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Co-authored-by: 杨朱 · Kiki <[email protected]>
Co-authored-by: Nate W <[email protected]>
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@deepakkinni @carlory @nate-double-u
3 people committed Jul 26, 2024
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45 changes: 23 additions & 22 deletions content/en/blog/_posts/2024-06-19-Honor-PV-Reclaim-Policy-Beta.md
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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).
associated with [Reclaim Policy](/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
releases the storage resource allocated for the PV. In essence, the reclaim
policy needs to honored on PV deletion.

With the recent Kubernetes v1.31 release, a beta feature lets you configure your
Expand All @@ -22,23 +22,23 @@ cluster to behave that way and honor the configured reclaim policy.
## How did reclaim work in previous Kubernetes releases?

[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
a user's request for storage. A PV and PVC are considered [Bound](/docs/concepts/storage/persistent-volumes/#Binding)
if a newly created PV or a matching PV is found. The PVs themselves are
backed by a volume allocated by the storage backend.

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.
PVC for a bound PV-PVC pair. However, there are no restrictions on deleting a PV
before deleting a PVC.

First, I'll demonstrate the behavior for clusters that are running an older version of Kubernetes.
First, I'll demonstrate the behavior for clusters running an older version of Kubernetes.

#### Retrieve an PVC that is bound to a PV
#### Retrieve a PVC that is bound to a PV

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:
The following output shows the PVC and its `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
Expand All @@ -63,7 +63,7 @@ persistentvolume "pvc-6791fdd4-5fad-438e-a7fb-16410363e3da" deleted
kubectl get pv pvc-6791fdd4-5fad-438e-a7fb-16410363e3da
```

It can be observed that the PV is in `Terminating` state
It can be observed that the PV is in a `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
Expand Down Expand Up @@ -91,14 +91,14 @@ kubectl get pv pvc-6791fdd4-5fad-438e-a7fb-16410363e3da
Error from server (NotFound): persistentvolumes "pvc-6791fdd4-5fad-438e-a7fb-16410363e3da" not found
```

Although the PV is deleted the underlying storage resource is not deleted, and
Although the PV is deleted, the underlying storage resource is not deleted and
needs to be removed manually.

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
To sum up, the reclaim policy associated with the Persistent Volume is currently
ignored under certain circumstances. 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,
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.

## PV reclaim policy with Kubernetes v1.31
Expand All @@ -107,12 +107,13 @@ The new behavior ensures that the underlying storage object is deleted from the

#### How to enable new behavior?

To make use of the new behavior, you must have upgraded your cluster to the v1.31 release of Kubernetes.
You need to make sure that you are running the CSI [`external-provisioner`](https://github.com/kubernetes-csi/external-provisioner) version `5.0.1`, or later.
To take advantage of the new behavior, you must have upgraded your cluster to the v1.31 release of Kubernetes
and run the CSI [`external-provisioner`](https://github.com/kubernetes-csi/external-provisioner) version `5.0.1` or later.

#### How does it work?

For CSI volumes, 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.
For CSI volumes, 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 the backend is deleted.
`

An example of a PV with the finalizer, notice the new finalizer in the finalizers list

Expand Down Expand Up @@ -159,7 +160,7 @@ status:
phase: Bound
```
The presence of the finalizer prevents the PV object from being removed from the
The 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/).
Expand All @@ -168,11 +169,11 @@ Similarly, the finalizer `kubernetes.io/pv-controller` is added to dynamically p

#### What about CSI migrated volumes?

The fix is applicable to CSI migrated volumes as well.
The fix applies to CSI migrated volumes as well.

### Some caveats

The fix is not applicable to statically provisioned in-tree plugin volumes.
The fix does not apply to statically provisioned in-tree plugin volumes.

### References

Expand All @@ -190,4 +191,4 @@ Special thanks to the following people for the insightful reviews, thorough cons
* Xing Yang (xing-yang)
* Matthew Wong (wongma7)

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.
Join the [Kubernetes Storage Special Interest Group (SIG)](https://github.com/kubernetes/community/tree/master/sig-storage) if you're interested in getting involved with the design and development of CSI or any part of the Kubernetes Storage system. We’re rapidly growing and always welcome new contributors.

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