How to integrate a database with my charm

Check supported interfaces

First, we recommend that you check the supported interfaces of the current charm. You have options to use modern (preferred) or legacy interfaces.

Most existing charms currently use ops-lib-pgsql interface (legacy). For new charms, Canonical recommends using data-platform-libs instead.

Legacy charm details are described here.

Integrate

For an introduction to the concepts of Juju integrations, see Juju | Integration.

For a detailed tutorial about integrating your charm with the PostgreSQL charm, refer to Juju | Integrate your charm with PostgreSQL.

For some practical examples, take a look at the GitHub repositories

• postgresql-test-app
• juju-sdk-tutorial-k8s - the branch 04_integrate_with_psql describes integration with Charmed PostgreSQL K8s

FAQ

Does the requirer need to set anything in relation data?

It depends on the interface. Check the postgresql_client interface requirements.

Is there a charm library available, or does my charm need to compile the postgresql relation data on its own?

Yes, the library is available: data-platform-libs. The integration is trivial: example.

How do I obtain the database url/uri?

This feature is planned but currently missing.

Meanwhile, use this example or refer to the function below.

def _db_connection_string(self) -> str:
   """Report database connection string using info from relation databag."""
   relation = self.model.get_relation("database")
   if not relation:
       return ""

   data = self._database.fetch_relation_data()[relation.id]
   username = data.get("username")
   password = data.get("password")
   endpoints = data.get("endpoints")
   
   return f"postgres://{username}:{password}@{endpoints}/ratings"

Troubleshooting

• Start with Juju | How to debug a charm.
• Check Charmed PostgreSQL VM | Troubleshooting.

Success stories:

• How to migrate Nextcloud to new PostgreSQL (vm-charms).

Contact us if you have any questions, issues, or ideas!