README.md

postgresql_client

Usage

This relation interface describes the expected behaviour of any charm claiming to be able to interact with a PostgreSQL database. Our intent to have different interface names with <database>_client pattern (like mongodb_client) and the same validation rules for multiple databases (e.g. MySQL, PostgreSQL, MongoDB, etc).

In most cases, this will be accomplished using the data_interfaces library, although charm developers are free to provide alternative libraries as long as they fulfil the behavioural and schematic requirements described in this document.

Some Providers may be subordinate charms aimed at providing mainly a local service within a principal. In cases where the Requirer needs to expose the service beyond its host, it should request for external connectivity by the Provider. An example use case would be the data-integrator charm integrating with a subordinate router.

Direction

flowchart TD
    Requirer -- database, \nextra-user-roles, \nrequested-secrets, \nexternal-node-connectivity --> Provider
    Provider -- database, \nendpoints, \nsecret-user, \nsubordinated, \nstate--> Requirer

Loading

As with all Juju relations, the database interface consists of two parties: a Provider (database charm), and a Requirer (application charm). The Requirer will be expected to provide a database name, and the Provider will provide new unique credentials (along with other optional fields), which can be used to access the actual database cluster.

Behavior

Both the Requirer and the Provider need to adhere to criteria to be considered compatible with the interface.

If both sides support Juju Secrets, sensitive information is transmitted through Juju Secrets rather than directly through the relation data bag(s). Corresponding pieces of information are grouped together in a single secret. If any side, Provider or Requirer doesn't support Juju Secrets, sensitive information is transmitted through the relational data bag in the same fields as in Juju Secret.

Provider

• Is expected to create an application user inside the database cluster when the requirer provides the database field.
• Is expected to provide credentials (username and password) in a Juju Secret whenever the Requirer supplies the database field.
• Is expected to expose the Juju Secrets URI to the credentials through the secret-user field of the data bag.
• Is expected to provide the endpoints field with the address of Primary, which can be used for Read/Write queries.
• Is expected to provide the database field with the database that was actually created.
• Is expected to provide the uris field with the connection string, in libpq's URI format, which can be used for direct connection to the db.
• Is expected to provide optional read-only-endpoints field with a comma-separated list of hosts or one Kubernetes Service, which can be used for Read-only queries.
• Is expected to provide the version field whenever database charm wants to communicate its database version.
• Is expected to provide the CA chain in the tls-ca field of a Juju Secret, whenever the provider has TLS enabled (such as using the TLS Certificates Operator).
• Is expected to share the TLS Juju Secret URI through the secret-tls field of the databag.
• If the Requirer asks for additional secrets (via requested-secrets, see below) other than those stored in the user and tls secrets, Provider is expected to define a secret-extra field holding the URI of the Juju Secret containing all additional secret fields.
• Is expected to express (via external-node-connectivity) whether external connectivity requests are to be respected or not, in case the charm is capable of such.
• May require delays (via subordinated) to provide service on Requirer scale up. If so, it is expected to set unit level state data when it is ready to serve.

Requirer

• Is expected to provide requested-secrets, which is a list of field names that are not to be exposed on the relation databag, but handled within Juju Secrets. It should be JSON parsable array of strings, and correspond to valid Juju Secret keys (i.e. alphanumerical characters with a potential '-' (dash) character). Secret fields must contain username and password (and tls-ca in case TLS is enabled).
• Is expected to provide a database name in the database field.
• Is expected to have unique credentials for each relation. Therefore, different instances of the same Charm (juju applications) will have different relations with different credentials.
• Is expected to have different relations names on Requirer with the same interface name if Requirer needs access to multiple database charms.
• Is expected to allow multiple different Juju applications to access the same database name.
• Is expected to add any extra-user-roles provided by the Requirer to the created user (e.g. extra-user-roles=admin).
• Is expected to tolerate that the Provider may ignore the database field in some cases and instead use the database name received.
• Is expected to respect the subordinated flag when scaling up and start emitting events only once unit level state is ready.
• May require external connectivity (via external-node-connectivity).

Relation Data

Provider

[JSON Schema]

Provider provides credentials, endpoints, TLS info and database-specific fields. It should be placed in the application databag.

Example

  relation-info:
  - endpoint: database
    related-endpoint: database
    application-data:
      database: myappB
      endpoints: postgresql-k8s-primary:5432
      read-only-endpoints: postgresql-k8s-replicas:5432
      secret-user: secret://59060ecc-0495-4a80-8006-5f1fc13fd783/cjqub6vubg2s77p3nio0
      secret-tls: secret://59060ecc-0495-4a80-8006-5f1fc13fd783/cjqub7fubg2s77p3niog

Requirer

[JSON Schema]

Requirer provides database name. It should be placed in the application databag.

Example

  relation-info:
  - endpoint: database
    related-endpoint: database
    application-data:
      database: myappA
    requested-secrets: ["username", "password", "tls-ca", "uris"]