Restore a Volume for a Kubernetes StatefulSet

Longhorn supports restoring backups, and one of the use cases for this feature is to restore data for use in a Kubernetes StatefulSet, which requires restoring a volume for each replica that was backed up.

To restore, follow the below instructions. The example below uses a StatefulSet with one volume attached to each Pod and two replicas.

  1. Connect to the Longhorn UI page in your web browser. Under the Backup tab, select the name of the StatefulSet volume. Click the dropdown menu of the volume entry and restore it. Name the volume something that can easily be referenced later for the Persistent Volumes.

    • Repeat this step for each volume you need restored.

    • For example, if restoring a StatefulSet with two replicas that had volumes named pvc-01a and pvc-02b, the restore could look like this:

    Backup Name Restored Volume

    pvc-01a

    statefulset-vol-0

    pvc-02b

    statefulset-vol-1

  2. In Kubernetes, create a Persistent Volume for each Longhorn volume that was created. Name the volumes something that can easily be referenced later for the Persistent Volume Claims. storage capacity, numberOfReplicas, storageClassName, and volumeHandle must be replaced below. In the example, we’re referencing statefulset-vol-0 and statefulset-vol-1 in Longhorn and using longhorn as our storageClassName.

     apiVersion: v1
 kind: PersistentVolume
 metadata:
   name: statefulset-vol-0
 spec:
   capacity:
     storage: <size> # must match size of Longhorn volume
   volumeMode: Filesystem
   accessModes:
     - ReadWriteOnce
   persistentVolumeReclaimPolicy: Delete
   csi:
     driver: driver.longhorn.io # driver must match this
     fsType: ext4
     volumeAttributes:
       numberOfReplicas: <replicas> # must match Longhorn volume value
       staleReplicaTimeout: '30' # in minutes
     volumeHandle: statefulset-vol-0 # must match volume name from Longhorn
   storageClassName: longhorn # must be same name that we will use later
 ---
 apiVersion: v1
 kind: PersistentVolume
 metadata:
   name: statefulset-vol-1
 spec:
   capacity:
     storage: <size>  # must match size of Longhorn volume
   volumeMode: Filesystem
   accessModes:
     - ReadWriteOnce
   persistentVolumeReclaimPolicy: Delete
   csi:
     driver: driver.longhorn.io # driver must match this
     fsType: ext4
     volumeAttributes:
       numberOfReplicas: <replicas> # must match Longhorn volume value
       staleReplicaTimeout: '30'
     volumeHandle: statefulset-vol-1 # must match volume name from Longhorn
   storageClassName: longhorn # must be same name that we will use later

  3. In the namespace the StatefulSet will be deployed in, create PersistentVolume Claims for each Persistent Volume. The name of the Persistent Volume Claim must follow this naming scheme:

     <name of Volume Claim Template>-<name of StatefulSet>-<index>

    StatefulSet Pods are zero-indexed. In this example, the name of the Volume Claim Template is data, the name of the StatefulSet is webapp, and there are two replicas, which are indexes 0 and 1.

     apiVersion: v1
 kind: PersistentVolumeClaim
 metadata:
   name: data-webapp-0
 spec:
   accessModes:
   - ReadWriteOnce
   resources:
     requests:
       storage: 2Gi # must match size from earlier
   storageClassName: longhorn # must match name from earlier
   volumeName: statefulset-vol-0 # must reference Persistent Volume
 ---
 apiVersion: v1
 kind: PersistentVolumeClaim
 metadata:
   name: data-webapp-1
 spec:
   accessModes:
   - ReadWriteOnce
   resources:
     requests:
       storage: 2Gi # must match size from earlier
   storageClassName: longhorn # must match name from earlier
   volumeName: statefulset-vol-1 # must reference Persistent Volume

  4. Create the StatefulSet:

     apiVersion: apps/v1beta2
 kind: StatefulSet
 metadata:
   name: webapp # match this with the PersistentVolumeClaim naming scheme
 spec:
   selector:
     matchLabels:
       app: nginx # has to match .spec.template.metadata.labels
   serviceName: "nginx"
   replicas: 2 # by default is 1
   template:
     metadata:
       labels:
         app: nginx # has to match .spec.selector.matchLabels
     spec:
       terminationGracePeriodSeconds: 10
       containers:
       - name: nginx
         image: registry.k8s.io/nginx-slim:0.8
         ports:
         - containerPort: 80
           name: web
         volumeMounts:
         - name: data
           mountPath: /usr/share/nginx/html
   volumeClaimTemplates:
   - metadata:
       name: data # match this with the PersistentVolumeClaim naming scheme
     spec:
       accessModes: [ "ReadWriteOnce" ]
       storageClassName: longhorn # must match name from earlier
       resources:
         requests:
           storage: 2Gi # must match size from earlier

Result: The restored data should now be accessible from inside the StatefulSet Pods.