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Version: 3.2

Snapshot group of PVCs in airgapped bare metal

Summary and Key concepts

Summary:​

This article provides a comprehensive guide on creating and managing group snapshots of Portworx volumes in Kubernetes using the GroupVolumeSnapshot Custom Resource Definition (CRD). It covers prerequisites such as ensuring Stork is installed and operational, and explains how to create group snapshots for multiple PVCs, track snapshot status, and restore PVCs from the snapshots. The document also details how to set pre- and post-snapshot rules to manage application behavior during snapshot operations. It includes an example of taking group snapshots for Cassandra PVCs and restoring them, along with instructions for managing cross-namespace snapshots.

Kubernetes Concepts:​

  • PersistentVolumeClaim (PVC): A user request for storage in Kubernetes, used for creating and restoring group snapshots.
  • StorageClass: Defines how storage is dynamically provisioned for PVCs and snapshots.
  • Annotations: Used to add metadata to objects such as PVCs and snapshots, including cross-namespace snapshot restoration.
  • StatefulSet: Manages the deployment of stateful applications, ensuring each pod maintains a stable identity.

Portworx Concepts:​

  • Stork: A Portworx extension that handles advanced data management operations such as snapshots and backups in Kubernetes.

  • VolumeSnapshot: A snapshot of a Portworx volume that can be used for backup and recovery.

This document will show you how to create group snapshots of Portworx volumes and how you can restore those snapshots to use them in pods.

Pre-requisites​

Installing Stork​

This requires that you already have Stork installed and running on your Kubernetes cluster. If you fetched the Portworx specs from the Portworx spec generator in Portworx Central and used the default options, Stork is already installed.

Creating group snapshots​

To take group snapshots, you need to use the GroupVolumeSnapshot CRD object. Here is a simple example:

apiVersion: stork.libopenstorage.org/v1alpha1
kind: GroupVolumeSnapshot
metadata:
  name: cassandra-groupsnapshot
spec:
  pvcSelector:
    matchLabels:
      app: cassandra

Above spec will take a group snapshot of all PVCs that match labels app=cassandra.

The Examples section has a more detailed end-to-end example.

The GroupVolumeSnapshot object also supports specifying pre and post rules that are run on the application pods using the volumes being snapshotted. This allows users to quiesce the applications before the snapshot is taken and resume I/O after the snapshot is taken. Refer to 3D Snapshots for more detailed documentation on that.

Checking status of group snapshots​

A new VolumeSnapshot object will get created for each PVC that matches the given pvcSelector. For example, if the label selector app: cassandra matches 3 PVCs, you will have 3 volumesnapshot objects.

You can track the status of the group volume snapshots using:

kubectl describe groupvolumesnapshot <group-snapshot-name>

This will show the latest status and will also list the VolumeSnapshot objects once it's complete. Below is an example of the status section of the cassandra group snapshot.

Status:
  Stage:   Final
  Status:  Successful
  Volume Snapshots:
    Conditions:
      Last Transition Time:  2019-01-14T18:02:47Z
      Message:               Snapshot created successfully and it is ready
      Reason:
      Status:                True
      Type:                  Ready
    Data Source:
      Portworx Volume:
        Snapshot Id:       1015874155818710382
    Parent Volume ID:      763613271174793816
    Task ID:
    Volume Snapshot Name:  cassandra-group-snapshot-cassandra-data-cassandra-2-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
    Conditions:
      Last Transition Time:  2019-01-14T18:02:47Z
      Message:               Snapshot created successfully and it is ready
      Reason:
      Status:                True
      Type:                  Ready
    Data Source:
      Portworx Volume:
        Snapshot Id:       1130064992705573378
    Parent Volume ID:      1081147806034223862
    Task ID:
    Volume Snapshot Name:  cassandra-group-snapshot-cassandra-data-cassandra-0-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
    Conditions:
      Last Transition Time:  2019-01-14T18:02:47Z
      Message:               Snapshot created successfully and it is ready
      Reason:
      Status:                True
      Type:                  Ready
    Data Source:
      Portworx Volume:
        Snapshot Id:       175241555565145805
    Parent Volume ID:      237262101530372284
    Task ID:
    Volume Snapshot Name:  cassandra-group-snapshot-cassandra-data-cassandra-1-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7

You can see 3 VolumeSnapshots which are part of the group snapshot. The name of the VolumeSnapshot is in the Volume Snapshot Name field. For more details on the VolumeSnapshot, you can do:

kubectl get volumesnapshot.volumesnapshot.external-storage.k8s.io/<volume-snapshot-name> -o yaml

Snapshots across namespaces​

When creating a group snapshot, you can specify a list of namespaces to which the group snapshot can be restored. Below is an example of a group snapshot which can be restored into prod-01 and prod-02 namespaces.

apiVersion: stork.libopenstorage.org/v1alpha1
kind: GroupVolumeSnapshot
metadata:
  name: cassandra-groupsnapshot
spec:
  pvcSelector:
    matchLabels:
      app: cassandra
  restoreNamespaces:
   - prod-01
   - prod-02

Restoring from group snapshots​

Previous section describes how to list the volume snapshots that are part of a group snapshot. Once you have the names the VolumeSnapshot objects, you can use them to create PVCs from them.

When you install Stork, it also creates a storage class called stork-snapshot-sc. This storage class can be used to create PVCs from snapshots.

To create a PVC from a snapshot, add the snapshot.alpha.kubernetes.io/snapshot annotation to refer to the snapshot name. If the snapshot exists in another namespace, you should specify the snapshot namespace with the stork.libopenstorage.org/snapshot-source-namespace annotation in the PVC.

The Retain policy is important if you need to keep the volume in place, even after removing the Kubernetes objects from a cluster.

note
  • As shown in the following example, the storageClassName should be the Stork StorageClass stork-snapshot-sc.
  • When using this storage class the PVC is creating with delete as Retain policy. However, if the source PVC is having the policy as retain, then this will not be inherited to the restored PVC. After the restore, you should manually verify the retain policy and change it if needed.
apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: mysql-snap-clone
  annotations:
    snapshot.alpha.kubernetes.io/snapshot: mysql-snapshot
spec:
  accessModes:
     - ReadWriteOnce
  storageClassName: stork-snapshot-sc
  resources:
    requests:
      storage: 2Gi

Once you apply the above spec, you will see a PVC created by Stork. This PVC will be backed by a Portworx volume clone of the snapshot created above.

kubectl get pvc

NAMESPACE   NAME                                   STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS                AGE
default     mysql-data                             Bound     pvc-xxxxxxxx-xxxx-xxxx-xxxx-0214683e8447   2Gi        RWO            px-mysql-sc                 2d
default     mysql-snap-clone                       Bound     pvc-xxxxxxxx-xxxx-xxxx-xxxx-0214683e8447   2Gi        RWO            stork-snapshot-sc           2s

Examples​

Group snapshot for all cassandra PVCs​

In below example, we will take a group snapshot for all PVCs in the default namespace and that have labels app: cassandra.

Step 1: Deploy cassandra statefulset and PVCs​

Following spec creates a replica 3 cassandra statefulset. Each replica pod will use its own PVC.

##### Portworx storage class
kind: StorageClass
apiVersion: storage.k8s.io/v1
metadata:
  name: portworx-repl2
provisioner: pxd.portworx.com
parameters:
  repl: "2"
---
apiVersion: v1
kind: Service
metadata:
  labels:
    app: cassandra
  name: cassandra
spec:
  clusterIP: None
  ports:
    - port: 9042
  selector:
    app: cassandra

---

apiVersion: "apps/v1"
kind: StatefulSet
metadata:
  name: cassandra
spec:
  selector:
    matchLabels:
      app: cassandra
  serviceName: cassandra
  replicas: 3
  template:
    metadata:
      labels:
        app: cassandra
    spec:
      containers:
      - name: cassandra
        image: gcr.io/google-samples/cassandra:v12
        imagePullPolicy: Always
        ports:
        - containerPort: 7000
          name: intra-node
        - containerPort: 7001
          name: tls-intra-node
        - containerPort: 7199
          name: jmx
        - containerPort: 9042
          name: cql
        resources:
          limits:
            cpu: "500m"
            memory: 1Gi
          requests:
           cpu: "500m"
           memory: 1Gi
        securityContext:
          capabilities:
            add:
              - IPC_LOCK
        lifecycle:
          preStop:
            exec:
              command: ["/bin/sh", "-c", "PID=$(pidof java) && kill $PID && while ps -p $PID > /dev/null; do sleep 1; done"]
        env:
          - name: MAX_HEAP_SIZE
            value: 512M
          - name: HEAP_NEWSIZE
            value: 100M
          - name: CASSANDRA_SEEDS
            value: "cassandra-0.cassandra.default.svc.cluster.local"
          - name: CASSANDRA_CLUSTER_NAME
            value: "K8Demo"
          - name: CASSANDRA_DC
            value: "DC1-K8Demo"
          - name: CASSANDRA_RACK
            value: "Rack1-K8Demo"
          - name: CASSANDRA_AUTO_BOOTSTRAP
            value: "false"
          - name: POD_IP
            valueFrom:
              fieldRef:
                fieldPath: status.podIP
          - name: POD_NAMESPACE
            valueFrom:
              fieldRef:
                fieldPath: metadata.namespace
        readinessProbe:
          exec:
            command:
            - /bin/bash
            - -c
            - /ready-probe.sh
          initialDelaySeconds: 15
          timeoutSeconds: 5
        # These volume mounts are persistent. They are like inline claims,
        # but not exactly because the names need to match exactly one of
        # the stateful pod volumes.
        volumeMounts:
        - name: cassandra-data
          mountPath: /cassandra_data
  # These are converted to volume claims by the controller
  # and mounted at the paths mentioned above.
  volumeClaimTemplates:
  - metadata:
      name: cassandra-data
      labels:
        app: cassandra
      annotations:
        volume.beta.kubernetes.io/storage-class: portworx-repl2
    spec:
      accessModes: [ "ReadWriteOnce" ]
      resources:
        requests:
          storage: 2Gi

Step 2: Wait for all cassandra pods to be running​

List the cassandra pods:

kubectl get pods -l app=cassandra

NAME          READY     STATUS    RESTARTS   AGE
cassandra-0   1/1       Running   0          3m
cassandra-1   1/1       Running   0          2m
cassandra-2   1/1       Running   0          1m

Once you see all the 3 pods, you can also list the cassandra PVCs.

kubectl get pvc -l app=cassandra

NAME                         STATUS    VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS        AGE
cassandra-data-cassandra-0   Bound     pvc-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7   2Gi        RWO            stork-snapshot-sc   3m
cassandra-data-cassandra-1   Bound     pvc-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7   2Gi        RWO            stork-snapshot-sc   2m
cassandra-data-cassandra-2   Bound     pvc-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7   2Gi        RWO            stork-snapshot-sc   1m

Step 3: Take the group snapshot​

Apply the following spec to take the cassandra group snapshot. Portworx will quiesce I/O on all volumes before triggering their snapshots.

apiVersion: stork.libopenstorage.org/v1alpha1
kind: GroupVolumeSnapshot
metadata:
  name: cassandra-group-snapshot
spec:
  pvcSelector:
    matchLabels:
      app: cassandra

Once you apply the above object you can check the status of the snapshots using kubectl:

kubectl describe groupvolumesnapshot cassandra-group-snapshot

While the group snapshot is in progress, the status will reflect as InProgress. Once complete, you should see a status stage as Final and status as Successful.

Name:         cassandra-group-snapshot
Namespace:    default
Labels:       <none>
Annotations:  kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"stork.libopenstorage.org/v1alpha1","kind":"GroupVolumeSnapshot","metadata":{"annotations":{},"name":"cassandra-group-snapshot"
,"namespac...
API Version:  stork.libopenstorage.org/v1alpha1
Kind:         GroupVolumeSnapshot
Metadata:
  Cluster Name:
  Creation Timestamp:  2019-01-14T18:02:16Z
  Generation:          0
  Resource Version:    18184467
  Self Link:           /apis/stork.libopenstorage.org/v1alpha1/namespaces/default/groupvolumesnapshots/cassandra-group-snapshot
  UID:                 xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
Spec:
  Options:             <nil>
  Post Snapshot Rule:
  Pre Snapshot Rule:
  Pvc Selector:
    Match Labels:
      App:  cassandra
Status:
  Stage:   Final
  Status:  Successful
  Volume Snapshots:
    Conditions:
      Last Transition Time:  2019-01-14T18:02:47Z
      Message:               Snapshot created successfully and it is ready
      Reason:
      Status:                True
      Type:                  Ready
    Data Source:
      Portworx Volume:
        Snapshot Id:       1015874155818710382
    Parent Volume ID:      763613271174793816
    Task ID:
    Volume Snapshot Name:  cassandra-group-snapshot-cassandra-data-cassandra-2-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
    Conditions:
      Last Transition Time:  2019-01-14T18:02:47Z
      Message:               Snapshot created successfully and it is ready
      Reason:
      Status:                True
      Type:                  Ready
    Data Source:
      Portworx Volume:
        Snapshot Id:       1130064992705573378
    Parent Volume ID:      1081147806034223862
    Task ID:
    Volume Snapshot Name:  cassandra-group-snapshot-cassandra-data-cassandra-0-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
    Conditions:
      Last Transition Time:  2019-01-14T18:02:47Z
      Message:               Snapshot created successfully and it is ready
      Reason:
      Status:                True
      Type:                  Ready
    Data Source:
      Portworx Volume:
        Snapshot Id:       175241555565145805
    Parent Volume ID:      237262101530372284
    Task ID:
    Volume Snapshot Name:  cassandra-group-snapshot-cassandra-data-cassandra-1-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7                  16s

Above we can see that creation of cassandra-group-snapshot created 3 volumesnapshots:

  1. cassandra-group-snapshot-cassandra-data-cassandra-0-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
  2. cassandra-group-snapshot-cassandra-data-cassandra-1-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
  3. cassandra-group-snapshot-cassandra-data-cassandra-2-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7

These correspond to the PVCs cassandra-data-cassandra-0, cassandra-data-cassandra-1 and cassandra-data-cassandra-2 respectively.

You can also describe these individual volume snapshots using

 kubectl describe volumesnapshot cassandra-group-snapshot-cassandra-data-cassandra-0-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7

Name:         cassandra-group-snapshot-cassandra-data-cassandra-0-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
Namespace:    default
Labels:       <none>
Annotations:  <none>
API Version:  volumesnapshot.external-storage.k8s.io/v1
Kind:         VolumeSnapshot
Metadata:
  Cluster Name:
  Creation Timestamp:  2019-01-14T18:02:47Z
  Owner References:
    API Version:     stork.libopenstorage.org/v1alpha1
    Kind:            GroupVolumeSnapshot
    Name:            cassandra-group-snapshot
    UID:             xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
  Resource Version:  18184459
  Self Link:         /apis/volumesnapshot.external-storage.k8s.io/v1/namespaces/default/volumesnapshots/cassandra-group-snapshot-cassandra-data-cassandra-0-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
  UID:               xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
Spec:
  Persistent Volume Claim Name:  cassandra-data-cassandra-0
  Snapshot Data Name:            cassandra-group-snapshot-cassandra-data-cassandra-0-xxxxxxxx-xxxx-xxxx-xxxx-080027ee1df7
Status:
  Conditions:
    Last Transition Time:  2019-01-14T18:02:47Z
    Message:               Snapshot created successfully and it is ready
    Reason:
    Status:                True
    Type:                  Ready
  Creation Timestamp:      <nil>
Events:                    <none>

Deleting group snapshots​

To delete group snapshots, you need to delete the GroupVolumeSnapshot that was used to create the group snapshots. Stork will delete all other volumesnapshots that were created for this group snapshot.

kubectl delete groupvolumesnapshot cassandra-group-snapshot

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