Bind PVs and PVCs Predictably

Why this matters

Stateful workloads need storage that outlives pods, nodes and sometimes namespaces. The two-object split (admin-owned PV, user-owned PVC) lets storage admins provision once while developers claim without knowing backends. The exam lives in the matching rules, because every Pending claim is a quiz with the answer in its events.

Concepts

A PV carries capacity, access modes (ReadWriteOnce, ReadOnlyMany, ReadWriteMany), a storage class name, a reclaim policy, and the backend details. A PVC requests capacity (minimum satisfied, not exact), access modes (intersection with the PV must cover the request), optionally a storage class, and optionally a selector for labels. Binding is exclusive: one Bound claim per volume until released.

The lifecycle runs Available to Bound on match, Bound to Released when the claim is deleted, then per the reclaim policy: Retain keeps the data (requiring manual cleanup before reuse), Delete removes volume plus data, Recycle is deprecated history. Released volumes never auto-rebind: stale data plus old claims must be cleared deliberately.

Worked example

One volume, one claim, one pod, receipts at each bind:

# admin carves the chunk (hostPath for the lab only)
apiVersion: v1
kind: PersistentVolume
metadata: { name: pv-demo }
spec:
  capacity: { storage: 2Gi }
  accessModes: [ReadWriteOnce]
  persistentVolumeReclaimPolicy: Retain
  hostPath: { path: /srv/pv-demo }
---
apiVersion: v1
kind: PersistentVolumeClaim
metadata: { name: claim-demo, namespace: demo }
spec:
  accessModes: [ReadWriteOnce]
  resources: { requests: { storage: 1Gi } }

kubectl get pv moves Available to Bound; the 1Gi claim fits the 2Gi volume because requests are minimums. Delete the claim and watch Released plus Retain: the data sits protected until an admin decides, which is exactly the safety net production wants.

Exam notes

Access-mode mismatch is the top Pending cause: a ReadWriteMany claim against ReadWriteOnce volumes waits forever. Storage class mismatch (named versus empty string) blocks binding silently across provisioners. And deleting a Bound PVC does not delete a Retain volume: the data survives, which is the feature, and the cleanup is yours.