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Doc: Add blogpost for honor PV reclaim policy fix
Signed-off-by: Deepak Kinni <dkinni@vmware.com>
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.../_posts/2021-11-18-prevent-persistentvolume-leaks-when-deleting-out-of-order.md
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| --- | ||
| layout: blog | ||
| title: "Kubernetes 1.23 Prevent PersistentVolume leaks when deleting out of order" | ||
| date: 2021-12-15T10:00:00-08:00 | ||
| slug: kubernetes-1-23-prevent-persistentvolume-leaks-when-deleting-out-of-order | ||
| --- | ||
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| **Author:** Deepak Kinni (VMware) | ||
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| [PersistentVolume](/docs/concepts/storage/persistent-volumes/) (or PVs for short) are | ||
| associated with [Reclaim Policy](https://kubernetes.io/docs/concepts/storage/persistent-volumes/#reclaim-policy). | ||
| The Reclaim Policy is used to determine the actions that need to be taken by the storage | ||
| backend on deletion of the PV. | ||
| Where the reclaim policy is `Delete`, the expectation is that the storage backend | ||
| releases the storage resource that was allocated for the PV. In essence, the reclaim | ||
| policy needs to honored on PV deletion. | ||
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| With the recent Kubernetes v1.23 release, an alpha feature lets you configure your | ||
| cluster to behave that way and honor the configured reclaim policy. | ||
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| ## How did reclaim work in previous Kubernetes releases? | ||
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| [PersistentVolumeClaim](/docs/concepts/storage/persistent-volumes/#Introduction) (or PVC for short) is | ||
| a request for storage by a user. A PV and PVC are considered [Bound](/docs/concepts/storage/persistent-volumes/#Binding) | ||
| if there is a newly created PV or a matching PV is found. The PVs themselves are | ||
| backed by a volume allocated by the storage backend. | ||
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| Normally, if the volume is to be deleted, then the expectation is to delete the | ||
| PVC for a bound PV-PVC pair. However, there are no restrictions to delete a PV | ||
| prior to deleting a PVC. | ||
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| First, I'll demonstrate the behavior for clusters that are running an older version of Kubernetes. | ||
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| #### Retrieve an PVC that is bound to a PV | ||
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| Retrieve an existing PVC `example-vanilla-block-pvc` | ||
| ``` | ||
| kubectl get pvc example-vanilla-block-pvc | ||
| ``` | ||
| The following output shows the PVC and it's `Bound` PV, the PV is shown under the `VOLUME` column: | ||
| ``` | ||
| NAME STATUS VOLUME CAPACITY ACCESS MODES STORAGECLASS AGE | ||
| example-vanilla-block-pvc Bound pvc-6791fdd4-5fad-438e-a7fb-16410363e3da 5Gi RWO example-vanilla-block-sc 19s | ||
| ``` | ||
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| #### Delete PV | ||
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| When I try to delete a bound PV, the cluster blocks and the `kubectl` tool does | ||
| not return back control to the shell; for example: | ||
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| ``` | ||
| kubectl delete pv pvc-6791fdd4-5fad-438e-a7fb-16410363e3da | ||
| ``` | ||
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| ``` | ||
| persistentvolume "pvc-6791fdd4-5fad-438e-a7fb-16410363e3da" deleted | ||
| ^C | ||
| ``` | ||
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| Retrieving the PV: | ||
| ``` | ||
| kubectl get pv pvc-6791fdd4-5fad-438e-a7fb-16410363e3da | ||
| ``` | ||
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| It can be observed that the PV is in `Terminating` state | ||
| ``` | ||
| NAME CAPACITY ACCESS MODES RECLAIM POLICY STATUS CLAIM STORAGECLASS REASON AGE | ||
| pvc-6791fdd4-5fad-438e-a7fb-16410363e3da 5Gi RWO Delete Terminating default/example-vanilla-block-pvc example-vanilla-block-sc 2m23s | ||
| ``` | ||
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| #### Delete PVC | ||
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| ``` | ||
| kubectl delete pvc example-vanilla-block-pvc | ||
| ``` | ||
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| The following output is seen if the PVC gets successfully deleted: | ||
| ``` | ||
| persistentvolumeclaim "example-vanilla-block-pvc" deleted | ||
| ``` | ||
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| The PV object from the cluster also gets deleted. When attempting to retrieve the PV | ||
| it will be observed that the PV is no longer found: | ||
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| ``` | ||
| kubectl get pv pvc-6791fdd4-5fad-438e-a7fb-16410363e3da | ||
| ``` | ||
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| ``` | ||
| Error from server (NotFound): persistentvolumes "pvc-6791fdd4-5fad-438e-a7fb-16410363e3da" not found | ||
| ``` | ||
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| Although the PV is deleted the underlying storage resource is not deleted, and | ||
| needs to be removed manually. | ||
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| To sum it up, the reclaim policy associated with the Persistent Volume is currently | ||
| ignored under certain circumstance. For a `Bound` PV-PVC pair the ordering of PV-PVC | ||
| deletion determines whether the PV reclaim policy is honored. The reclaim policy | ||
| is honored if the PVC is deleted first, however, if the PV is deleted prior to | ||
| deleting the PVC then the reclaim policy is not exercised. As a result of this behavior, | ||
| the associated storage asset in the external infrastructure is not removed. | ||
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| ## PV reclaim policy with Kubernetes v1.23 | ||
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| The new behavior ensures that the underlying storage object is deleted from the backend when users attempt to delete a PV manually. | ||
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| #### How to enable new behavior? | ||
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| To make use of the new behavior, you must have upgraded your cluster to the v1.23 release of Kubernetes. | ||
| You need to make sure that you are running the CSI [`external-provisioner`](https://github.com/kubernetes-csi/external-provisioner) version `4.0.0`, or later. | ||
| You must also enable the `HonorPVReclaimPolicy` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) for the | ||
| `external-provisioner` and for the `kube-controller-manager`. | ||
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| If you're not using a CSI driver to integrate with your storage backend, the fix isn't | ||
| available. The Kubernetes project doesn't have a current plan to fix the bug for in-tree | ||
| storage drivers: the future of those in-tree drivers is deprecation and migration to CSI. | ||
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| #### How does it work? | ||
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| The new behavior is achieved by adding a finalizer `external-provisioner.volume.kubernetes.io/finalizer` on new and existing PVs, the finalizer is only removed after the storage from backend is deleted. | ||
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| An example of a PV with the finalizer, notice the new finalizer in the finalizers list | ||
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| ``` | ||
| kubectl get pv pvc-a7b7e3ba-f837-45ba-b243-dec7d8aaed53 -o yaml | ||
| ``` | ||
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| ```yaml | ||
| apiVersion: v1 | ||
| kind: PersistentVolume | ||
| metadata: | ||
| annotations: | ||
| pv.kubernetes.io/provisioned-by: csi.vsphere.vmware.com | ||
| creationTimestamp: "2021-11-17T19:28:56Z" | ||
| finalizers: | ||
| - kubernetes.io/pv-protection | ||
| - external-provisioner.volume.kubernetes.io/finalizer | ||
| name: pvc-a7b7e3ba-f837-45ba-b243-dec7d8aaed53 | ||
| resourceVersion: "194711" | ||
| uid: 087f14f2-4157-4e95-8a70-8294b039d30e | ||
| spec: | ||
| accessModes: | ||
| - ReadWriteOnce | ||
| capacity: | ||
| storage: 1Gi | ||
| claimRef: | ||
| apiVersion: v1 | ||
| kind: PersistentVolumeClaim | ||
| name: example-vanilla-block-pvc | ||
| namespace: default | ||
| resourceVersion: "194677" | ||
| uid: a7b7e3ba-f837-45ba-b243-dec7d8aaed53 | ||
| csi: | ||
| driver: csi.vsphere.vmware.com | ||
| fsType: ext4 | ||
| volumeAttributes: | ||
| storage.kubernetes.io/csiProvisionerIdentity: 1637110610497-8081-csi.vsphere.vmware.com | ||
| type: vSphere CNS Block Volume | ||
| volumeHandle: 2dacf297-803f-4ccc-afc7-3d3c3f02051e | ||
| persistentVolumeReclaimPolicy: Delete | ||
| storageClassName: example-vanilla-block-sc | ||
| volumeMode: Filesystem | ||
| status: | ||
| phase: Bound | ||
| ``` | ||
| The presence of the finalizer prevents the PV object from being removed from the | ||
| cluster. As stated previously, the finalizer is only removed from the PV object | ||
| after it is successfully deleted from the storage backend. To learn more about | ||
| finalizers, please refer to [Using Finalizers to Control Deletion](/blog/2021/05/14/using-finalizers-to-control-deletion/). | ||
| #### What about CSI migrated volumes? | ||
| The fix is applicable to CSI migrated volumes as well. However, when the feature | ||
| `HonorPVReclaimPolicy` is enabled on 1.23, and CSI Migration is disabled, the finalizer | ||
| is removed from the PV object if it exists. | ||
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| ### Some caveats | ||
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| 1. The fix is applicable only to CSI volumes and migrated volumes. In-tree volumes will exhibit older behavior. | ||
| 2. The fix is introduced as an alpha feature in the [external-provisioner](https://github.com/kubernetes-csi/external-provisioner) under the feature gate `HonorPVReclaimPolicy`. The feature is disabled by default, and needs to be enabled explicitly. | ||
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| ### References | ||
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| * [KEP-2644](https://github.com/kubernetes/enhancements/tree/master/keps/sig-storage/2644-honor-pv-reclaim-policy) | ||
| * [Volume leak issue](https://github.com/kubernetes-csi/external-provisioner/issues/546) | ||
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| ### How do I get involved? | ||
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| The Kubernetes Slack channel [SIG Storage communication channels](https://github.com/kubernetes/community/blob/master/sig-storage/README.md#contact) are great mediums to reach out to the SIG Storage and migration working group teams. | ||
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| Special thanks to the following people for the insightful reviews, thorough consideration and valuable contribution: | ||
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| * Jan Šafránek (jsafrane) | ||
| * Xing Yang (xing-yang) | ||
| * Matthew Wong (wongma7) | ||
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| Those interested in getting involved with the design and development of CSI or any part of the Kubernetes Storage system, join the [Kubernetes Storage Special Interest Group (SIG)](https://github.com/kubernetes/community/tree/master/sig-storage). We’re rapidly growing and always welcome new contributors. |