6.4. Using Persistent Volumes for Kubernetes Pods¶

6.4.1.1. Creating Storage Class¶

Сlick + Create on the Kubernetes dashboard and specify a YAML file that defines this object. For example:

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
  name: mysc
provisioner: cinder.csi.openstack.org
parameters:
  type: default

This manifest describes the storage class mysc with the storage policy default. The storage policy must exist in the compute cluster and be specified in the storage quotas to the current project.

6.4.2.1. Provisioning PV to Pod Dynamically¶

1. Access the Kubernetes cluster via the dashboard. Click Kubernetes access for instructions.

2. On the Kubernetes dashboard, create a storage class, as described in Creating Storage Classes.

3. Create a persistent volume claim. To do it, click + Create and specify the following YAML file:

   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
     name: mypvc
   spec:
     accessModes:
     - ReadWriteOnce
     resources:
         requests:
           storage: 10Gi
     storageClassName: mysc
   

   This manifest specifies the persistent volume claim mypvc that requests from the storage class mysc a volume of at least 10 GiB that can be mounted in the read/write mode by a single node.

   Creation of the PVC triggers dynamic provisioning of a persistent volume that satisfies the claim’s requirements. Kubernetes then binds it to the claim.

   

4. Create a pod and specify the PVC as its volume. To do it, click + Create and enter the following YAML file:

   apiVersion: v1
   kind: Pod
   metadata:
     name: nginx
   spec:
     containers:
     - image: nginx
       imagePullPolicy: IfNotPresent
       name: nginx
       ports:
       - containerPort: 80
         protocol: TCP
       volumeMounts:
         - mountPath: /var/lib/www/html
           name: mydisk
     volumes:
     - name: mydisk
       persistentVolumeClaim:
         claimName: mypvc
         readOnly: false
   

This configuration file describes the pod nginx that uses the persistent volume claim mypvc. The persistent volume bound to the claim will be accessible at /var/lib/www/html inside the nginx container.

6.4.3.1. Mounting Compute Volume¶

1. In the self-service panel, obtain the ID of the desired volume.

   

2. Access the Kubernetes cluster via the dashboard. Click Kubernetes access for instructions.

3. On the Kubernetes dashboard, create a storage class, as described in Creating Storage Classes.

4. Create a persistent volume. To do it, click + Create and specify the following YAML file:

   apiVersion: v1
   kind: PersistentVolume
   metadata:
     annotations:
       pv.kubernetes.io/provisioned-by: cinder.csi.openstack.org
     name: mypv
   spec:
     accessModes:
     - ReadWriteOnce
     capacity:
       storage: 10Gi
     csi:
       driver: cinder.csi.openstack.org
       fsType: ext4
       volumeHandle: c5850e42-4f9d-42b5-9bee-8809dedae424
     persistentVolumeReclaimPolicy: Delete
     storageClassName: mysc
   

   This manifest specifies the persistent volume mypv from the storage class mysc that has 10 GiB of storage and access mode that allows it to be mounted in the read/write mode by a single node. The PV mypv uses the compute volume with the ID c5850e42-4f9d-42b5-9bee-8809dedae424 as backing storage.

5. Create a persistent volume claim. Before you define the PVC, make sure the PV is created and has the status “Available”. The existing PV must meet the claim’s requirements to storage size, access mode and storage class. Click + Create and specify the following YAML file:

   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
     name: mypvc
   spec:
     accessModes:
     - ReadWriteOnce
     resources:
       requests:
         storage: 10Gi
     storageClassName: mysc
   

   Once the persistent volume claim mypvc is created, the volume mypv is bound to it.

   

6. Create a pod and specify the PVC as its volume. Use the example from Step 4 in Dynamically Provisioning Persistent Volumes.

   In the self-service panel, the compute volume will be mounted to the virtual machine running the Kubernetes pod.

   

6.4.4.1. Terminating Stuck Pod¶

Add the following lines to the spec section of the deployment configuration file:

terminationGracePeriodSeconds: 0
tolerations:
- effect: NoExecute
key: node.kubernetes.io/unreachable
operator: Exists
tolerationSeconds: 2
- effect: NoExecute
key: node.kubernetes.io/not-ready
operator: Exists
tolerationSeconds: 2

If the node’s state changes to “NotReady” or “Unreachable”, the pod will be automatically terminated in 2 seconds.

The entire YAML file of a deployment may look as follows:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: nginx
spec:
  replicas: 1
  selector:
    matchLabels:
      app: nginx
  template:
    metadata:
      labels:
        app: nginx
    spec:
      terminationGracePeriodSeconds: 0
      tolerations:
      - effect: NoExecute
        key: node.kubernetes.io/unreachable
        operator: Exists
        tolerationSeconds: 2
      - effect: NoExecute
        key: node.kubernetes.io/not-ready
        operator: Exists
        tolerationSeconds: 2
      containers:
      - image: nginx
        imagePullPolicy: IfNotPresent
        name: nginx
        ports:
        - containerPort: 80
          protocol: TCP
        volumeMounts:
          - mountPath: /var/lib/www/html
            name: mydisk
      volumes:
        - name: mydisk
          persistentVolumeClaim:
            claimName: mypvc

The manifest above describes the deployment nginx with one pod that uses the persistent volume claim mypvc and will be automatically terminated in 2 seconds in the event of node failure.