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Stand-alone Volume Backup Overview | Stash
An overview on how stand-alone volume backup works in Stash.
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volume-backup-overview
How does it work?
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guides

Stand-alone Volume Backup Overview

If you are using a volume that can be mounted in multiple workloads, aka ReadWriteMany/RWX, you might want to backup the volume independent of the workloads. Stash supports backup of stand-alone volumes. This guide will give you an overview of how stand-alone volume backup and restore process works in Stash.

How Backup Works

The following diagram shows how Stash takes backup of a stand-alone volume. Open the image in a new tab to see the enlarged version.

  

Stand-alone Volume Backup Overview

Fig: Stand-alone Volume Backup Overview

The backup process consists of the following steps:

  1. At first, a user creates a secret with access credentials of the backend where the backed up data will be stored.

  2. Then, she creates a Repository crd that specifies the backend information along with the secret that holds the credentials to access the backend.

  3. Then, she creates a BackupConfiguration crd targeting the volume. The BackupConfiguration object also specifies the Task to use to backup the volume.

  4. Stash operator watches for BackupConfiguration crd.

  5. Once Stash operator finds a BackupConfiguration crd, it creates a CronJob with the schedule specified in BackupConfiguration object to trigger backup periodically.

  6. On next scheduled slot, the CronJob triggers a backup by creating a BackupSession crd.

  7. Stash operator also watches for BackupSession crd.

  8. When it finds a BackupSession object, it resolves the respective Task and Function and prepares a backup Job definition.

  9. Then, it mounts the targeted volume into the Job and creates it.

  10. The Job takes backup of the targeted volume.

  11. Finally, when backup is completed, the Job sends Prometheus metrics to the Pushgateway running inside Stash operator pod. It also updates the BackupSession and Repository status to reflect the backup procedure.

How Restore Works

The following diagram shows how Stash restores backed up data into a stand-alone volume. Open the image in a new tab to see the enlarged version.

  

Stand-alone Volume Restore Overview

Fig: Stand-alone Volume Restore Overview

The restore process consists of the following steps:

  1. At first, a user creates a RestoreSession crd which specifies the targeted volume where the backed up data will be restored and the Repository crd which holds the backend information where the backed up data has been stored. It also specifies the Task to use to restore the target.

  2. Stash operator watches for RestoreSession object.

  3. Once it finds a RestoreSession object, it resolves the respective Task and Function and prepares a restore Job definition.

  4. Then, it mounts the targeted volume into the Job and creates it.

  5. The Job restores the backed up data into the volume.

  6. Finally, when the restore process is completed, the Job sends Prometheus metrics to the Pushgateway and update the RestoreSession status to reflect restore completion.

Why use Function-Task model to backup or restore a volume

You might be wondering why we have used Function and Task to backup or restore a volume. Well, let us explain.

Function-Task model gives you the flexibility to customize the backup/restore process. For example, it enables you to execute some logic to prepare your apps before backup or execute logic to delete corrupted data before restore. For more details about what are the others benefits of Function-Task model, please visit here.

Next Steps

  • Learn how to backup and restore a stand-alone PVC from here.