PostgreSQL Database Management

CloudNativePG simplifies PostgreSQL database provisioning by automatically creating an application database named app by default. This default behavior is explained in the "Bootstrap an Empty Cluster" section.

For more advanced use cases, CloudNativePG introduces declarative database management, which empowers users to define and control the lifecycle of PostgreSQL databases using the Database Custom Resource Definition (CRD). This method seamlessly integrates with Kubernetes, providing a scalable, automated, and consistent approach to managing PostgreSQL databases.

Key Concepts

Scope of Management

Important

CloudNativePG manages global objects in PostgreSQL clusters, such as databases, roles, and tablespaces. However, it does not manage the content of databases (e.g., schemas and tables). For database content, specialized tools or the applications themselves should be used.

Declarative `Database` Manifest

The following example demonstrates how a Database resource interacts with a Cluster:

apiVersion: postgresql.cnpg.io/v1
kind: Database
metadata:
  name: cluster-example-one
spec:
  name: one
  owner: app
  cluster:
    name: cluster-example

When applied, this manifest creates a Database object called cluster-example-one requesting a database named one, owned by the app role, in the cluster-example PostgreSQL cluster.

Info

Please refer to the API reference the full list of attributes you can define for each Database object.

Required Fields in the `Database` Manifest

metadata.name: Unique name of the Kubernetes object within its namespace.
spec.name: Name of the database as it will appear in PostgreSQL.
spec.owner: PostgreSQL role that owns the database.
spec.cluster.name: Name of the target PostgreSQL cluster.

The Database object must reference a specific Cluster, determining where the database will be created. It is managed by the cluster's primary instance, ensuring the database is created or updated as needed.

Info

The distinction between metadata.name and spec.name allows multiple Database resources to reference databases with the same name across different CloudNativePG clusters in the same Kubernetes namespace.

Reserved Database Names

PostgreSQL automatically creates databases such as postgres, template0, and template1. These names are reserved and cannot be used for new Database objects in CloudNativePG.

Important

Creating a Database with spec.name set to postgres, template0, or template1 is not allowed.

Reconciliation and Status

Once a Database object is reconciled successfully:

status.applied will be set to true.
status.observedGeneration will match the metadata.generation of the last applied configuration.

Example of a reconciled Database object:

apiVersion: postgresql.cnpg.io/v1
kind: Database
metadata:
  generation: 1
  name: cluster-example-one
spec:
  cluster:
    name: cluster-example
  name: one
  owner: app
status:
  observedGeneration: 1
  applied: true

If an error occurs during reconciliation, status.applied will be false, and an error message will be included in the status.message field.

Deleting a Database

CloudNativePG supports two methods for database deletion:

Using the delete reclaim policy
Declaratively setting the database's ensure field to absent

Deleting via `delete` Reclaim Policy

The databaseReclaimPolicy field determines the behavior when a Database object is deleted:

retain (default): The database remains in PostgreSQL for manual management.
delete: The database is automatically removed from PostgreSQL.

Example:

apiVersion: postgresql.cnpg.io/v1
kind: Database
metadata:
  name: cluster-example-two
spec:
  databaseReclaimPolicy: delete
  name: two
  owner: app
  cluster:
    name: cluster-example

Deleting this Database object will automatically remove the two database from the cluster-example cluster.

Declaratively Setting `ensure: absent`

To remove a database, set the ensure field to absent like in the following example:.

apiVersion: postgresql.cnpg.io/v1
kind: Database
metadata:
  name: cluster-example-database-to-drop
spec:
  cluster:
    name: cluster-example
  name: database-to-drop
  owner: app
  ensure: absent

This manifest ensures that the database-to-drop database is removed from the cluster-example cluster.

Limitations and Caveats

Renaming a database

While CloudNativePG adheres to PostgreSQL’s CREATE DATABASE and ALTER DATABASE commands, renaming databases is not supported. Attempting to modify spec.name in an existing Database object will result in rejection by Kubernetes.

Creating vs. Altering a Database

For new databases, CloudNativePG uses the CREATE DATABASE statement.
For existing databases, ALTER DATABASE is used to apply changes.

It is important to note that there are some differences between these two Postgres commands: in particular, the options accepted by ALTER are a subset of those accepted by CREATE.

Warning

Some fields, such as encoding and collation settings, are immutable in PostgreSQL. Attempts to modify these fields on existing databases will be ignored.

Replica Clusters

Database objects declared on replica clusters cannot be enforced, as replicas lack write privileges. These objects will remain in a pending state until the replica is promoted.

Conflict Resolution

If two Database objects in the same namespace manage the same PostgreSQL database (i.e., identical spec.name and spec.cluster.name), the second object will be rejected.

Example status message:

status:
  applied: false
  message: 'reconciliation error: database "one" is already managed by Database object "cluster-example-one"'

Postgres Version Differences

CloudNativePG adheres to PostgreSQL's capabilities. For example, features like ICU_RULES introduced in PostgreSQL 16 are unavailable in earlier versions. Errors from PostgreSQL will be reflected in the Database object's status.

Manual Changes

CloudNativePG does not overwrite manual changes to databases. Once reconciled, a Database object will not be reapplied unless its metadata.generation changes, giving flexibility for direct PostgreSQL modifications.