World K4: Notes, Lockers & Packages

Storage for StatefulSets

You will learn: how a StatefulSet gives every pod its own locker, and keeps it.

Checked with Kubernetes 1.37 on 31 Oct 2026

The problem

You are here: cluster kind-dev namespace default

~/shop $ kubectl get pods -l app=ledgerNAME       READY   STATUS    RESTARTS   AGEledger-0   1/1     Running   0          28sledger-1   1/1     Running   0          26s

Two ledger trays, ledger-0 and ledger-1. Each keeps its own order book. One shared locker would mix the books. How does each get its own?

Watch

Tap the line where the locker form starts.

0 of 1 found

A StatefulSet carries a locker form: . For each tray, it fills in one claim, named after that tray.

Try it

Open the ledger. Then list the claims it made.

You are here: cluster kind-dev namespace default

dev-control-planeOpenManager

No trays here.

dev-workerOpen

No trays here.

dev-worker2Open

No trays here.

Time: +0s (sped up)

Predict

You scale the ledger to 3 trays. What is the new tray’s claim called?

Check

You are here: cluster kind-dev namespace default

~/shop $ kubectl scale statefulset ledger --replicas=3statefulset.apps/ledger scaled~/shop $ kubectl rollout status statefulset/ledger --timeout=180sWaiting for 1 pods to be ready...partitioned roll out complete: 3 new pods have been updated...~/shop $ kubectl get pvcNAME            STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   VOLUMEATTRIBUTESCLASS   AGEdata-ledger-0   Bound    pvc-12275be8-489d-4e5b-9103-3244568e6d85   1Gi        RWO            standard       <unset>                 29sdata-ledger-1   Bound    pvc-b5053239-899f-40a2-a64f-ef861fce2de1   1Gi        RWO            standard       <unset>                 27sdata-ledger-2   Bound    pvc-3730202e-598b-41af-996a-21fec8857129   1Gi        RWO            standard       <unset>                 1s

data-ledger-2 appeared, Bound to a new PV. The trays come up in order: 0, then 1, then 2.

Predict

ledger-0 wrote page 1 in its book. Now you delete the whole StatefulSet. What happens to the claims?

Check

You are here: cluster kind-dev namespace default

~/shop $ kubectl delete statefulset ledgerstatefulset.apps "ledger" deleted from default namespace~/shop $ kubectl get pvcNAME            STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   VOLUMEATTRIBUTESCLASS   AGEdata-ledger-0   Bound    pvc-12275be8-489d-4e5b-9103-3244568e6d85   1Gi        RWO            standard       <unset>                 28sdata-ledger-1   Bound    pvc-b5053239-899f-40a2-a64f-ef861fce2de1   1Gi        RWO            standard       <unset>                 26s~/shop $ kubectl apply -f ledger.yamlstatefulset.apps/ledger created~/shop $ kubectl rollout status statefulset/ledger --timeout=180sWaiting for 2 pods to be ready...Waiting for 1 pods to be ready...partitioned roll out complete: 2 new pods have been updated...~/shop $ kubectl exec ledger-0 -- cat /data/book.txtpage 1

The claims waited. The new ledger-0 got its old locker back, and read page 1.

You did it!

You can now give every StatefulSet pod its own lasting locker.

Go deeper (optional)

Want claims cleaned up? Set persistentVolumeClaimRetentionPolicy. whenDeleted and whenScaled each take Retain (the default) or Delete. It is stable since Kubernetes 1.32. Deleting claims deletes data, so think twice.

Real rep (optional), on a practice kind cluster:

Real mission

In the practice terminal above, cat ledger.yaml. Save it on your machine.
Open the ledger.
kubectl apply -f ledger.yaml
See one claim per tray.
kubectl get pvc
Delete the StatefulSet. The claims stay.
kubectl delete statefulset ledger
Delete the claims too, data and all.
kubectl delete pvc data-ledger-0 data-ledger-1

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