Restoring Volumes for Kubernetes StatefulSets

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 Persistent Volume 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>. Stateful Set 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 pvc 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 pvc naming scheme
    spec:
      accessModes: [ "ReadWriteOnce" ]
      storageClassName: longhorn # must match name from earlier
      resources:
        requests:
          storage: 2Gi # must match size from earlier

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