Appendix A - Backup on volume snapshots ======================================= .. raw:: html .. Note:: Please refer to the official Kubernetes documentation for a list of all the supported `Container Storage Interface (CSI) drivers `_ that provide snapshotting capabilities. 　 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 `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. .. Note:: 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 ` 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@ plugins: - name: barman-cloud.cloudnative-pg.io isWALArchiver: true parameters: barmanObjectName: @OBJECTSTORE_NAME@ As you can see, the ``backup`` section contains both the ``volumeSnapshot`` stanza (controlling physical base backups on volume snapshots) and the ``plugins`` one (controlling the :ref:`WAL archive ` ). .. Note:: Once you have defined the `plugin` , you can decide to use both volume snapshot and plugin 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. Hot and cold backups -------------------- .. 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, making the cluster read-only during this period. For safety, in a cluster already containing fenced instances, a cold snapshot is rejected. 　 By default, CloudNativePG requests an online/hot backup on volume snapshots, using the `PostgreSQL defaults of the low-level API for base backups `_ : - it doesn’t request an immediate checkpoint when starting the backup procedure - it waits for the WAL archiver to archive the last segment of the backup when terminating the backup procedure .. Note:: The default values are suitable for most production environments. Hot backups are consistent and can be used to perform snapshot recovery, as we ensure WAL retention from the start of the backup through a temporary replication slot. However, our recommendation is to rely on cold backups for that purpose. 　 You can explicitly change the default behavior through the following options in the ``.spec.backup.volumeSnapshot`` stanza of the ``Cluster`` resource: - ``online`` : accepting ``true`` (default) or ``false`` as a value - ``onlineConfiguration.immediateCheckpoint`` : whether you want to request an immediate checkpoint before you start the backup procedure or not; technically, it corresponds to the ``fast`` argument you pass to the ``pg_backup_start`` /``pg_start_backup()`` function in PostgreSQL, accepting ``true`` (default) or ``false`` - ``onlineConfiguration.waitForArchive`` : whether you want to wait for the archiver to process the last segment of the backup or not; technically, it corresponds to the ``wait_for_archive`` argument you pass to the ``pg_backup_stop`` /``pg_stop_backup()`` function in PostgreSQL, accepting ``true`` (default) or ``false`` If you want to change the default behavior of your Postgres cluster to take cold backups by default, all you need to do is add the ``online: false`` option to your manifest, as follows: .. code:: yaml # ... backup: volumeSnapshot: online: false # ... If you are instead requesting an immediate checkpoint as the default behavior, you can add this section: .. code:: yaml # ... backup: volumeSnapshot: online: true onlineConfiguration: immediateCheckpoint: true # ... Overriding the default behavior ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ You can change the default behavior defined in the cluster resource by setting different values for ``online`` and, if needed, ``onlineConfiguration`` in the ``Backup`` or ``ScheduledBackup`` objects. For example, in case you want to issue an on-demand cold backup, you can create a ``Backup`` object with ``.spec.online: false`` : .. code:: yaml apiVersion: postgresql.cnpg.io/v1 kind: Backup metadata: name: snapshot-cluster-cold-backup-example spec: cluster: name: snapshot-cluster method: volumeSnapshot online: false Similarly, for the ScheduledBackup: .. code:: yaml apiVersion: postgresql.cnpg.io/v1 kind: ScheduledBackup metadata: name: snapshot-cluster-cold-backup-example spec: schedule: "0 0 0 * * *" backupOwnerReference: self cluster: name: snapshot-cluster method: volumeSnapshot online: false 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 `Kubernetes documentation on Volume Snapshot Classes `_ for details on this standard behavior. Backup Volume Snapshot Deadlines -------------------------------- CloudNativePG supports backups using the volume snapshot method. In some environments, volume snapshots may encounter temporary issues that can be retried. The ``backup.cnpg.io/volumeSnapshotDeadline`` annotation defines how long CloudNativePG should continue retrying recoverable errors before marking the backup as failed. You can add the ``backup.cnpg.io/volumeSnapshotDeadline`` annotation to both ``Backup`` and ``ScheduledBackup`` resources. For ``ScheduledBackup`` resources, this annotation is automatically inherited by any ``Backup`` resources created from the schedule. If not specified, the default retry deadline is **10 minutes**. Error Handling ^^^^^^^^^^^^^^ When a retryable error occurs during a volume snapshot operation: 1. CloudNativePG records the time of the first error. 2. The system retries the operation every **10 seconds**. 3. If the error persists beyond the specified deadline (or the default 10 minutes), the backup is marked as **failed**. Retryable Errors ^^^^^^^^^^^^^^^^ CloudNativePG treats the following types of errors as retryable: - **Server timeout errors** (HTTP 408, 429, 500, 502, 503, 504) - **Conflicts** (optimistic locking errors) - **Internal errors** - **Context deadline exceeded errors** - **Timeout errors from the CSI snapshot controller** Examples ^^^^^^^^ You can add the annotation to a ``ScheduledBackup`` resource as follows: .. code:: yaml apiVersion: postgresql.cnpg.io/v1 kind: ScheduledBackup metadata: name: daily-backup-schedule annotations: backup.cnpg.io/volumeSnapshotDeadline: "20" spec: schedule: "0 0 * * *" backupOwnerReference: self method: volumeSnapshot # other configuration... When you define a ``ScheduledBackup`` with the annotation, any ``Backup`` resources created from this schedule automatically inherit the specified timeout value. In the following example, all backups created from the schedule will have a 30-minute timeout for retrying recoverable snapshot errors. .. code:: yaml apiVersion: postgresql.cnpg.io/v1 kind: ScheduledBackup metadata: name: weekly-backup annotations: backup.cnpg.io/volumeSnapshotDeadline: "30" spec: schedule: "0 0 * * 0" # Weekly backup on Sunday method: volumeSnapshot cluster: name: my-postgresql-cluster Alternatively, you can add the annotation directly to a ``Backup`` Resource: .. code:: yaml apiVersion: postgresql.cnpg.io/v1 kind: Backup metadata: name: my-backup annotations: backup.cnpg.io/volumeSnapshotDeadline: "15" spec: method: volumeSnapshot # other backup configuration... Example of Volume Snapshot Backup --------------------------------- 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. .. Note:: 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 plugins: - name: barman-cloud.cloudnative-pg.io isWALArchiver: true parameters: barmanObjectName: @OBJECTSTORE_NAME@ 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.