostPath`	The node	Node agents; avoid for apps (pins the pod to a node)
`configMap`, `secret`	The object	Config files
`persistentVolumeClaim`	The PVC	App data

كل الأوامر في هذا الفصل

kubectl