Persistent Volumes | Selectel Documentation

Permanent volumes

For your information

Cloud platform network disk-based persistent volume (PV) connectivity is not available in Managed Kubernetes clusters on dedicated servers.

A Persistent Volume is used for long-term data storage in a Managed Kubernetes cluster. Kubernetes uses PersistentVolume (PV), PersistentVolumeClaim (PVC), and StorageClass objects to manage persistent volumes.

For persistent volumes in Managed Kubernetes, we recommend using network disks from the Selectel cloud platform. You can create a persistent volume on a local disk, but the data will be deleted when the node is deleted.

After you create a persistent volume, you can enlarge and delete it.

You can view all persistent volumes in the Control Panel: from the top menu, click Products and select Cloud Servers → Disk section.

Create a permanent volume⁠

For your information

Topology-Aware Volume Provisioning is not available.

Create a StorageClass or use an existing StorageClass.
Create a PersistentVolumeClaim.
Create a sub with a persistent volume.

1. Create StorageClass⁠

The StorageClass object is used to create a PersistentVolume. StorageClass allows you to pre-describe the configuration of persistent volumes that will be needed in the cluster operation.

When a cluster is created, a single StorageClass will be automatically created with a fast network disk in the pool where the cluster node group is located.

Create a yaml file with a manifest for the StorageClass object.

Example of a StorageClass manifest for a fast disk in the ru-1a pool:
```
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: fast.ru-1a
provisioner: cinder.csi.openstack.org
parameters:
  type: fast.ru-1a
  availability: ru-1a
  fsType: ext4
allowVolumeExpansion: true
```
Here fast.ru-1a is of type StorageClass.

You can use other ready-made StorageClass manifests.
Apply the manifest:
```
kubectl apply -f <storage-class.yaml>
```
Specify <storage-class.yaml> is the name of the manifest yaml file to create a new StorageClass.

Verify that a StorageClass object has been created:

kubectl get sc

The response will list the created StorageClass objects:

NAME         PROVISIONER                RECLAIMPOLICY   VOLUMEBINDINGMODE   ALLOWVOLUMEEXPANSION   AGE
fast.ru-1a   cinder.csi.openstack.org   Delete          Immediate           true                   16m

StorageClass type⁠

StorageClass-type format- <disk type>.<the pool segment in which it resides>.

The disk types correspond to the Selectel Cloud Platform network disks:

Network disk type	Name in StorageClass
Fast SSD	fast
Basic HDD	basic
Basic SSD	basicssd
Universal SSD	universal

For example, to create a fast disk in the ru-1a pool segment, you must add to the StorageClass description:

parameters:
  type: fast.ru-1a
  availability: ru-1a

2. Create a PersistentVolumeClaim⁠

For your information

Working with volumes is possible only in ReadWriteOnce mode — one volume can be mounted to only one node, and only one pod can be connected to a persistent volume. If several pods are connected to one PV, data may be corrupted. To work with ReadWriteMany mode (mounting a volume to multiple nodes), you can connect file storage to the cluster nodes.

Create a yaml file with a manifest for the PersistentVolumeClaim (PVC) object.

Manifesto example:
```
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pv-claim
spec:
  storageClassName: fast.ru-1a
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi
```
The pool in the PVC manifest must match the pool of the node to which the PVC is to be connected. If you use multiple pools for cluster nodes and PVCs, specify in the description of Pod objects their pool mapping.
Apply the manifest:
```
kubectl apply -f <pvc.yaml>
```
Specify <pvc.yaml> is the name of the manifest yaml file to create a new PersistentVolumeClaim.

3. Create a sub with a persistent volume⁠

If you create a Pod with a persistent volume, the volume is preserved when the Pod is deleted.

Create a yaml file with a manifest to create a new persistent volume feed.

Manifesto example:

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    app: webservice
spec:
  containers:
  - name: nginx
    image: library/nginx:1.17-alpine
    ports:
    - containerPort: 80
    volumeMounts:
      - mountPath: "/var/www/html"
        name: data
  volumes:
    - name: data
      persistentVolumeClaim:
        claimName: my-pv-claim

When creating a submission with the securityContext.fsGroup parameter, the persistent volume will not be mounted with the appropriate GID. To solve this problem, add fsType: ext4 in the StorageClass parameters.

Apply the manifest:
```
kubectl apply -f <pod-with-pv.yaml>
```
Specify <pod-with-pv.yaml> is the name of the manifest yaml file to create a new pod with a persistent volume.

Verify that PersistentVolume has been created:

kubectl get pv

A list of PersistentVolumes will appear in the response:

NAME CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS   CLAIM                 STORAGECLASS   REASON   AGE
pvc-f171f94c-0d38-41be-947e-2f5d7e46a6c3   10Gi       RWO            Delete           Bound    default/my-pv-claim   fast.ru-1a              97s

Increase the permanent volume⁠

1. Check the amount of occupied space in the PVC⁠

Recognize the amount of occupied space in the PVC:

kubectl -n <namespace> exec <pod_name> -- df -ah

Specify:

<namespace> — namespace where the PVC is located;
<pod_name> — the name of the pod that uses PVC.

2. Check quotas⁠

To determine that there are enough resources to grow the persistent volume, check the quotas and change them if necessary.

3. Allow permanent volume enlargement⁠

In the parameters of the StorageClass object, specify allowVolumeExpansion: true.

Manifesto example:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
 name: example-vol-default
provisioner: vendor-name.example/magicstorage
parameters:
 resturl: "http://192.168.10.100:8080"
 restuser: ""
 secretNamespace: ""
 secretName: ""
allowVolumeExpansion: true
reclaimPolicy: Delete

4. Delete pods with the volume to be enlarged⁠

Check to see which pods are using PVC:
```
kubectl describe pvc <pvc_name>
```
Specify <pvc_name> is the name of the PersistentVolumeClaim.
Remove pods that use PVC:
```
kubectl delete pod <pod_name>
```
Specify <pod_name> is the name of the pod.

5. Modify the PersistentVolumeClaim manifest⁠

Open the yaml file with the manifest for PersistentVolumeClaim and change the storage parameter:

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: my-pv-claim
spec:
  storageClassName: fast.ru-1a
  accessModes:
    - ReadWriteOnce
  resources:
    requests:
      storage: 10Gi

Create PersistentVolumeClaim — apply the manifest:
```
kubectl apply -f <pvc_name>
```
Specify <pvc_name> is the name of the PersistentVolumeClaim.

Run under using this PVC.

Manifesto example:

apiVersion: v1
kind: Pod
metadata:
  name: nginx
  labels:
    app: webservice
spec:
  containers:
  - name: nginx
    image: library/nginx:1.17-alpine
    ports:
    - containerPort: 80
    volumeMounts:
      - mountPath: "/var/www/html"
        name: data
  volumes:
    - name: data
      persistentVolumeClaim:
        claimName: my-pv-claim

Check that PersistentVolumeClaim has been created:
```
kubectl get pvc
```

Delete a persistent volume⁠

If you no longer need the persistent volume, delete the PersistentVolumeClaim that was used to create the volume.

The PV will be immediately deleted if the persistentVolumeReclaimPolicy: Delete parameter is specified in the PVC manifest. For more information about the Reclaim policy, see the Reclaiming Kubernetes documentation article.

Check which pods are bound to the PVC:
```
kubectl describe pvc <pvc_name>
```
Specify <pvc_name> is the name of the PersistentVolumeClaim.
Remove pods that use PVC:
```
kubectl delete pod <pod_name>
```
Specify <pod_name> is the name of the pod.
Delete the PVC to which the PV is bound:
```
kubectl delete pvc <pvc_name>
```
Specify <pvc_name> is the name of the PersistentVolumeClaim.

Permanent volumes

Create a permanent volume⁠​

1. Create StorageClass⁠​

StorageClass type⁠​

2. Create a PersistentVolumeClaim⁠​

3. Create a sub with a persistent volume⁠​

Increase the permanent volume⁠​

1. Check the amount of occupied space in the PVC⁠​

2. Check quotas⁠​

3. Allow permanent volume enlargement⁠​

4. Delete pods with the volume to be enlarged⁠​

5. Modify the PersistentVolumeClaim manifest⁠​

Delete a persistent volume⁠​

Create a permanent volume⁠

1. Create StorageClass⁠

StorageClass type⁠

2. Create a PersistentVolumeClaim⁠

3. Create a sub with a persistent volume⁠

Increase the permanent volume⁠

1. Check the amount of occupied space in the PVC⁠

2. Check quotas⁠

3. Allow permanent volume enlargement⁠

4. Delete pods with the volume to be enlarged⁠

5. Modify the PersistentVolumeClaim manifest⁠

Delete a persistent volume⁠