Backup on volume snapshots ========================== .. Important:: The current implementation of volume snapshots in CloudNativePG supports :ref:`cold backup ` only. Hot backup with direct support of `PostgreSQL's low level API for base backups `_ will be added in version 1.22. Having said this, the current implementation is suitable for production HA environments, as it will by default work on the most aligned standby without impacting the primary. .. Warning:: As noted in the :ref:`backup document ` , a cold snapshot explicitly set to target the primary will result in the primary being fenced for the duration of the backup, rendering the cluster read-only during that time. .. Warning:: A volume snapshot backup requires fencing the target instance. For safety, in a cluster already containing fenced instances, a cold snapshot would be rejected. CloudNativePG is one of the first known cases of database operators that directly leverages the Kubernetes native Volume Snapshot API for both backup and recovery operations, in an entirely declarative way. About standard Volume Snapshots ------------------------------- Volume snapshotting was first introduced in `Kubernetes 1.12 (2018) as alpha `_ , promoted to `beta in 1.17 (2019) `_ , and `moved to GA in 1.20 (2020) `_ . It’s now stable, widely available, and standard, providing 3 custom resource definitions: ``VolumeSnapshot`` , ``VolumeSnapshotContent`` and ``VolumeSnapshotClass`` . This Kubernetes feature defines a generic interface for: - the creation of a new volume snapshot, starting from a PVC - the deletion of an existing snapshot - the creation of a new volume from a snapshot Kubernetes delegates the actual implementation to the underlying CSI drivers (not all of them support volume snapshots). Normally, storage classes that provide volume snapshotting support **incremental and differential block level backup in a transparent way for the application**, which can delegate the complexity and the independent management down the stack, including cross-cluster availability of the snapshots. Requirements ------------ For Volume Snapshots to work with a CloudNativePG cluster, you need to ensure that each storage class used to dynamically provision the PostgreSQL volumes (namely, ``storage`` and ``walStorage`` sections) support volume snapshots. Given that instructions vary from storage class to storage class, please refer to the documentation of the specific storage class and related CSI drivers you have deployed in your Kubernetes system. Normally, it is the :ref:`VolumeSnapshotClass ` that is responsible to ensure that snapshots can be taken from persistent volumes of a given storage class, and managed as ``VolumeSnapshot`` and ``VolumeSnapshotContent`` resources. .. Important:: It is your responsibility to verify with the third party vendor that volume snapshots are supported. CloudNativePG only interacts with the Kubernetes API on this matter and we cannot support issues at the storage level for each specific CSI driver. How to configure Volume Snapshot backups ---------------------------------------- CloudNativePG allows you to configure a given Postgres cluster for Volume Snapshot backups through the ``backup.volumeSnapshot`` stanza. .. Note:: Please refer to :ref:`VolumeSnapshotConfiguration {postgresql-cnpg-io-v1-VolumeSnapshotConfiguration} ` in the API reference for a full list of options. A generic example with volume snapshots (assuming that PGDATA and WALs share the same storage class) is the following: .. code:: yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: snapshot-cluster spec: instances: 3 storage: storageClass: @STORAGE_CLASS@ size: 10Gi walStorage: storageClass: @STORAGE_CLASS@ size: 10Gi backup: # Volume snapshot backups volumeSnapshot: className: @VOLUME_SNAPSHOT_CLASS_NAME@ # WAL archive barmanObjectStore: # ... As you can see, the ``backup`` section contains both the ``volumeSnapshot`` stanza (controlling physical base backups on volume snapshots) and the ``barmanObjectStore`` one (controlling the :ref:`WAL archive ` ). .. Note:: Once you have defined the `barmanObjectStore` , you can decide to use both volume snapshot and object store backup strategies simultaneously to take physical backups. The ``volumeSnapshot.className`` option allows you to reference the default ``VolumeSnapshotClass`` object used for all the storage volumes you have defined in your PostgreSQL cluster. .. Note:: In case you are using a different storage class for `PGDATA` and WAL files, you can specify a separate `VolumeSnapshotClass` for that volume through the `walClassName` option (which defaults to the same value as `className` ). Once a cluster is defined for volume snapshot backups, you need to define a ``ScheduledBackup`` resource that requests such backups on a periodic basis. Persistence of volume snapshot objects -------------------------------------- By default, ``VolumeSnapshot`` objects created by CloudNativePG are retained after deleting the ``Backup`` object that originated them, or the ``Cluster`` they refer to. Such behavior is controlled by the ``.spec.backup.volumeSnapshot.snapshotOwnerReference`` option which accepts the following values: - ``none`` : no ownership is set, meaning that ``VolumeSnapshot`` objects persist after the ``Backup`` and/or the ``Cluster`` resources are removed - ``backup`` : the ``VolumeSnapshot`` object is owned by the ``Backup`` resource that originated it, and when the backup object is removed, the volume snapshot is also removed - ``cluster`` : the ``VolumeSnapshot`` object is owned by the ``Cluster`` resource that is backed up, and when the Postgres cluster is removed, the volume snapshot is also removed In case a ``VolumeSnapshot`` is deleted, the ``deletionPolicy`` specified in the ``VolumeSnapshotContent`` is evaluated: - if set to ``Retain`` , the ``VolumeSnapshotContent`` object is kept - if set to ``Delete`` , the ``VolumeSnapshotContent`` object is removed as well .. Warning:: `VolumeSnapshotContent` objects do not keep all the information regarding the backup and the cluster they refer to (like the annotations and labels that are contained in the `VolumeSnapshot` object). Although possible, restoring from just this kind of object might not be straightforward. For this reason, our recommendation is to always backup the `VolumeSnapshot` definitions, even using a Kubernetes level data protection solution. The value in ``VolumeSnapshotContent`` is determined by the ``deletionPolicy`` set in the corresponding ``VolumeSnapshotClass`` definition, which is referenced in the ``.spec.backup.volumeSnapshot.className`` option. Please refer to the :ref:`Kubernetes documentation on Volume Snapshot Classes ` for details on this standard behavior. Example ------- The following example shows how to configure volume snapshot base backups on an EKS cluster on AWS using the ``ebs-sc`` storage class and the ``csi-aws-vsc`` volume snapshot class. .. Important:: If you are interested in testing the example, please read `Volume Snapshots `_ for detailed instructions on the installation process for the storage class and the snapshot class. The following manifest creates a ``Cluster`` that is ready to be used for volume snapshots and that stores the WAL archive in a S3 bucket via IAM role for the Service Account (IRSA, see :ref:`AWS S3 ` ): .. code:: yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: hendrix spec: instances: 3 storage: storageClass: ebs-sc size: 10Gi walStorage: storageClass: ebs-sc size: 10Gi backup: volumeSnapshot: className: csi-aws-vsc barmanObjectStore: destinationPath: s3://@BUCKET_NAME@/ s3Credentials: inheritFromIAMRole: true wal: compression: gzip maxParallel: 2 serviceAccountTemplate: metadata: annotations: eks.amazonaws.com/role-arn: "@ARN@" - -- apiVersion: postgresql.cnpg.io/v1 kind: ScheduledBackup metadata: name: hendrix-vs-backup spec: cluster: name: hendrix method: volumeSnapshot schedule: 0 0 0 * * * backupOwnerReference: cluster immediate: true The last resource defines daily volume snapshot backups at midnight, requesting one immediately after the cluster is created.