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How to interact with your application's database

The database for your Divio application runs:

In either case, you will mostly only need to interact with the database using the tools provided by your application's runtime stack (e.g. Django). However, if you need to interact with it directly, the option exists.

The database service name in docker-compose.yml

The Divio CLI expects that the database service will be named database_default (or db) in your docker-compose.yml file. If not, it certain commands (such as divio app push/pull db) will fail.

Interact with the local database​

Generally, the most convenient way to interact with the application's database is to do it locally (with a local copy of your cloud data if necessary).

From the application's local Django web container​

Using dbshell​

Run:

docker compose run --rm web python ./manage.py dbshell

Connecting to a Postgres database manually​

You can also make the connection manually from within the web container, for example:

docker compose run --rm web psql -h database_default -U postgres db

The -h value (for host) needs to match the name of the database service in the docker-compose.yml file, which might be different (for example, database_default).

As well as psql you can run commands such as pg_dump and pg_restore. This is useful for a number of common operations, below.

Your application may not have the psql client installed already, in which case you will need to install it first. See How to install system packages in an application.

Using docker exec​

Another way of interacting with the database is via the database container itself, using docker exec. This requires that the database container already be up and running.

For example, if your database container is called example_database_default_1:

docker exec -i example_database_default_1 psql -U postgres

From your host environment​

If you have a preferred database management tool that runs on your own computer, you can also connect to the database from outside the application.

Expose the database's port to the host​

In order to the connect to the database from a tool running directly on your own machine, you will need to expose its port (5432 by default for Postgres).

Add a ports section to the database service in docker-compose.yml and map the port to your host. For Postgres, for example:

database_default:
  image: postgres:15.7-alpine
  ports:
    - 5432:5432

This means that external traffic reaching the container on port 5432 will be routed to port 5432 internally.

The ports are <host port>:<container port> - you can choose another host port if you are already using that port on your host.

Now restart the database container with: docker compose up -d database_default

Connect to a Postgres database​

You will need to use the following details:

  • port: 5432
  • username: postgres
  • password: not required
  • database: db

Access the database using your Postgres tool of choice. Note that you must specify the host address, 127.0.0.1.

For example, if you're using the psql command line tool, you can connect to the application database with:

psql -h 127.0.0.1 -U postgres db

Interact with the Cloud database​

Use the divio app pull db and divio app push db commands to copy a database between a cloud environment and your own local environment.

Note that the pull operation downloads a binary database dump (in a tarred archive), whereas push creates and uploads a SQL database dump.

See the divio CLI command reference for more on using these commands.

From the Cloud application's container​

Log into your Cloud application's container (Test or Live) over SSH.

Using dbshell in a Django application​

Run:

./manage.py dbshell

This will drop you into a command-line client, connected to your database.

Connecting to a database manually​

You can also make the connection manually. Run env to list your environment variables. Amongst them you'll find DATABASE_URL, which will be in the form:

schema://<user name>:<password>@<address>:<port>/<name>

You can use these credentials in the appropriate client, e.g. psql.

From your own computer​

Access to cloud databases other than from the associated application containers is not possible - it is restricted, for security reasons, to containers running on our own infrastructure.

Change the local database engine version​

Sometimes, you will need to change the database engine, or its version number, that your local application uses - for example if the cloud database is updated or changed. If the two database engines are not the same, you may run into problems.

The local database engine is specified by the image option in the database service (usually called database_default in your application's docker-compose.yml file, for example:

database_default:
  image: postgres:15.7-alpine

Should you need to change this, that line should be updated - for example if the Cloud database is now running Postgres 16:

database_default:
  image: postgres:16-alpine

Docker will use the new version the next time the local application is launched.

If you are not sure what image to use for the local database, Divio support will be able to advise you.

important

In the Divio architecture, the docker-compose.yml file is not used for Cloud deployments, but only for the local server. The changes you make here will not affect the Cloud database.

Manage Postgres extensions​

Although you cannot create extensions yourself on our shared database clusters, we can often enable extensions for you on request. The most commonly-requested of these is PostGIS. Please contact Divio support for this.

You will run into errors if you perform an operation that requires or tries to create a missing extension, for example:

psycopg2.errors.InsufficientPrivilege: permission denied to create extension "unaccent"

from a database migration or

---> Processing error!

from a divio push db command, when the local database uses an extension not available on the cloud.

Run the Postgres \dx command in a local database shell or in a cloud shell to list extensions that you're using.

Usage examples for common basic operations​

It's beyond the scope of this article to give general guidance on using the database, but these examples will help give you an idea of some typical operations that you might undertake while using Divio.

All the examples assume that you are interacting with the local database, running in its db container, and will use Postgres.

In each case, we launch the command from within the web container with docker compose run --rm web and we specify:

  • host name: -h database_default
  • user name: -U postgres

Dump the database​

From the web service, dump the database db to a file named database.dump:

docker compose run --rm web pg_dump -h database_default -U postgres db > database.dump

Drop the database​

Drop (delete) the database named db:

docker compose run --rm web dropdb -h database_default -U postgres db

Create the database​

Create a database named db:

docker compose run --rm web createdb -h database_default -U postgres db

Apply the hstore extension​

Apply the hstore extension (required on a newly-created local database) to the database named db:

docker compose run --rm web psql -h database_default -U postgres db -c "CREATE EXTENSION hstore"

Restore the database​

Restore a database named db from a file named database.dump:

docker compose run --rm web pg_restore -h database_default -U postgres -d db database.dump --no-owner

Reset the database​

To reset the database (with empty tables, but the schema in place) you would run the commands above to drop and create the database, create the the hstore extension, followed by a migration:

docker compose run --rm web python manage.py migrate

Restore from a downloaded Cloud backup​

Untar the downloaded backup.tar file. It contains a database.dump file. Copy the file to your local application directory, then run the commands above to drop and create the database, create the the hstore extension, and then restore from a file.