Project: EDB (App Definition and Development / Database)
File: recovery.md

In PostgreSQL terminology, recovery is the process of starting a PostgreSQL instance using an existing backup. The PostgreSQL recovery mechanism is very solid and rich. It also supports point-in-time recovery (PITR), which allows you to restore a given cluster up to any point in time, from the first available backup in your catalog to the last archived WAL. (The WAL archive is mandatory in this case.) In CloudNativePG, you can't perform recovery in place on an existing cluster. Recovery is instead a way to bootstrap a new Postgres cluster starting from an available physical backup. !!! Note For details on the `bootstrap` stanza, see . The `recovery` bootstrap mode lets you create a cluster from an existing physical base backup. You then reapply the WAL files containing the REDO log from the archive. WAL files are pulled from the defined recovery object store. Base backups can be taken either on object stores or using volume snapshots (from version 1.21). !!! Warning Recovery using volume snapshots had an initial release on 1.20.1. Because of the amount of progress on the feature for 1.21.0, to use volume snapshots, we strongly advise you to upgrade to 1.21 or more advanced releases. You can achieve recovery from a recovery object store in two ways: We recommend using a recovery object store, that is, a backup of another cluster created by Barman Cloud and defined by way of the `barmanObjectStore` option in the `externalClusters` section. Alternatively, you can use an existing `Backup` object in the same namespace. Both recovery methods enable either full recovery (up to the last available WAL) or up to a . When performing a full recovery, you can also start the cluster in replica mode (see for reference). !!! Important If using replica mode, make sure that the PostgreSQL configuration (`.spec.postgresql.parameters`) of the recovered cluster is compatible with the original one from a physical replication standpoint. For recovery using volume snapshots: Use a consistent set of `VolumeSnapshot` objects that all belong to the same backup and are identified by the same `cnpg.io/cluster` and `cnpg.io/backupName` labels. Then, recover through the `volumeSnapshots` option in the `.spec.bootstrap.recovery` stanza, as described in . You can recover from a backup created by Barman Cloud and stored on a supported object store. After you define the external cluster, including all the required configuration in the `barmanObjectStore` section, you need to reference it in the `.spec.recovery.source` option. This example defines a recovery object store in a blob container in Azure: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-restore spec: [...] superuserSecret: name: superuser-secret bootstrap: recovery: source: clusterBackup externalClusters: name: clusterBackup barmanObjectStore: destinationPath: https://STORAGEACCOUNTNAME.blob.core.windows.net/CONTAINERNAME/ azureCredentials: storageAccount: name: recovery-object-store-secret key: storageaccountname storageKey: name: recovery-object-store-secret key: storageaccountkey wal: maxParallel: 8 ``` !!! Important By default, the `recovery` method strictly uses the `name` of the cluster in the `externalClusters` section as the name of the main folder of the backup data within the object store. This name is normally reserved for the name of the server. You can specify a different folder name using the `barmanObjectStore.serverName` property. !!! Note This example takes advantage of the parallel WAL restore feature, dedicating up to 8 jobs to concurrently fetch the required WAL files from the

This feature can appreciably reduce the recovery time. Make sure that you plan ahead for this scenario and correctly tune the value of this parameter for your environment. It will make a difference when you need it, and you will. !!! Warning When creating replicas after recovering the primary instance from the volume snapshot, the operator might end up using `pg_basebackup` to synchronize them. This behavior results in a slower process, depending on the size of the database. This limitation will be lifted in the future when support for online backups and PVC cloning are introduced. CloudNativePG can create a new cluster from a `VolumeSnapshot` of a PVC of an existing `Cluster` that's been taken using the declarative API for [volume snapshot backups](backup_volumesnapshot.md). You must specify the name of the snapshot, as in the following example: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-restore spec: [...] bootstrap: recovery: volumeSnapshots: storage: name: <snapshot name> kind: VolumeSnapshot apiGroup: snapshot.storage.k8s.io ``` In case the backed-up cluster was using a separate PVC to store the WAL files, the recovery must include that too: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-restore spec: [...] bootstrap: recovery: volumeSnapshots: storage: name: <snapshot name> kind: VolumeSnapshot apiGroup: snapshot.storage.k8s.io walStorage: name: <snapshot name> kind: VolumeSnapshot apiGroup: snapshot.storage.k8s.io ``` !!! Warning If bootstrapping a replica-mode cluster from snapshots, to leverage snapshots for the standby instances and not just the primary, we recommend that you: Start with a single instance replica cluster. The primary instance will be recovered using the snapshot, and available WALs from the source cluster. Take a snapshot of the primary in the replica cluster. Increase the number of instances in the replica cluster as desired. If a `Backup` resource is already available in the namespace in which you need to create the cluster, you can specify the name using `.spec.bootstrap.recovery.backup.name`, as in the following example: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-example-initdb spec: instances: 3 bootstrap: recovery: backup: name: backup-example storage: size: 1Gi ``` This bootstrap method allows you to specify just a reference to the backup that needs to be restored. The previous example implies the application database and its owning user is the default one, `app`. If the PostgreSQL cluster being restored was using different names, you can specify them as documented in [Configure the application database](#configure-the-application-database). Whether you recover from a recovery object store, a volume snapshot, or an existing `Backup` resource, the following considerations apply: The application database name and the application database user are preserved from the backup that's being restored. The operator doesn't currently attempt to back up the underlying secrets, as this is part of the usual maintenance activity of the Kubernetes cluster. To preserve the original postgres user password, you need to properly configure `enableSuperuserAccess` and supply a `superuserSecret`. By default, the recovery continues up to the latest available WAL on the default target timeline (`latest`). You can optionally specify a `recoveryTarget` to perform a point-in-time recovery (see ). !!! Important Consider using the `barmanObjectStore.wal.maxParallel` option to speed up WAL fetching from the archive by concurrently downloading the transaction logs from the recovery object

Instead of replaying all the WALs up to the latest one, after extracting a base backup, you can ask PostgreSQL to stop replaying WALs at any given point in time. PostgreSQL uses this technique to achieve PITR. The presence of a WAL archive is mandatory. !!! Important PITR requires you to specify a recovery target by using the options described in . The operator generates the configuration parameters required for this feature to work if you specify a recovery target. This example uses a recovery object store in Azure that contains both the base backups and the WAL archive. The recovery target is based on a requested timestamp. ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-restore-pitr spec: instances: 3 storage: size: 5Gi bootstrap: recovery: source: clusterBackup recoveryTarget: targetTime: "2023-08-11 11:14:21.00000+02" externalClusters: name: clusterBackup barmanObjectStore: destinationPath: https://STORAGEACCOUNTNAME.blob.core.windows.net/CONTAINERNAME/ azureCredentials: storageAccount: name: recovery-object-store-secret key: storageaccountname storageKey: name: recovery-object-store-secret key: storageaccountkey wal: maxParallel: 8 ``` In this example, you had to specify only the `targetTime` in the form of a timestamp. You didn't have to specify the base backup from which to start the recovery. The `backupID` option is the one that allows you to specify the base backup from which to initiate the recovery process. By default, this value is empty. If you assign a value to it (in the form of a Barman backup ID), the operator uses that backup as the base for the recovery. !!! Important You need to make sure that such a backup exists and is accessible. If you don't specify the backup ID, the operator detects the base backup for the recovery as follows: When you use `targetTime` or `targetLSN`, the operator selects the closest backup that was completed before that target. Otherwise, the operator selects the last available backup, in chronological order. The example that follows uses: A Kubernetes volume snapshot for the `PGDATA` containing the base backup from which to start the recovery process. This snapshot is identified in the `recovery.volumeSnapshots` section and called `test-snapshot-1`. A recovery object store in MinIO containing the WAL archive. The object store is identified by the `recovery.source` option in the form of an external cluster definition. The recovery target is based on a requested timestamp. ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-example-snapshot spec: bootstrap: recovery: source: cluster-example-with-backup volumeSnapshots: storage: name: test-snapshot-1 kind: VolumeSnapshot apiGroup: snapshot.storage.k8s.io recoveryTarget: targetTime: "2023-07-06T08:00:39" externalClusters: name: cluster-example-with-backup barmanObjectStore: destinationPath: s3://backups/ endpointURL: http://minio:9000 s3Credentials: accessKeyId: name: minio key: ACCESSKEYID secretAccessKey: name: minio key: ACCESSSECRETKEY ``` !!! Note If the backed-up cluster had `walStorage` enabled, you also must specify the volume snapshot containing the `PGWAL` directory, as mentioned in . !!! Warning It's your responsibility to ensure that the end time of the base backup in the volume snapshot is before the recovery target timestamp. Here are the recovery target criteria you can use: targetTime : Time stamp up to which recovery proceeds, expressed in format. (The precise stopping point is also influenced by the `exclusive` option.) targetXID : Transaction ID up to which recovery proceeds. (The precise stopping point is also influenced by the `exclusive` option.) Keep in mind that while transaction IDs are assigned sequentially at transaction start, transactions can complete in a different numeric order. The transactions that are recovered are those that committed before (and optionally including) the specified

targetName : Named restore point (created with `pgcreaterestore_point()`) to which recovery proceeds. targetLSN : LSN of the write-ahead log location up to which recovery proceeds. (The precise stopping point is also influenced by the `exclusive` option.) targetImmediate : Recovery ends as soon as a consistent state is reached, that is, as early as possible. When restoring from an online backup, this means the point where taking the backup ended. !!! Important The operator can retrieve the closest backup when you specify either `targetTime` or `targetLSN`. However, this isn't possible for the remaining targets: `targetName`, `targetXID`, and `targetImmediate`. In such cases, it's important to specify `backupID`, unless the last available backup in the catalog is acceptable. This example uses a `targetName`-based recovery target: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster [...] bootstrap: recovery: source: clusterBackup recoveryTarget: backupID: 20220616T142236 targetName: 'restorepoint1' [...] ``` You can choose only a single one among the targets in each `recoveryTarget` configuration. Additionally, you can specify `targetTLI` to force recovery to a specific timeline. By default, the previous parameters are considered to be inclusive, stopping just after the recovery target, matching . You can request exclusive behavior, stopping right before the recovery target, by setting the `exclusive` parameter to `true`. The following example shows this behavior, relying on a blob container in Azure for both base backups and the WAL archive: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-restore-pitr spec: instances: 3 storage: size: 5Gi bootstrap: recovery: source: clusterBackup recoveryTarget: backupID: 20220616T142236 targetName: "maintenance-activity" exclusive: true externalClusters: name: clusterBackup barmanObjectStore: destinationPath: https://STORAGEACCOUNTNAME.blob.core.windows.net/CONTAINERNAME/ azureCredentials: storageAccount: name: recovery-object-store-secret key: storageaccountname storageKey: name: recovery-object-store-secret key: storageaccountkey wal: maxParallel: 8 ``` For the recovered cluster, you can configure the application database name and credentials with additional configuration. To update application database credentials, you can generate your own passwords, store them as secrets, and update the database to use the secrets. Or you can also let the operator generate a secret with a randomly secure password for use. See for more information about secrets. This example configures the application database `app` with owner `app` and supplied secret `app-secret`. ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster [...] spec: bootstrap: recovery: database: app owner: app secret: name: app-secret [...] ``` With this configuration, the following happens after recovery is complete: If database `app` doesn't exist, a new database `app` is created. If user `app` doesn't exist, a new user `app` is created. if user `app` isn't the owner of the database, user `app` is granted as owner of database `app`. If the value of `username` matches the value of `owner` in the secret, the password of application database is changed to the value of `password` in the secret. !!! Important For a replica cluster with replica mode enabled, the operator doesn't create any database or user in the PostgreSQL instance. These are recovered from the original cluster. <!-- TODO: do we need this section? --> <!-- Also, "under the hood" is an idiom and should be replaced with something more precise --> You can use the data uploaded to the object storage to bootstrap a new cluster from an existing

The operator orchestrates the recovery process using the `barman-cloud-restore` tool (for the base backup) and the `barman-cloud-wal-restore` tool (for WAL files, including parallel support, if requested). For details and instructions on the `recovery` bootstrap method, see . !!! Important If you're not familiar with how works, we suggest that you configure the recovery cluster as the original one when it comes to `.spec.postgresql.parameters`. Once the new cluster is restored, you can then change the settings as desired. The way it works is that the operator injects an init container in the first instance of the new cluster, and the init container starts recovering the backup from the object storage. !!! Important The duration of the base backup copy in the new PVC depends on the size of the backup, as well as the speed of both the network and the storage. When the base backup recovery process is complete, the operator starts the Postgres instance in recovery mode. In this phase, PostgreSQL is up, though not able to accept connections, and the pod is healthy according to the liveness probe. By way of the `restore_command`, PostgreSQL starts fetching WAL files from the archive. (You can speed up this phase by setting the `maxParallel` option and enabling the parallel WAL restore capability.) This phase terminates when PostgreSQL reaches the target (either the end of the WAL or the required target in case of PITR. You can optionally specify a `recoveryTarget` to perform a PITR. If left unspecified, the recovery continues up to the latest available WAL on the default target timeline (`latest`). Once the recovery is complete, the operator sets the required superuser password into the instance. The new primary instance starts as usual, and the remaining instances join the cluster as replicas. The process is transparent for the user and is managed by the instance manager running in the pods. <!-- TODO: do we need this section? --> A manifest for a cluster restore might include a `backup` section. This means that,after recovery, the new cluster starts archiving WALs and taking backups if configured to do so. For example, this section is part of a manifest for a cluster bootstrapping from the cluster `cluster-example-backup`. In the storage bucket, it creates a folder named `recoveredCluster`, where the base backups and WALs of the recovered cluster are stored. ``` yaml backup: barmanObjectStore: destinationPath: s3://backups/ endpointURL: http://minio:9000 serverName: "recoveredCluster" s3Credentials: accessKeyId: name: minio key: ACCESSKEYID secretAccessKey: name: minio key: ACCESSSECRETKEY retentionPolicy: "30d" externalClusters: name: cluster-example-backup barmanObjectStore: destinationPath: s3://backups/ endpointURL: http://minio:9000 s3Credentials: ``` Don't reuse the same `barmanObjectStore` configuration for different clusters. There might be cases where the existing information in the storage buckets could be overwritten by the new cluster. !!! Warning The operator includes a safety check to ensure a cluster doesn't overwrite a storage bucket that contained information. A cluster that would overwrite existing storage remains in the state `Setting up primary` with pods in an error state. The pod logs show: `ERROR: WAL archive check failed for server recoveredCluster: Expected empty archive`. !!! Important If you set the `cnpg.io/skipEmptyWalArchiveCheck` annotation to `enabled` in the recovered cluster, you can skip the safety check. We don't recommend skipping the check because, for the general use case, the check works fine. Skip this check only if you're familiar with the PostgreSQL recovery system, as severe data loss can occur.