Using Docker postgres image with flask

Agenda

This is a follow up from our last post which created a Flask polls app.

In last post, the flask app connected to a postgres server running on the host. Our application had a single Docker container.

In this post we will run Postgres on a Docker container too.

This has an advantage that developers don’t need to have postgres installed on the host machine. Simultaneously we want the postgres data to persist even after the containers are destroyed.

Our code would remain unchanged in this post. Check the last post to get code familiarity.

Docker services

In last post we had a single service called flask. In this post we will add an additional service called db. Also we will rename flask to web.

Your directory structure would look like:

├── Dockerfile
├── README.md
├── __init__.py
├── app.py
├── db.py
├── docker-compose.yml
├── env.list
├── models.py
├── requirements.txt
├── settings.py
└── tox.ini

docker-compose.yml should look like:

version: '3'
services:
    web:
        build: .
        command: flask run --host=0.0.0.0 --port=8000
        ports:
            - 8000:8000
        environment:
            - FLASK_APP=app.py
        env_file:
            - env.list
        depends_on:
            - db
    db:
        image: postgres
        environment:
            - POSTGRES_USER=polls
            - POSTGRES_PASSWORD=hearmeroar
            - POSTGRES_DB=polls_db
        volumes:
            - flask_polls_data:/var/lib/postgresql/data

volumes:
    flask_polls_data:

Service web is largely unchanged from last post.

We used official postgres image provided by Docker. We set some environment variables to set database name and credentials.

Flask app would be connecting to this database now so we need to edit env.list accordingly:

DB_HOST=db
DB_PORT=5432
DB_NAME=polls_db
DB_USER=polls
DB_PASSWORD=hearmeroar

Notice how we changed DB_HOST from localhost to db. We named it db because of service name is db in docker-compose.yml.

We used volumes to persist our data.

Start the services:

docker-compose up

You should be able to create a question and list questions.

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