Project: CloudNativePG (App Definition and Development / Database)
File: bootstrap.md

This section describes the options you have to create a new PostgreSQL cluster and the design rationale behind them. There are primarily two ways to bootstrap a new cluster: from scratch (`initdb`) from an existing PostgreSQL cluster, either directly (`pg_basebackup`) or indirectly through a physical base backup (`recovery`) The `initdb` bootstrap also offers the possibility to import one or more databases from an existing Postgres cluster, even outside Kubernetes, and having a different major version of Postgres. For more detailed information about this feature, please refer to the section. !!! Important Bootstrapping from an existing cluster opens up the possibility to create a replica cluster, that is an independent PostgreSQL cluster which is in continuous recovery, synchronized with the source and that accepts read-only connections. !!! Warning CloudNativePG requires both the `postgres` user and database to always exists. Using the local Unix Domain Socket, it needs to connect as `postgres` user to the `postgres` database via `peer` authentication in order to perform administrative tasks on the cluster. DO NOT DELETE the `postgres` user or the `postgres` database!!! !!! Info CloudNativePG is gradually introducing support for for both incremental and differential copy in backup and recovery operations - if supported by the underlying storage classes. Please see for details. The bootstrap method can be defined in the `bootstrap` section of the cluster specification. CloudNativePG currently supports the following bootstrap methods: `initdb`: initialize a new PostgreSQL cluster (default) `recovery`: create a PostgreSQL cluster by restoring from a base backup of an existing cluster and, if needed, replaying all the available WAL files or up to a given point in time `pg_basebackup`: create a PostgreSQL cluster by cloning an existing one of the same major version using `pg_basebackup` via streaming replication protocol - useful if you want to migrate databases to CloudNativePG, even from outside Kubernetes. Differently from the `initdb` method, both `recovery` and `pg_basebackup` create a new cluster based on another one (either offline or online) and can be used to spin up replica clusters. They both rely on the definition of external clusters. Given that there are several possible backup methods and combinations of backup storage that the CloudNativePG operator provides, please refer to the for guidance on each method. !!! Seealso "API reference" Please refer to the for more information. The `externalClusters` section provides a mechanism for specifying one or more PostgreSQL clusters associated with the current configuration. Its primary use cases include: Importing Databases: Specify an external source to be utilized during the via logical backup and restore, as part of the `initdb` bootstrap method. Cross-Region Replication: Define a cross-region PostgreSQL cluster employing physical replication, capable of extending across distinct Kubernetes clusters or traditional VM/bare-metal environments. Recovery from Physical Base Backup: Recover, fully or at a given Point-In-Time, a PostgreSQL cluster by referencing a physical base backup. !!! Info Ongoing development will extend the functionality of `externalClusters` to accommodate additional use cases, such as logical replication and foreign servers in future releases. As far as bootstrapping is concerned, `externalClusters` can be used to define the source PostgreSQL cluster for either the `pg_basebackup` method or the `recovery`

An external cluster needs to have: a name that identifies the origin cluster, to be used as a reference via the `source` option at least one of the following: information about streaming connection information about the recovery object store, which is a Barman Cloud compatible object store that contains: the WAL archive (required for Point In Time Recovery) the catalog of physical base backups for the Postgres cluster !!! Note A recovery object store is normally an AWS S3, or an Azure Blob Storage, or a Google Cloud Storage source that is managed by Barman Cloud. When only the streaming connection is defined, the source can be used for the `pg_basebackup` method. When only the recovery object store is defined, the source can be used for the `recovery` method. When both are defined, any of the two bootstrap methods can be chosen. Furthermore, in case of `pg_basebackup` or full `recovery` point in time, the cluster is eligible for replica cluster mode. This means that the cluster is continuously fed from the source, either via streaming, via WAL shipping through the PostgreSQL's `restore_command`, or any of the two. !!! Seealso "API reference" Please refer to the for more information. Whenever a password is supplied within an `externalClusters` entry, CloudNativePG autonomously manages a for it, residing at `/controller/external/NAME/pgpass` in each instance. This approach empowers CloudNativePG to securely establish connections with an external server without exposing any passwords in the connection string. Instead, the connection safely references the aforementioned file through the `passfile` connection parameter. The `initdb` bootstrap method is used to create a new PostgreSQL cluster from scratch. It is the default one unless specified differently. The following example contains the full structure of the `initdb` configuration: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-example-initdb spec: instances: 3 bootstrap: initdb: database: app owner: app secret: name: app-secret storage: size: 1Gi ``` The above example of bootstrap will: create a new `PGDATA` folder using PostgreSQL's native `initdb` command create an unprivileged user named `app` set the password of the latter (`app`) using the one in the `app-secret` secret (make sure that `username` matches the same name of the `owner`) create a database called `app` owned by the `app` user. Thanks to the convention over configuration paradigm, you can let the operator choose a default database name (`app`) and a default application user name (same as the database name), as well as randomly generate a secure password for both the superuser and the application user in PostgreSQL. Alternatively, you can generate your password, store it as a secret, and use it in the PostgreSQL cluster - as described in the above example. The supplied secret must comply with the specifications of the . As a result, the `username` in the secret must match the one of the `owner` (for the application secret) and `postgres` for the superuser one. The following is an example of a `basic-auth` secret: ```yaml apiVersion: v1 data: username: YXBw password: cGFzc3dvcmQ= kind: Secret metadata: name: app-secret type: kubernetes.io/basic-auth ``` The application database is the one that should be used to store application data. Applications should connect to the cluster with the user that owns the application database. !!! Important If you need to create additional users, please refer to

In case you don't supply any database name, the operator will proceed by convention and create the `app` database, and adds it to the cluster definition using a defaulting webhook. The user that owns the database defaults to the database name instead. The application user is not used internally by the operator, which instead relies on the superuser to reconcile the cluster with the desired status. The actual PostgreSQL data directory is created via an invocation of the `initdb` PostgreSQL command. If you need to add custom options to that command (i.e., to change the `locale` used for the template databases or to add data checksums), you can use the following parameters: dataChecksums : When `dataChecksums` is set to `true`, CNPG invokes the `-k` option in `initdb` to enable checksums on data pages and help detect corruption by the I/O system - that would otherwise be silent (default: `false`). encoding : When `encoding` set to a value, CNPG passes it to the `--encoding` option in `initdb`, which selects the encoding of the template database (default: `UTF8`). localeCollate : When `localeCollate` is set to a value, CNPG passes it to the `--lc-collate` option in `initdb`. This option controls the collation order (`LC_COLLATE` subcategory), as defined in from the PostgreSQL documentation (default: `C`). localeCType : When `localeCType` is set to a value, CNPG passes it to the `--lc-ctype` option in `initdb`. This option controls the collation order (`LC_CTYPE` subcategory), as defined in from the PostgreSQL documentation (default: `C`). walSegmentSize : When `walSegmentSize` is set to a value, CNPG passes it to the `--wal-segsize` option in `initdb` (default: not set - defined by PostgreSQL as 16 megabytes). !!! Note The only two locale options that CloudNativePG implements during the `initdb` bootstrap refer to the `LCCOLLATE` and `LCTYPE` subcategories. The remaining locale subcategories can be configured directly in the PostgreSQL configuration, using the `lcmessages`, `lcmonetary`, `lc_numeric`, and `lc_time` parameters. The following example enables data checksums and sets the default encoding to `LATIN1`: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-example-initdb spec: instances: 3 bootstrap: initdb: database: app owner: app dataChecksums: true encoding: 'LATIN1' storage: size: 1Gi ``` !!! Warning CloudNativePG supports another way to customize the behavior of the `initdb` invocation, using the `options` subsection. However, given that there are options that can break the behavior of the operator (such as `--auth` or `-d`), this technique is deprecated and will be removed from future versions of the API. You can also specify a custom list of queries that will be executed once, just after the database is created and configured. These queries will be executed as the superuser (`postgres`), connected to the `postgres` database: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-example-initdb spec: instances: 3 bootstrap: initdb: database: app owner: app dataChecksums: true localeCollate: 'en_US' localeCType: 'en_US' postInitSQL: CREATE DATABASE angus storage: size: 1Gi ``` !!! Warning Please use the `postInitSQL`, `postInitApplicationSQL` and `postInitTemplateSQL` options with extreme care, as queries are run as a superuser and can disrupt the entire cluster. An error in any of those queries interrupts the bootstrap phase, leaving the cluster

Moreover, you can specify a list of Secrets and/or ConfigMaps which contains SQL script that will be executed after the database is created and configured. These SQL script will be executed using the superuser role (`postgres`), connected to the database specified in the `initdb` section: ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-example-initdb spec: instances: 3 bootstrap: initdb: database: app owner: app postInitApplicationSQLRefs: secretRefs: name: my-secret key: secret.sql configMapRefs: name: my-configmap key: configmap.sql storage: size: 1Gi ``` !!! Note The SQL scripts referenced in `secretRefs` will be executed before the ones referenced in `configMapRefs`. For both sections the SQL scripts will be executed respecting the order in the list. Inside SQL scripts, each SQL statement is executed in a single exec on the server according to the , comments can be included, but internal command like `psql` cannot. !!! Warning Please make sure the existence of the entries inside the ConfigMaps or Secrets specified in `postInitApplicationSQLRefs`, otherwise the bootstrap will fail. Errors in any of those SQL files will prevent the bootstrap phase to complete successfully. CloudNativePG enables the bootstrap of a cluster starting from another one of the same major version. This operation can happen by connecting directly to the source cluster via streaming replication (`pg_basebackup`), or indirectly via an existing physical base backup (`recovery`). The source cluster must be defined in the `externalClusters` section, identified by `name` (our recommendation is to use the same `name` of the origin cluster). !!! Important By default the `recovery` method strictly uses the `name` of the cluster in the `externalClusters` section to locate the main folder of the backup data within the object store, which is normally reserved for the name of the server. You can specify a different one with the `barmanObjectStore.serverName` property (by default assigned to the value of `name` in the external cluster definition). Given the several possibilities, methods, and combinations that the CloudNativePG operator provides in terms of backup and recovery, please refer to the . The `pg_basebackup` bootstrap mode lets you create a new cluster (target) as an exact physical copy of an existing and binary compatible PostgreSQL instance (source), through a valid streaming replication connection. The source instance can be either a primary or a standby PostgreSQL server. The primary use case for this method is represented by migrations to CloudNativePG, either from outside Kubernetes or within Kubernetes (e.g., from another operator). !!! Warning The current implementation creates a snapshot of the origin PostgreSQL instance when the cloning process terminates and immediately starts the created cluster. See below for details. Similar to the case of the `recovery` bootstrap method, once the clone operation completes, the operator will take ownership of the target cluster, starting from the first instance. This includes overriding some configuration parameters, as required by CloudNativePG, resetting the superuser password, creating the `streaming_replica` user, managing the replicas, and so on. The resulting cluster will be completely independent of the source instance. !!! Important Configuring the network between the target instance and the source instance goes beyond the scope of CloudNativePG documentation, as it depends on the actual context and

The streaming replication client on the target instance, which will be transparently managed by `pg_basebackup`, can authenticate itself on the source instance in any of the following ways: via via The latter is the recommended one if you connect to a source managed by CloudNativePG or configured for TLS authentication. The first option is, however, the most common form of authentication to a PostgreSQL server in general, and might be the easiest way if the source instance is on a traditional environment outside Kubernetes. Both cases are explained below. The following requirements apply to the `pg_basebackup` bootstrap method: target and source must have the same hardware architecture target and source must have the same major PostgreSQL version target and source must have the same tablespaces source must be configured with enough `maxwalsenders` to grant access from the target for this one-off operation by providing at least one walsender for the backup plus one for WAL streaming the network between source and target must be configured to enable the target instance to connect to the PostgreSQL port on the source instance source must have a role with `REPLICATION LOGIN` privileges and must accept connections from the target instance for this role in `pg_hba.conf`, preferably via TLS (see below) target must be able to successfully connect to the source PostgreSQL instance using a role with `REPLICATION LOGIN` privileges !!! Seealso For further information, please refer to the , the and the in the PostgreSQL documentation. As explained in the requirements section, you need to have a user with either the `SUPERUSER` or, preferably, just the `REPLICATION` privilege in the source instance. If the source database is created with CloudNativePG, you can reuse the `streaming_replica` user and take advantage of client TLS certificates authentication (which, by default, is the only allowed connection method for `streaming_replica`). For all other cases, including outside Kubernetes, please verify that you already have a user with the `REPLICATION` privilege, or create a new one by following the instructions below. As `postgres` user on the source system, please run: ```console createuser -P --replication streaming_replica ``` Enter the password at the prompt and save it for later, as you will need to add it to a secret in the target instance. !!! Note Although the name is not important, we will use `streaming_replica` for the sake of simplicity. Feel free to change it as you like, provided you adapt the instructions in the following sections. The first authentication method supported by CloudNativePG with the `pg_basebackup` bootstrap is based on username and password matching. Make sure you have the following information before you start the procedure: location of the source instance, identified by a hostname or an IP address and a TCP port replication username (`streaming_replica` for simplicity) password You might need to add a line similar to the following to the `pg_hba.conf` file on the source PostgreSQL instance: ``` host replication streaming_replica all md5 ``` The following manifest creates a new PostgreSQL 16.3 cluster, called `target-db`, using the `pg_basebackup` bootstrap method to clone an external PostgreSQL cluster defined as `source-db` (in the `externalClusters` array). As you can see, the `source-db` definition points to the `source-db.foo.com` host and connects as the `streaming_replica` user, whose password is stored in the `password` key of the `source-db-replica-user` secret. ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: target-db spec: instances: 3 imageName:

bootstrap: pg_basebackup: source: source-db storage: size: 1Gi externalClusters: name: source-db connectionParameters: host: source-db.foo.com user: streaming_replica password: name: source-db-replica-user key: password ``` All the requirements must be met for the clone operation to work, including the same PostgreSQL version (in our case 16.3). The second authentication method supported by CloudNativePG with the `pg_basebackup` bootstrap is based on TLS client certificates. This is the recommended approach from a security standpoint. The following example clones an existing PostgreSQL cluster (`cluster-example`) in the same Kubernetes cluster. !!! Note This example can be easily adapted to cover an instance that resides outside the Kubernetes cluster. The manifest defines a new PostgreSQL 16.3 cluster called `cluster-clone-tls`, which is bootstrapped using the `pg_basebackup` method from the `cluster-example` external cluster. The host is identified by the read/write service in the same cluster, while the `streaming_replica` user is authenticated thanks to the provided keys, certificate, and certification authority information (respectively in the `cluster-example-replication` and `cluster-example-ca` secrets). ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster metadata: name: cluster-clone-tls spec: instances: 3 imageName: ghcr.io/cloudnative-pg/postgresql:16.3 bootstrap: pg_basebackup: source: cluster-example storage: size: 1Gi externalClusters: name: cluster-example connectionParameters: host: cluster-example-rw.default.svc user: streaming_replica sslmode: verify-full sslKey: name: cluster-example-replication key: tls.key sslCert: name: cluster-example-replication key: tls.crt sslRootCert: name: cluster-example-ca key: ca.crt ``` We also support to configure the application database for cluster which bootstrap from a live cluster, just like the case of `initdb` and `recovery` bootstrap method. If the new cluster is created as a replica cluster (with replica mode enabled), application database configuration will be skipped. The following example configure the application database `app` with password in supplied secret `app-secret` after bootstrap from a live cluster. ```yaml apiVersion: postgresql.cnpg.io/v1 kind: Cluster [...] spec: bootstrap: pg_basebackup: database: app owner: app secret: name: app-secret source: cluster-example ``` With the above configuration, the following will happen after recovery is completed: if database `app` does not exist, a new database `app` will be created. if user `app` does not exist, a new user `app` will be created. if user `app` is not the owner of database, user `app` will be granted as owner of database `app`. If value of `username` match value of `owner` in secret, the password of application database will be changed to the value of `password` in secret. !!! Important For a replica cluster with replica mode enabled, the operator will not create any database or user in the PostgreSQL instance, as these will be recovered from the original cluster. The `pg_basebackup` method takes a snapshot of the source instance in the form of a PostgreSQL base backup. All transactions written from the start of the backup to the correct termination of the backup will be streamed to the target instance using a second connection (see the `--wal-method=stream` option for `pg_basebackup`). Once the backup is completed, the new instance will be started on a new timeline and diverge from the source. For this reason, it is advised to stop all write operations to the source database before migrating to the target database in Kubernetes. !!! Important Before you attempt a migration, you must test both the procedure and the applications. In particular, it is fundamental that you run the migration procedure as many times as needed to systematically measure the downtime of your applications in production.