5

I have a mongodb-replicaset created with the helm chart. The chart creates PVCs based on the StorageClass I provide. I annotate my volumes with a tag picked up by a cron job that snapshots the volumes.

In the event I need to restore from backup snapshots, say in another cluster, I know I can create a volume from the snapshot, but I don't know how to then turn that volume into the PVC that the StatefulSet is expecting and can restart from.

4

I learned that a StatefulSet will look for PVCs with specific names. I figured this out from the documentation at https://kubernetes.io/docs/concepts/workloads/controllers/statefulset/#limitations which says:

The storage for a given Pod must either be provisioned by a PersistentVolume Provisioner based on the requested storage class, or pre-provisioned by an admin.

And through experimentation I discovered that pre-provisioning just meant creating PersistentVolumeClaims with the expected names.

I was able to restore an EBS snapshot to a volume, create a PersistentVolume directly referencing the restored volume id, then create a PersistentVolumeClaim with the correct name. So for instance this mongo installation expects volumes named like datadir-pii-mongodb-replicaset-[0-2] and after restoring the EBS snapshot to a volume I use the following yaml:

apiVersion: v1
kind: PersistentVolume
metadata:
  labels:
    failure-domain.beta.kubernetes.io/region: us-west-2
    failure-domain.beta.kubernetes.io/zone: us-west-2a
  name: pv-a
  namespace: larksettings-pii
spec:
  accessModes:
  - ReadWriteOnce
  capacity:
    storage: 320Gi
  awsElasticBlockStore:
    fsType: xfs
    volumeID: aws://us-west-2a/vol-xxxxxxxxxxxxx
  storageClassName: mongo-xfs

---

apiVersion: v1
kind: PersistentVolumeClaim

metadata:
  labels:
    app: mongodb-replicaset
    release: pii
  name: datadir-pii-mongodb-replicaset-0
  namespace: larksettings-pii
spec:
    accessModes:
    - ReadWriteOnce
    resources:
      requests:
        storage: 320Gi
    storageClassName: mongo-xfs
    volumeName: pv-a

Be careful about availability zones. Since I spanned 3 zones I needed to restore the three snapshots into separate zones and make sure the PersistentVolume spec reflected that.

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0

When you use StatefulSet (or ReplicaSet), it creates Volumes dynamically, because StatufulSet uses PVC template and creates several volumes based on that template. So, you cannot specify which volume will be claimed by PVC. In his case, it is possible to create a PV based on the snapshot, but he can claim just on snapshots. For example, snapshot of replica 1 can be mounted to replica 3. As a matter of fact, it is impossible to recover the installation like that.

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