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Postpone Deletion of a Persistent Volume Claim in case It Is Used by a Pod (#6415)

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* Postpone Deletion of a Persistent Volume Claim in case It Is Used by a Pod

A new feature PVC Protection was added into K8s 1.9 that's why this documentation change is needed.

* Added tag at the top of each new area.

* Fix typo

* Fix: switched on in (all kubelets) -> (all K8s components).

* Added link to admission controller

* Moved PVC Protection configuration into Before you begin section.

* Added steps how to verify PVC Protection feature.

* Fixes for admission controller plugin description and for PVC Protection description in PVC lifecycle.

* Testing official rendering of enumerations (1., 2., 3., etc.)

* Re-write to address comments from review.

* Fixed definition when a PVC is in active use by a pod.
This commit is contained in:
Pavel Pospisil
2017-12-07 21:44:53 +01:00
committed by Zach Corleissen
parent 25f581ec39
commit a6eb85887d
5 changed files with 173 additions and 0 deletions
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docs/concepts/storage/persistent-volumes.md
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@@ -70,6 +70,29 @@ Pods use claims as volumes. The cluster inspects the claim to find the bound vol
Once a user has a claim and that claim is bound, the bound PV belongs to the user for as long as they need it. Users schedule Pods and access their claimed PVs by including a persistentVolumeClaim in their Pod's volumes block. [See below for syntax details](#claims-as-volumes).
### Persistent Volume Claim Protection
{% assign for_k8s_version="v1.9" %}{% include feature-state-alpha.md %}
The purpose of the PVC protection is to ensure that PVCs in active use by a pod are not removed from the system as this may result in data loss.
Note: PVC is in active use by a pod when the the pod status is `Pending` and the pod is assigned to a node or the pod status is `Running`.
When the [PVC protection alpha feature](/docs/tasks/administer-cluster/pvc-protection/) is enabled, if a user deletes a PVC in active use by a pod, the PVC is not removed immediately. PVC removal is postponed until the PVC is no longer actively used by any pods.
You can see that a PVC is protected when the PVC's status is `Terminating` and the `Finalizers` list includes `kubernetes.io/pvc-protection`:
```shell
kubectl described pvc hostpath
Name: hostpath
Namespace: default
StorageClass: example-hostpath
Status: Terminating
Volume:
Labels: <none>
Annotations: volume.beta.kubernetes.io/storage-class=example-hostpath
volume.beta.kubernetes.io/storage-provisioner=example.com/hostpath
Finalizers: [kubernetes.io/pvc-protection]
...
```
### Reclaiming
When a user is done with their volume, they can delete the PVC objects from the API which allows reclamation of the resource. The reclaim policy for a `PersistentVolume` tells the cluster what to do with the volume after it has been released of its claim. Currently, volumes can either be Retained, Recycled or Deleted.