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ClickHouse Backup & Restore Overview

KubeDB uses KubeStash to backup and restore databases. KubeStash by AppsCode is a cloud native data backup and recovery solution for Kubernetes workloads and databases. KubeStash utilizes a ClickHouseBackup driver (based on clickhouse-backup) to securely backup ClickHouse databases to any cloud or on-prem storage backend (for example, S3, GCS, Azure Blob storage, Minio, NetApp, Dell EMC etc.).

How Backup Works

The following diagram shows how KubeStash takes backup of a ClickHouse database. Open the image in a new tab to see the enlarged version.

The backup process consists of the following steps:

1. At first, a user creates a Secret. This secret holds the credentials to access the backend where the backed up data will be stored.

2. Then, she creates a BackupStorage custom resource that specifies the backend information, along with the Secret containing the credentials needed to access the backend.

3. KubeStash operator watches for BackupStorage custom resources. When it finds a BackupStorage object, it initializes the BackupStorage by uploading the metadata.yaml file to the specified backend.

4. Next, she creates a BackupConfiguration custom resource that specifies the target ClickHouse database, addon information (including backup tasks), backup schedules, storage backends for storing the backup data, and other additional settings.

5. KubeStash operator watches for BackupConfiguration objects.

6. Once the KubeStash operator finds a BackupConfiguration object, it creates a Repository with the information specified in the BackupConfiguration.

7. KubeStash operator watches for Repository custom resources. When it finds the Repository object, it initializes the Repository by uploading a repository.yaml file into the spec.sessions[*].repositories[*].directory path specified in BackupConfiguration.

8. Then, it creates a CronJob for each session with the schedule specified in BackupConfiguration to trigger backup periodically.

9. KubeStash operator triggers an instant backup as soon as the BackupConfiguration is ready. Backups are otherwise triggered by the CronJob based on the specified schedule.

10. KubeStash operator watches for BackupSession custom resources.

11. When it finds a BackupSession object, it creates a Snapshot custom resource for each Repository specified in the BackupConfiguration.

12. Then it resolves the respective Addon and Function and prepares backup Job definition.

13. Then, it creates the Job to backup the targeted ClickHouse database.

14. The backup Job reads necessary information (e.g. auth secret, port) to connect with the database from the AppBinding CR. It also reads backend information and access credentials from BackupStorage CR, Storage Secret and Repository path respectively.

15. Then, the Job runs clickhouse-backup against the targeted ClickHouse database and uploads the output to the backend.

16. After the backup process is completed, the backup Job updates the status.components[dump] field of the Snapshot resource with backup information of the target ClickHouse database.

How Restore Process Works

The following diagram shows how KubeStash restores backed up data into a ClickHouse database. Open the image in a new tab to see the enlarged version.

The restore process consists of the following steps:

1. At first, a user creates a ClickHouse database where the data will be restored, or the user can use the same ClickHouse database.

2. Then, she creates a RestoreSession custom resource that specifies the target database where the backed-up data will be restored, addon information (including restore tasks), the target snapshot to be restored, the Repository containing that snapshot, and other additional settings.

3. KubeStash operator watches for RestoreSession custom resources.

4. When it finds a RestoreSession custom resource, it resolves the respective Addon and Function and prepares a restore Job definition.

5. Then, it creates the Job to restore the target.

6. The Job reads necessary information to connect with the database from the respective AppBinding CR. It also reads backend information and access credentials from Repository CR and storage Secret respectively.

7. Then, the Job downloads the backed up data from the backend and restores it into the desired ClickHouse database using clickhouse-backup.

8. Finally, when the restore process is completed, the Job updates the status.components[*] field of the RestoreSession with restore information of the target database.

Next Steps

• Backup a ClickHouse database using KubeStash by following the guide from here.