Bootstrap

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 "Importing Postgres databases" section.

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 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 "Recovery" section for guidance on each method.

The externalClusters section

The externalClusters section provides a mechanism for specifying one or more PostgreSQL clusters associated with the current configuration. Its 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.

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 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

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.

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 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.

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 type. 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.

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 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 "Locale Support" 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 "Locale Support" 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).

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

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:

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

Executing queries after initialization

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:

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

Bootstrap from another cluster

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).

Bootstrap from a backup (recovery)

Given the several possibilities, methods, and combinations that the CloudNativePG operator provides in terms of backup and recovery, please refer to the "Recovery" section.

Bootstrap from a live cluster (pg_basebackup)

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).

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.

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:

1. via username/password
2. via TLS client certificate

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.

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

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.

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 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.

apiVersion: postgresql.cnpg.io/v1
kind: Cluster
metadata:
  name: target-db
spec:
  instances: 3
  imageName: ghcr.io/cloudnative-pg/postgresql:16.3

  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).

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.

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).

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

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.

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 in Kubernetes.