Restoring Volumes for Kubernetes Stateful Sets

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

To restore, follow the below instructions based on which plugin you have deployed. The example below uses a Stateful Set with one volume attached to each Pod and two replicas.

CSI Instructions

  1. Connect to the Longhorn UI page in your web browser. Under the Backup tab, select the name of the Stateful Set 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 Stateful Set 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
  1. 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: io.rancher.longhorn # driver must match this
    fsType: ext4
    volumeAttributes:
      numberOfReplicas: <replicas> # must match Longhorn volume value
      staleReplicaTimeout: '30'
    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: io.rancher.longhorn # 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
  1. Go to General Instructions.

Flexvolume Instructions

Because of the implementation of Flexvolume, creating the Longhorn volumes from the Longhorn UI manually can be skipped. Instead, follow these instructions:

  1. Connect to the Longhorn UI page in your web browser. Under the Backup tab, select the name of the Stateful Set volume. Click the dropdown menu of the volume entry and select Get URL.
  • Repeat this step for each volume you need restored. Save these URLs for the next step.
  • If using NFS backups, the URL will appear similar to:
    • nfs://longhorn-nfs-svc.default:/opt/backupstore?backup=backup-c57844b68923408f&volume=pvc-59b20247-99bf-11e8-8a92-be8835d7412a.
  • If using S3 backups, the URL will appear similar to:
    • s3://backupbucket@us-east-1/backupstore?backup=backup-1713a64cd2774c43&volume=longhorn-testvol-g1n1de
  1. Similar to Step 2 for CSI, create a Persistent Volume for each volume you want to restore. storage capacity, storageClassName, and the Flexvolume options must be replaced. This example uses longhorn as the storageClassName.
apiVersion: v1
kind: PersistentVolume
metadata:
  name: statefulset-vol-0
spec:
  capacity:
    storage: <size> # must match "size" parameter below
  accessModes:
    - ReadWriteOnce
  storageClassName: longhorn # must be same name that we will use later
  flexVolume:
    driver: "rancher.io/longhorn" # driver must match this
    fsType: "ext4"
    options:
      size: <size> # must match "storage" parameter above
      numberOfReplicas: <replicas>
      staleReplicaTimeout: <timeout>
      fromBackup: <backup URL> # must be set to Longhorn backup URL
---
apiVersion: v1
kind: PersistentVolume
metadata:
  name: statefulset-vol-1
spec:
  capacity:
    storage: <size> # must match "size" parameter below
  accessModes:
    - ReadWriteOnce
  storageClassName: longhorn # must be same name that we will use later
  flexVolume:
    driver: "rancher.io/longhorn" # driver must match this
    fsType: "ext4"
    options:
      size: <size> # must match "storage" parameter above
      numberOfReplicas: <replicas>
      staleReplicaTimeout: <timeout>
      fromBackup: <backup URL> # must be set to Longhorn backup URL
  1. Go to General Instructions.

General Instructions

Make sure you have followed either the CSI or Flexvolume instructions before following the steps in this section.

  1. In the namespace the Stateful Set 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 Stateful Set>-<index>. Stateful Set Pods are zero-indexed. In this example, the name of the Volume Claim Template is data, the name of the Stateful Set 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
  1. Create the Stateful Set:
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: k8s.gcr.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 Stateful Set Pods.