exercise-8

Exercise 8 - Cloning and Restoring a Snapshot

Cloning and Restoring a Snapshot

After creating a snapshot, you can restore it to a new Persitent Volume Claim. To do this you must create a special StorageClass implemented by snapshot-provisioner. We will then create a PersistentVolumeClaim referencing this StorageClass for dynamically provisioning new PersistentVolume. An annotation on the PersistentVolumeClaim will inform snapshot-provisioner about where to find the information it needs to deal with the OpenEBS API Server to restore the snapshot.

A StorageClass can be defined as in the following example. Here, the provisioner field defines which provisioner should be used and what parameters should be passed to that provisioner when dynamic provisioning is invoked.

Such a StorageClass is necessary for restoring a Persistent Volume from an already created Volume Snapshot and Volume Snapshot Data.

Create a Storage Class to restore from Snapshot

1. Create the storageclass YAML file:

   nano openebs-restore-storageclass.yaml
   

2. Paste the content and save.

   kind: StorageClass
   apiVersion: storage.k8s.io/v1
   metadata:
     name: snapshot-promoter
   provisioner: volumesnapshot.external-storage.k8s.io/snapshot-promoter
   

   annotations: snapshot.alpha.kubernetes.io/snapshot: the name of the Volume Snapshot that will be restored. storageClassName: Storage Class created by the admin for restoring Volume Snapshots.

3. Once the openebs-restore-storageclass is created, you have to deploy the YAML by using the following command.

   kubectl apply -f openebs-restore-storageclass.yaml
   

Restore from Snapshot

You can now create a PersistentVolumeClaim that will use the StorageClass to dynamically provision a PersistentVolume that contains the information of your snapshot. Create a YAML file that will delpoy a PersistentVolumeClaim using the following details.

1. Create the Persistent Volume Claim YAML file:

   nano restore-pvc.yaml
   

2. Paste the content and save.

   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
     name: demo-snap-vol-claim
     annotations:
       snapshot.alpha.kubernetes.io/snapshot: snapshot-blue
   spec:
     storageClassName: snapshot-promoter
     accessModes: ReadWriteOnce
     resources:
       requests:
         storage: 1G
   

3. Once the restore-pvc.yaml is created, you have to deploy the YAML by using the following command.

   kubectl apply -f restore-pvc.yaml
   

4. Finally mount the demo-snap-vol-claim PersistentVolumeClaim into a green pod to see that the snapshot was restored. While deploying the green pod, you have to edit the deplyment YAML and mention the restore PersistentVolumeClaim name, volume name, and mountPath accordingly. An example for your reference is given below.

5. Paste the content and save.

   apiVersion: v1
   kind: Pod
   metadata:
     name: green
   spec:
     restartPolicy: Never
     containers:
     - name: green
       image: busybox
       command:
       - "/bin/sh"
       - "-c"
       - "while true; do date >> /tmp/pod-out.txt; sleep 1; done"
       volumeMounts:
       - name: demo-snap-vol1
         mountPath: /tmp
     volumes:
       - name: demo-snap-vol1
         persistentVolumeClaim:
           claimName: demo-snap-vol-claim
   ---
   
   

6. Once green.yaml is created, you can deploy the YAML by using the following command:

   kubectl apply -f green.yaml
   

7. List pods and verify green pod is running.

   $ kubectl get pods
   NAME                                                             READY     STATUS    RESTARTS   AGE
   alertmanager-79fc4b59db-82zmr                                    1/1       Running   0          21h
   blue                                                             1/1       Running   0          20h
   grafana-7688b94dc-lr578                                          1/1       Running   0          21h
   green                                                            1/1       Running   0          2m
   node-exporter-6gtgx                                              1/1       Running   0          21h
   node-exporter-btdp8                                              1/1       Running   0          21h
   node-exporter-k5v6t                                              1/1       Running   0          21h
   prometheus-deployment-78cd57c5d7-q4sbl                           1/1       Running   0          21h
   pvc-b6cd585c-73e8-11e8-9f52-06731769042c-ctrl-546ddc8969-f9s97   2/2       Running   0          6m
   pvc-b6cd585c-73e8-11e8-9f52-06731769042c-rep-699f4948c5-bmgdn    1/1       Running   0          6m
   pvc-b6cd585c-73e8-11e8-9f52-06731769042c-rep-699f4948c5-djmv6    1/1       Running   1          6m
   pvc-b6cd585c-73e8-11e8-9f52-06731769042c-rep-699f4948c5-thl82    1/1       Running   0          6m
   pvc-d2e08c54-733e-11e8-9f52-06731769042c-ctrl-949dd445f-czm2b    2/2       Running   0          20h
   pvc-d2e08c54-733e-11e8-9f52-06731769042c-rep-878485f7-qnvd9      1/1       Running   0          20h
   pvc-d2e08c54-733e-11e8-9f52-06731769042c-rep-878485f7-s5nsn      1/1       Running   0          20h
   pvc-d2e08c54-733e-11e8-9f52-06731769042c-rep-878485f7-xmdpc      1/1       Running   0          20h
   

8. List persistent volumes and verify that demo-snap-vol-claim exist claimed by the snapshot-promoter.

   $ kubectl get pv
   NAME                                       CAPACITY   ACCESS MODES   RECLAIM POLICY   STATUS    CLAIM                         STORAGECLASS        REASON    AGE
   pvc-2dcb6cfd-733a-11e8-9f52-06731769042c   400M       RWO            Delete           Bound     default/pgdata-pgset-1        openebs-standard              20h
   pvc-b6cd585c-73e8-11e8-9f52-06731769042c   1G         RWO            Delete           Bound     default/demo-snap-vol-claim   snapshot-promoter             5m
   pvc-d2e08c54-733e-11e8-9f52-06731769042c   1G         RWO            Delete           Bound     default/demo-vol1-claim       openebs-standard              20h
   

9. Once the green pod is in running state, you can check the integrity of files which were created earlier before taking the snapshot.

   $ kubectl exec -it green cat /tmp/pod-out.txt
   ...
   Mon Jun 18 21:31:19 UTC 2018
   Mon Jun 18 21:31:20 UTC 2018
   Mon Jun 18 21:31:21 UTC 2018
   ...
   

Continue to Exercise 9 - Rollout your application with Blue/Green deployment