Bootstrap

This section describes the options available 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 provides the option to import one or more databases from an existing PostgreSQL cluster, even if it’s outside Kubernetes or running a different major version of PostgreSQL. For more detailed information about this feature, please refer to the Importing Postgres databases section.

Note

Bootstrapping from an existing cluster enables the creation of a replica cluster—an independent PostgreSQL cluster that remains in continuous recovery, stays synchronized with the source cluster, and accepts read-only connections. For more details, refer to the Replica Cluster section .

Warning

CloudNativePG requires both the postgres user and database to always exist. Using the local Unix Domain Socket, it needs to connect as the 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!!!

Note

CloudNativePG is gradually introducing support for Kubernetes' native `VolumeSnapshot API <https://github.com/cloudnative-pg/cloudnative-pg/issues/2081>`_

for both incremental and differential copy in backup and recovery operations - if supported by the underlying storage classes. Please see Recovery from Volume Snapshot objects

for details.

The bootstrap section

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 through the streaming replication protocol. This method is particularly useful for migrating databases to CloudNativePG, although meeting all requirements can be challenging. Be sure to review the warnings in the Bootstrap from a live cluster (`pg_basebackup ) <Bootstrap from a live cluster (pg_basebackup )>`

carefully.

Only one bootstrap method can be specified in the manifest. Attempting to define multiple bootstrap methods will result in validation errors.

In contrast to 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. Refer to the replica cluster section for more information.

Given the amount of possible backup methods and combinations of backup storage that the CloudNativePG operator provides for recovery , please refer to the dedicated Recovery from an object store for guidance on each method.

Note

Please refer to the "API reference for the `bootstrap section <Bootstrap>`

for more information.

The externalClusters section

The externalClusters section of the cluster manifest can be used to configure access to one or more PostgreSQL clusters as sources. The primary use cases include:

1. Importing Databases: Specify an external source to be utilized during the importation of databases via logical backup and restore, as part of the initdb bootstrap method.

2. 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.

3. Recovery from Physical Base Backup: Recover, fully or at a given Point-In-Time, a PostgreSQL cluster by referencing a physical base backup.

Note

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 one. An external cluster needs to have:

• a name that identifies the external 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, Azure Blob Storage, or 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. The following table summarizes your options:

Content of externalClusters	pg_basebackup	recovery
Only streaming	✓
Only object store		✓
Streaming and object store	✓	✓

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.

Note

Please refer to the "API reference for the `externalClusters section <API Reference>`

for more information.

Password files

Whenever a password is supplied within an externalClusters entry, CloudNativePG autonomously manages a PostgreSQL password file

for it, residing at /controller/external/NAME/pgpass in each instance.

This approach enables 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.

Bootstrap an empty cluster (initdb )

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:

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:

1. create a new PGDATA folder using PostgreSQL’s native initdb command

2. create an unprivileged user named app

3. 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 )

4. 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 kubernetes.io/basic-auth . 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:

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.

Note

If you need to create additional users, please refer to Declarative database role management .

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.

Passing Options to initdb

The PostgreSQL data directory is initialized using the initdb .

CloudNativePG enables you to customize the behavior of initdb to modify settings such as default locale configurations and data checksums.

Warning

CloudNativePG acts only as a direct proxy to initdb for locale-related options, due to the ongoing and significant enhancements in PostgreSQL's locale support. It is your responsibility to ensure that the correct options are provided, following the PostgreSQL documentation, and to verify that the bootstrap process completes successfully.

To include custom options in the initdb command, you can use the following parameters:

builtinLocale

When builtinLocale is set to a value, CloudNativePG passes it to the --builtin-locale option in initdb . This option controls the builtin locale, as defined in Locale Support

from the PostgreSQL documentation (default: empty). Note that this option requires localeProvider to be set to builtin . Available from PostgreSQL 17.

dataChecksums

When dataChecksums is set to true , CloudNativePG 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, CloudNativePG passes it to the --encoding option in initdb , which selects the encoding of the template database (default: UTF8 ).

icuLocale

When icuLocale is set to a value, CloudNativePG passes it to the --icu-locale option in initdb . This option controls the ICU locale, as defined in Locale Support

from the PostgreSQL documentation (default: empty). Note that this option requires localeProvider to be set to icu . Available from PostgreSQL 15.

icuRules

When icuRules is set to a value, CloudNativePG passes it to the --icu-rules option in initdb . This option controls the ICU locale, as defined in Locale Support from the PostgreSQL documentation (default: empty). Note that this option requires localeProvider to be set to icu . Available from PostgreSQL 16.

locale

When locale is set to a value, CloudNativePG passes it to the --locale option in initdb . This option controls the locale, as defined in Locale Support from the PostgreSQL documentation. By default, the locale parameter is empty. In this case, environment variables such as LANG are used to determine the locale. Be aware that these variables can vary between container images, potentially leading to inconsistent behavior.

localeCollate

When localeCollate is set to a value, CloudNativePG passes it to the --lc-collate option in initdb . This option controls the collation order (LC_COLLATE subcategory), as defined in Locale Support

from the PostgreSQL documentation (default: C ).

localeCType

When localeCType is set to a value, CloudNativePG passes it to the --lc-ctype option in initdb . This option controls the collation order (LC_CTYPE subcategory), as defined in Locale Support

from the PostgreSQL documentation (default: C ).

localeProvider

When localeProvider is set to a value, CloudNativePG passes it to the --locale-provider option in initdb . This option controls the locale provider, as defined in Locale Support from the PostgreSQL documentation (default: empty, which means libc for PostgreSQL). Available from PostgreSQL 15.

walSegmentSize

When walSegmentSize is set to a value, CloudNativePG 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 LC_COLLATE and LC_TYPE subcategories. The remaining locale subcategories can be configured directly in the PostgreSQL configuration, using the lc_messages , lc_monetary , lc_numeric , and lc_time parameters.

The following example enables data checksums and sets the default encoding to LATIN1 :

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.

Executing Queries After Initialization

You can specify a custom list of queries that will be executed once, immediately after the cluster is created and configured. These queries will be executed as the superuser (postgres ) against three different databases, in this specific order:

1. The postgres database (postInit section)

2. The template1 database (postInitTemplate section)

3. The application database (postInitApplication section)

For each of these sections, CloudNativePG provides two ways to specify custom queries, executed in the following order:

• As a list of SQL queries in the cluster’s definition (postInitSQL , postInitTemplateSQL , and postInitApplicationSQL stanzas)

• As a list of Secrets and/or ConfigMaps, each containing a SQL script to be executed (postInitSQLRefs , postInitTemplateSQLRefs , and postInitApplicationSQLRefs stanzas). Secrets are processed before ConfigMaps.

Objects in each list will be processed sequentially.

Warning

Use the postInit , postInitTemplate , and postInitApplication options with extreme care, as queries are run as a superuser and can disrupt the entire cluster. An error in any of those queries will interrupt the bootstrap phase, leaving the cluster incomplete and requiring manual intervention.

Note

Ensure the existence of entries inside the ConfigMaps or Secrets specified in postInitSQLRefs , postInitTemplateSQLRefs , and postInitApplicationSQLRefs , otherwise the bootstrap will fail. Errors in any of those SQL files will prevent the bootstrap phase from completing successfully.

The following example runs a single SQL query as part of the postInitSQL stanza:

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

The example below relies on postInitApplicationSQLRefs to specify a secret and a ConfigMap containing the queries to run after the initialization on the application database:

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

Within SQL scripts, each SQL statement is executed in a single exec on the server according to the PostgreSQL semantics . Comments can be included, but internal commands like psql cannot.

Bootstrap from another cluster

CloudNativePG enables bootstrapping a cluster starting from another one of the same major version. This operation can be carried out either 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).

Note

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. Backup plugins provide ways to specify a different one. For example, the Barman Cloud Plugin provides the serverName

(by default assigned to the value of name in the external cluster definition).

Bootstrap from a backup (recovery )

Given the variety of backup methods and combinations of backup storage options provided by the CloudNativePG operator for recovery , please refer to the dedicated Recovery from an object store for detailed guidance on each method.

Bootstrap from a live cluster (pg_basebackup )

The pg_basebackup bootstrap mode allows you to create a new cluster (target) as an exact physical copy of an existing and binary-compatible PostgreSQL instance (source) managed by CloudNativePG, using a valid streaming replication connection. The source instance can either be a primary or a standby PostgreSQL server. It’s crucial to thoroughly review the requirements section below, as the pros and cons of PostgreSQL physical replication fully apply.

The primary use cases for this method include:

• Reporting and business intelligence clusters that need to be regenerated periodically (daily, weekly)

• Test databases containing live data that require periodic regeneration (daily, weekly, monthly) and anonymization

• Rapid spin-up of a standalone replica cluster

• Physical migrations of CloudNativePG clusters to different namespaces or Kubernetes clusters

Note

Avoid using this method, based on physical replication, to migrate an existing PostgreSQL cluster outside of Kubernetes into CloudNativePG, unless you are completely certain that all Requirements are met and the operation has been thoroughly tested. The CloudNativePG community does not endorse this approach for such use cases, and recommends using logical import instead. It is exceedingly rare that all requirements for physical replication are met in a way that seamlessly works with CloudNativePG.

Warning

In its current implementation, this method clones the source PostgreSQL instance, thereby creating a snapshot. Once the cloning process has finished, the new cluster is immediately started. Refer to Current limitations for more details.

Similar to the recovery bootstrap method, once the cloning operation is complete, the operator takes full ownership of the target cluster, starting from the first instance. This includes overriding certain configuration parameters as required by CloudNativePG, resetting the superuser password, creating the streaming_replica user, managing replicas, and more. The resulting cluster operates independently from the source instance.

Note

Configuring the network connection between the target and source instances lies outside the scope of CloudNativePG documentation, as it depends heavily on the specific context and environment.

The streaming replication client on the target instance, managed transparently by pg_basebackup , can authenticate on the source instance using one of the following methods:

1. Username/Password authentication

2. TLS certificate authentication

Both authentication methods are detailed below.

Requirements

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 max_wal_senders 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 About the replication user below)

• target must be able to successfully connect to the source PostgreSQL instance using a role with REPLICATION LOGIN privileges

Note

For further information, please refer to the Planning , the pg_basebackup

and the High Availability, Load Balancing, and Replication

in the PostgreSQL documentation.

About the replication user

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:

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.

Username/Password authentication

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:

##  A more restrictive rule for TLS and IP of origin is recommended

host replication streaming_replica all md5

The following manifest creates a new PostgreSQL 18.1 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.

apiVersion: postgresql.cnpg.io/v1
kind: Cluster
metadata:
  name: target-db
spec:
  instances: 3
  imageName: ghcr.io/cloudnative-pg/postgresql:18.1-system-trixie

  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 18.1).

TLS certificate authentication

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 18.1 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).

apiVersion: postgresql.cnpg.io/v1
kind: Cluster
metadata:
  name: cluster-clone-tls
spec:
  instances: 3
  imageName: ghcr.io/cloudnative-pg/postgresql:18.1-system-trixie

  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

Configure the application database

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.

Note

While the Cluster is in recovery mode, no changes to the database, including the catalog, are permitted. This restriction includes any role overrides, which are deferred until the Cluster transitions to primary. During the recovery phase, roles remain as defined in the source cluster.

The example below configures the app database with the owner app and the password stored in the provided secret app-secret , following the bootstrap from a live cluster.

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 only after recovery is completed:

1. If the app database does not exist, it will be created.

2. If the app user does not exist, it will be created.

3. If the app user is not the owner of the app database, ownership will be granted to the app user.

4. If the username value matches the owner value in the secret, the password for the application user (the app user in this case) will be updated to the password value in the secret.

Current limitations

Snapshot copy

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.

Note that this limitation applies only if the target cluster is not defined as a replica cluster.

Note

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.