PostgreSQL Role Management

From its inception, CloudNativePG has managed the creation of specific roles required in PostgreSQL instances:

• some reserved users, such as the postgres superuser, streaming_replica and cnpg_pooler_pgbouncer (when the PgBouncer Pooler is used)
• The application user, set as the low-privilege owner of the application database

This process is described in the "Bootstrap" section.

With the managed stanza in the cluster spec, CloudNativePG now provides full lifecycle management for roles specified in .spec.managed.roles.

This feature enables declarative management of existing roles, as well as the creation of new roles if they are not already present in the database. Role creation will occur after the database bootstrapping is complete.

An example manifest for a cluster with declarative role management can be found in the file cluster-example-with-roles.yaml.

Here is an excerpt from that file:

apiVersion: postgresql.cnpg.io/v1
kind: Cluster
spec:
  managed:
    roles:
    - name: dante
      ensure: present
      comment: Dante Alighieri
      login: true
      superuser: false
      inRoles:
        - pg_monitor
        - pg_signal_backend

The role specification in .spec.managed.roles adheres to the PostgreSQL structure and naming conventions. Please refer to the API reference for the full list of attributes you can define for each role.

A few points are worth noting:

1. The ensure attribute is not part of PostgreSQL. It enables declarative role management to create and remove roles. The two possible values are present (the default) and absent.
2. The inherit attribute is true by default, following PostgreSQL conventions.
3. The connectionLimit attribute defaults to -1, in line with PostgreSQL conventions.
4. Role membership with inRoles defaults to no memberships.

Declarative role management ensures that PostgreSQL instances align with the spec. If a user modifies role attributes directly in the database, the CloudNativePG operator will revert those changes during the next reconciliation cycle.

Password management

The declarative role management feature includes reconciling of role passwords. Passwords are managed in fundamentally different ways in the Kubernetes world and in PostgreSQL, and as a result there are a few things to note.

Managed role configurations may optionally specify the name of a Secret where the username and password are stored (encoded in Base64 as is usual in Kubernetes). For example:

  managed:
    roles:
    - name: dante
      ensure: present
      [… snipped …]
      passwordSecret:
        name: cluster-example-dante

This would assume the existence of a Secret called cluster-example-dante, containing a username and password. The username should match the role we are setting the password for. For example, :

apiVersion: v1
data:
  username: ZGFudGU=
  password: ZGFudGU=
kind: Secret
metadata:
  name: cluster-example-dante
  labels:
    cnpg.io/reload: "true"
type: kubernetes.io/basic-auth

If there is no passwordSecret specified for a role, the instance manager will not try to CREATE / ALTER the role with a password. This keeps with PostgreSQL conventions, where ALTER will not update passwords unless directed to with WITH PASSWORD.

If a role was initially created with a password, and we would like to set the password to NULL in PostgreSQL, this necessitates being explicit on the part of the user of CloudNativePG. To distinguish "no password provided in spec" from "set the password to NULL", the field DisablePassword should be used.

Imagine we decided we would like to have no password on the dante role in the database. In such case we would specify the following:

  managed:
    roles:
    - name: dante
      ensure: present
      [… snipped …]
      disablePassword: true

NOTE: it is considered an error to set both passwordSecret and disablePassword on a given role. This configuration will be rejected by the validation webhook.

Password expiry, VALID UNTIL

The VALID UNTIL role attribute in PostgreSQL controls password expiry. Roles created without VALID UNTIL specified get NULL by default in PostgreSQL, meaning that their password will never expire.

PostgreSQL uses a timestamp type for VALID UNTIL, which includes support for the value 'infinity' indicating that the password never expires. Please see the PostgreSQL documentation for reference.

With declarative role management, the validUntil attribute for managed roles controls password expiry. validUntil can only take:

• a Kubernetes timestamp, or
• be omitted (defaulting to null)

In the first case, the given validUntil timestamp will be set in the database as the VALID UNTIL attribute of the role.

In the second case (omitted validUntil) the operator will ensure password never expires, mirroring the behavior of PostgreSQL. Specifically:

• in case of new role, it will omit the VALID UNTIL clause in the role creation statement
• in case of existing role, it will set VALID UNTIL to infinity if VALID UNTIL was not set to NULL in the database (this is due to PostgreSQL not allowing VALID UNTIL NULL in the ALTER ROLE SQL statement)

Password hashed

You can also provide pre-encrypted passwords by specifying the password in MD5/SCRAM-SHA-256 hash format:

kind: Secret
type: kubernetes.io/basic-auth
metadata:
  name: cluster-example-cavalcanti
  labels:
    cnpg.io/reload: "true"
apiVersion: v1
stringData:
  username: cavalcanti
  password: SCRAM-SHA-256$<iteration count>:<salt>$<StoredKey>:<ServerKey>

Unrealizable role configurations

In PostgreSQL, in some cases, commands cannot be honored by the database and will be rejected. Please refer to the PostgreSQL documentation on error codes for details.

Role operations can produce such fundamental errors. Two examples:

• We ask PostgreSQL to create the role petrarca as a member of the role (group) poets, but poets does not exist.
• We ask PostgreSQL to drop the role dante, but the role dante is the owner of the database inferno.

These fundamental errors cannot be fixed by the database, nor the CloudNativePG operator, without clarification from the human administrator. The two examples above could be fixed by creating the role poets or dropping the database inferno respectively, but they might have originated due to human error, and in such case, the "fix" proposed might be the wrong thing to do.

CloudNativePG will record when such fundamental errors occur, and will display them in the cluster Status. Which segues into…

Status of managed roles

The Cluster status includes a section for the managed roles' status, as shown below:

status:
  […snipped…]
  managedRolesStatus:
    byStatus:
      not-managed:
      - app
      pending-reconciliation:
      - dante
      - petrarca
      reconciled:
      - ariosto
      reserved:
      - postgres
      - streaming_replica
    cannotReconcile:
      dante:
      - 'could not perform DELETE on role dante: owner of database inferno'
      petrarca:
      - 'could not perform UPDATE_MEMBERSHIPS on role petrarca: role "poets" does not exist'

Note the special sub-section cannotReconcile for operations the database (and CloudNativePG) cannot honor, and which require human intervention.

This section covers roles reserved for operator use and those that are not under declarative management, providing a comprehensive view of the roles in the database instances.

The kubectl plugin also shows the status of managed roles in its status sub-command:

Managed roles status
Status                  Roles
------                  -----
pending-reconciliation  petrarca
reconciled              app,dante
reserved                postgres,streaming_replica

Irreconcilable roles
Role      Errors
----      ------
petrarca  could not perform UPDATE_MEMBERSHIPS on role petrarca: role "poets" does not exist