Populating volumes of a StatefulSet

This guide will show you how to use KubeStash to populate the volumes of a StatefulSet. We’ll walk through backing up the volumes of a Statefulset and then restoring the backed up data to a new StatefulSet in a Kubernetes-native way with KubeStash.

Before You Begin

At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using kind.
Install KubeStash in your cluster following the steps here.
You should be familiar with the following KubeStash concepts:

To keep everything isolated, we are going to use a separate namespace called demo throughout this tutorial.

$ kubectl create ns demo
namespace/demo created

Note: YAML files used in this tutorial are stored in docs/guides/volume-populator/statefulset/examples directory of kubestash/docs repository.

Prepare Workload

At first, We are going to deploy a StatefulSet with a PVC. This StatefulSet will automatically generate sample data in /source/data directory.

Below is the YAML of the StatefulSet that we are going to create,

apiVersion: v1
kind: Service
metadata:
  name: busybox
  namespace: demo
spec:
  ports:
    - name: http
      port: 80
      targetPort: 0
  selector:
    app: demo-busybox
  clusterIP: None
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: sample-sts
  namespace: demo
  labels:
    app: demo-busybox
spec:
  replicas: 3
  selector:
    matchLabels:
      app: demo-busybox
  serviceName: busybox
  template:
    metadata:
      labels:
        app: demo-busybox
    spec:
      containers:
        - name: busybox
          image: busybox
          command: ["/bin/sh", "-c","echo $(POD_NAME) > /source/data/data.txt && sleep 3000"]
          env:
            - name: POD_NAME
              valueFrom:
                fieldRef:
                  fieldPath: metadata.name
          volumeMounts:
            - name: source-data
              mountPath: "/source/data"
          imagePullPolicy: IfNotPresent
  volumeClaimTemplates:
    - metadata:
        name: source-data
      spec:
        accessModes: [ "ReadWriteOnce" ]
        resources:
          requests:
            storage: 256Mi

Let’s create the StatefulSet we have shown above.

$ kubectl apply -f https://github.com/kubestash/docs/raw/v2024.8.14/docs/guides/volume-populator/statefulset/examples/statefulset.yaml
service/busybox created
statefulset.apps/sample-sts created

Now, wait for the pods of the StatefulSet to go into the Running state.

$ kubectl get pod -n demo
NAME           READY   STATUS    RESTARTS   AGE
sample-sts-0   1/1     Running   0          42s
sample-sts-1   1/1     Running   0          40s
sample-sts-2   1/1     Running   0          36s

Verify that the sample data has been generated in /source/data directory for sample-sts-0 , sample-sts-1 and sample-sts-2 pod respectively using the following commands,

$ kubectl exec -n demo sample-sts-0 -- cat /source/data/data.txt
sample-sts-0
$ kubectl exec -n demo sample-sts-1 -- cat /source/data/data.txt
sample-sts-1
$ kubectl exec -n demo sample-sts-2 -- cat /source/data/data.txt
sample-sts-2

Prepare Backend

Now, we are going to backup the StatefulSet sample-sts to a GCS bucket using KubeStash. For this, we have to create a Secret with necessary credentials and a BackupStorage object. If you want to use a different backend, please read the respective backend configuration doc from here.

For GCS backend, if the bucket does not exist, KubeStash needs Storage Object Admin role permissions to create the bucket. For more details, please check the following guide.

Create Secret:

Let’s create a Secret named gcs-secret with access credentials of our desired GCS backend,

$ echo -n '<your-project-id>' > GOOGLE_PROJECT_ID
$ cat /path/to/downloaded/sa_key_file.json > GOOGLE_SERVICE_ACCOUNT_JSON_KEY
$ kubectl create secret generic -n demo gcs-secret \
    --from-file=./GOOGLE_PROJECT_ID \
    --from-file=./GOOGLE_SERVICE_ACCOUNT_JSON_KEY
secret/gcs-secret created

Create BackupStorage:

Now, create a BackupStorage custom resource specifying the desired bucket, and directory inside the bucket where the backed up data will be stored.

Below is the YAML of BackupStorage object that we are going to create,

apiVersion: storage.kubestash.com/v1alpha1
kind: BackupStorage
metadata:
  name: gcs-storage
  namespace: demo
spec:
  storage:
    provider: gcs
    gcs:
      bucket: kubestash-qa
      prefix: demo
      secretName: gcs-secret
  usagePolicy:
    allowedNamespaces:
      from: All
  default: true 
  deletionPolicy: WipeOut

Let’s create the BackupStorage object that we have shown above,

$ kubectl apply -f https://github.com/kubestash/docs/raw/v2024.8.14/docs/guides/volume-populator/statefulset/examples/backupstorage.yaml
backupstorage.storage.kubestash.com/gcs-storage created

Now, we are ready to backup our target volume to this backend.

Create RetentionPolicy:

Now, we have to create a RetentionPolicy object to specify how the old Snapshots should be cleaned up.

Below is the YAML of the RetentionPolicy object that we are going to create,

apiVersion: storage.kubestash.com/v1alpha1
kind: RetentionPolicy
metadata:
  name: demo-retention
  namespace: demo
spec:
  default: true
  failedSnapshots:
    last: 2
  maxRetentionPeriod: 2mo
  successfulSnapshots:
    last: 5
  usagePolicy:
    allowedNamespaces:
      from: Same

Notice the spec.usagePolicy that allows referencing the RetentionPolicy from all namespaces.For more details on configuring it for specific namespaces, please refer to the following RetentionPolicy usage policy.

Let’s create the RetentionPolicy object that we have shown above,

$ kubectl apply -f https://github.com/kubestash/docs/raw/v2024.8.14/docs/guides/volume-populator/statefulset/examples/retentionpolicy.yaml
retentionpolicy.storage.kubestash.com/demo-retention created

Backup

Now, we have to create a BackupConfiguration custom resource targeting the sample-tst StatefulSet that we have created earlier.

We also have to create another Secret with an encryption key RESTIC_PASSWORD for Restic. This secret will be used by Restic for both encrypting and decrypting the backup data during backup & restore.

Create Secret:

Let’s create a secret called encrypt-secret with the Restic password,

$ echo -n 'changeit' > RESTIC_PASSWORD
$ kubectl create secret generic -n demo encrypt-secret \
    --from-file=./RESTIC_PASSWORD \
secret "encrypt-secret" created

Create BackupConfiguration:

Below is the YAML of the BackupConfiguration object that we are going to create,

apiVersion: core.kubestash.com/v1alpha1
kind: BackupConfiguration
metadata:
  name: sample-backup-sts
  namespace: demo
spec:
  target:
    apiGroup: apps
    kind: StatefulSet
    name: sample-sts
    namespace: demo
  backends:
    - name: gcs-backend
      storageRef:
        name: gcs-storage
        namespace: demo
      retentionPolicy:
        name: demo-retention
        namespace: demo
  sessions:
    - name: demo-session
      scheduler:
        schedule: "*/5 * * * *"
        jobTemplate:
          backoffLimit: 1
      repositories:
        - name: gcs-demo-repo
          backend: gcs-backend
          directory: /sample-sts
          encryptionSecret:
            name: encrypt-secret
            namespace: demo
      addon:
        name: workload-addon
        tasks:
          - name: logical-backup
            params:
              paths: /source/data
              exclude: /source/data/lost+found
      retryConfig:
        maxRetry: 2
        delay: 1m

Let’s create the BackupConfiguration object we have shown above,

$ kubectl apply -f https://github.com/kubestash/docs/raw/v2024.8.14/docs/guides/volume-populator/statefulset/examples/backupconfiguration.yaml
backupconfiguration.core.kubestash.com/sample-backup-sts created

Verify Backup Setup Successful

If everything goes well, the phase of the BackupConfiguration should be in Ready state. The Ready phase indicates that the backup setup is successful.

Let’s check the Phase of the BackupConfiguration

$ kubectl get backupconfiguration -n demo
NAME                PHASE   PAUSED   AGE
sample-backup-sts   Ready            2m50s

Verify Repository:

Verify that the Repository specified in the BackupConfiguration has been created using the following command,

$ kubectl get repositories -n demo
NAME             INTEGRITY   SNAPSHOT-COUNT   SIZE   PHASE   LAST-SUCCESSFUL-BACKUP   AGE
gcs-repository                                       Ready                            28s

KubeStash keeps the backup for Repository YAMLs. If we navigate to the GCS bucket, we will see the Repository YAML stored in the kubestash-qa/demo/sample-sts directory.

Verify CronJob:

Verify that KubeStash has created a CronJob with the schedule specified in spec.sessions[*].scheduler.schedule field of BackupConfiguration object.

Check that the CronJob has been created using the following command,

$ kubectl get cronjob -n demo
NAME                                     SCHEDULE      SUSPEND   ACTIVE   LAST SCHEDULE   AGE
trigger-sample-backup-sts-demo-session   */5 * * * *             0        2m45s           3m25s

Wait for BackupSession:

Now, wait for the next backup schedule. You can watch for BackupSession CR using the following command,

$ watch -n 1 kubectl get backupsession -n demo -l=kubestash.com/invoker-name=sample-backup-sts

Every 1.0s: kubectl get backupsession -n demo -l=kubestash.com/invoker-name=sample-backup-sts                                                                                           workstation: Wed Jan  3 17:26:00 2024

NAME                                            INVOKER-TYPE          INVOKER-NAME     PHASE       DURATION   AGE
sample-backup-sts-demo-session-1706015400       BackupConfiguration   pvc-backup       Succeeded              60s

Here, the phase Succeeded means that the backup process has been completed successfully.

Verify Backup:

When backup session is complete, KubeStash will update the respective Repository object to reflect the backup. Check that the repository gcs-repository has been updated by the following command,

$ kubectl get repository -n demo gcs-demo-repo
NAME              INTEGRITY   SNAPSHOT-COUNT   SIZE    PHASE   LAST-SUCCESSFUL-BACKUP   AGE
gcs-repository    true        1                806 B   Ready   8m27s                    9m18s

At this moment we have one Snapshot. Run the following command to check the respective Snapshot.

Verify created Snapshot object by the following command,

$ kubectl get snapshots -n demo -l=kubestash.com/repo-name=gcs-repository
NAME                                                          REPOSITORY      SESSION        SNAPSHOT-TIME          DELETION-POLICY   PHASE       AGE
gcs-repository-sample-backup-sts-frequent-backup-1706015400   gcs-demo-repo   demo-session   2024-01-23T13:10:54Z   Delete            Succeeded   16h

At this moment we have one Snapshot. Run the following command to check the respective Snapshot.

$ kubectl get snapshots -n demo -l=kubestash.com/repo-name=gcs-demo-repo
NAME                                                      REPOSITORY      SESSION        SNAPSHOT-TIME          DELETION-POLICY   PHASE       AGE
gcs-demo-repo-sample-backup-sts-demo-session-1706015400   gcs-demo-repo   demo-session   2024-01-23T13:10:54Z   Delete            Succeeded   16h

Note: KubeStash creates a Snapshot with the following labels:
kubestash.com/app-ref-kind: <target-kind>
kubestash.com/app-ref-name: <target-name>
kubestash.com/app-ref-namespace: <target-namespace>
kubestash.com/repo-name: <repository-name>
These labels can be used to watch only the Snapshots related to our desired Workload or Repository.

Now, lets retrieve the YAML for the Snapshot, and inspect the spec.status section to see the backup up components of the StatefulSet.

$ kubectl get snapshots -n demo gcs-demo-repo-sample-backup-sts-demo-session-1706015400 -oyaml

apiVersion: storage.kubestash.com/v1alpha1
kind: Snapshot
metadata:
  labels:
    kubestash.com/app-ref-kind: StatefulSet
    kubestash.com/app-ref-name: sample-sts
    kubestash.com/app-ref-namespace: demo
    kubestash.com/repo-name: gcs-demo-repo
  name: gcs-demo-repo-sample-backup-sts-demo-session-1706015400
  namespace: demo
spec:
  ...
status:
  components:
    dump-pod-0:
      driver: Restic
      duration: 1.61162906s
      integrity: true
      path: repository/v1/demo-session/dump-pod-0
      phase: Succeeded
      resticStats:
      - hostPath: /source/data
        id: 4e881fdd20afb49e1baab37654cc18d440dc2f90ad61c9077956ea4561bd41dd
        size: 13 B
        uploaded: 1.046 KiB
      size: 803 B
    dump-pod-1:
      driver: Restic
      duration: 1.597963671s
      integrity: true
      path: repository/v1/demo-session/dump-pod-1
      phase: Succeeded
      resticStats:
      - hostPath: /source/data
        id: 16a414187d554e1713c0a6363d904837998dc7f7d600d7c635a04c61dc1b5467
        size: 13 B
        uploaded: 1.046 KiB
      size: 803 B
    dump-pod-2:
      driver: Restic
      duration: 1.52695046s
      integrity: true
      path: repository/v1/demo-session/dump-pod-2
      phase: Succeeded
      resticStats:
      - hostPath: /source/data
        id: 9dc9efd5e9adfd0154eca48433cc57aa09bca018d970e9530769326c9783905c
        size: 13 B
        uploaded: 1.046 KiB
      size: 798 B
  ...

For StatefulSet, KubeStash takes backup from every pod of the StatefulSet. Since we are using three replicas, three components have been taken backup. The component name is dump-pod-<ordinal-value>. The ordinal value in the component’s name represents the ordinal value of the StatefulSet pod ordinal.

Populate Volumes

This section will show you how to populate the volumes of a StatefulSet with data from the Snapshot of the previous backup using KubeStash.

Deploy StatefulSet :

Now, we need to create a new StatefulSet along with a PersistentVolumeClaim (PVC) using VolumeClaimTemplates. This PVC configure with spec.dataSourceRef pointing to our Snapshot object. KubeStash will populate volume with the restored data from pointing snapshot and attach it to corresponding PVCs. As a result, this PVCs will contain the data that has been restored.

Below is the YAML of the restored StatefulSet,

apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: sample-restored-sts
  namespace: demo
  labels:
    app: demo-busybox
spec:
  replicas: 3
  selector:
    matchLabels:
      app: demo-busybox
  serviceName: busybox
  template:
    metadata:
      labels:
        app: demo-busybox
    spec:
      containers:
        - name: busybox
          image: busybox
          command: ["/bin/sh", "-c","sleep 3000"]
          volumeMounts:
            - name: restored-source-data
              mountPath: "/source/data"
          imagePullPolicy: IfNotPresent
  volumeClaimTemplates:
    - metadata:
        name: restored-source-data
        annotations:
          populator.kubestash.com/app-name: sample-restored-sts
      spec:
        accessModes: [ "ReadWriteOnce" ]
        resources:
          requests:
            storage: 256Mi
        dataSourceRef:
          apiGroup: storage.kubestash.com
          kind: Snapshot
          name: gcs-demo-repo-sample-backup-sts-demo-session-1707900900

Here,

spec.dataSourceRef specifies that which snapshot we want to use for restoring and populating the volume. We have referenced the Snapshot object that was backed up in the previous section.
metadata.annotations.populator.kubestash.com/app-name field is mandatory for any volume population of a StatefulSet through KubeStash.
- This field denotes the StatefulSet that will be attached those volumes via mount paths. The volume population will only be successful if the mount path of this volume matches the mount paths of the backup StatefulSet.

Let’s create the StatefulSet we have shown above.

$ kubectl apply -f https://github.com/kubestash/docs/raw/v2024.8.14/docs/guides/volume-populator/statefulset/examples/restore-statefulset.yaml
statefulset.apps/sample-restored-sts created

Wait for Populate Volume:

When StatefulSet create PVC with spec.dataSourceRef that refers our Snapshot object for each replica, KubeStash automatically creates a populator Job. Now, just wait for the volume population process to finish.

You can watch the PVCs status using the following command,

$ watch kubectl get pvc -n demo 

Every 2.0s: kubectl get pvc -n demo                                                                   anisur: Tue Feb 13 18:37:26 2024

NAME                                         STATUS   VOLUME                                     CAPACITY   ACCESS MODES   STORAGECLASS   AGE
restored-source-data-sample-restored-sts-0   Bound    pvc-1fb1df97-6c36-4dd3-9b30-be5307abba60   1Gi        RWO            standard-rwo   2m46s
restored-source-data-sample-restored-sts-1   Bound    pvc-4726726d-7f9d-4c67-8aa2-57615b88a989   1Gi        RWO            standard-rwo   2m25s
restored-source-data-sample-restored-sts-2   Bound    pvc-df60d50f-9697-4d2f-a6e2-9e9c7ea89524   1Gi        RWO            standard-rwo   2m3s

The output of the command shows the PVCs status as Bound, indicating successful completion of the volume population.

Verify Restored Data :

We are going to exec any pod of sample-restored-sts StatefulSet to verify whether the volume population with the backed up data has been restored successfully.

Now, wait for the StatefulSet pod to go into the Running state.

$ kubectl get pods -n demo 
NAME                    READY   STATUS    RESTARTS   AGE
sample-restored-sts-0   1/1     Running   0          95s
sample-restored-sts-1   1/1     Running   0          65s
sample-restored-sts-2   1/1     Running   0          41s

Verify that the backed up data has been restored into /source/data directory of above pod using the following command,

$ kubectl exec -it -n demo sample-restored-sts-0  -- cat /source/data/data.txt
sample-sts-0

$ kubectl exec -it -n demo sample-restored-sts-1  -- cat /source/data/data.txt
sample-sts-1

$ kubectl exec -it -n demo sample-restored-sts-2  -- cat /source/data/data.txt
sample-sts-2

Cleaning Up

To clean up the Kubernetes resources created by this tutorial, run:

kubectl delete backupconfiguration -n demo sample-backup-sts
kubectl delete backupstorage -n demo gcs-storage
kubectl delete retentionPolicy -n demo demo-retention
kubectl delete secret -n demo gcs-secret
kubectl delete secret -n demo encrypt-secret
kubectl delete statefulset -n demo sample-sts
kubectl delete statefulset -n demo sample-restored-sts
kubectl delete pvc -n demo --all

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