[SHORT] Extending Kubernetes StatefulSet PVC Without Downtime

Kubernetes troubleshooting series

Photo by Zac Durant on Unsplash

Problem

In Kubernetes, the size of a Persistent Volume Claim (PVC) cannot be directly updated for a StatefulSet object. This limitation exists because the PVC is bound to a Persistent Volume (PV) that has a fixed capacity.

When you create a PVC for a StatefulSet, it requests a specific amount of storage capacity. This request is fulfilled by binding the PVC to an available PV that meets the capacity requirement. Once the PVC is bound to a PV, the capacity cannot be changed because it would require modifying the underlying storage resource.

Solution

To extend the size of a PVC in a StatefulSet, you generally need to follow these steps:

1. Update the PVC object

Make sure that your StorageClass has ALLOWVOLUMEEXPANSION=true property

$ kubectl edit pvc <YOUR_PVC_NAME> # Change "storage" from both places

$ kubectl describe pvc <YOUR_STATEFULSET_NAME> # Now when you describe your PVC you should see the changes

2. Delete the StatefulSet object

$ kubectl delete sts --cascade=orphan <YOUR_STATEFULSET_NAME> # Use the flag --cascade=orphan to delete the StatefulSet and keep its pods running

3. Update the StatefulSet manifest and redeploy it

$ kubectl apply -f sts.yaml # Before applying you need to change the "storage" size as well in sts.yaml file
$ kubectl rollout restart sts <YOUR_STATEFULSET_NAME> # Restart the pods one at a time, the pod's PVC will be extended during the restart

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