Database tables not created when flask and postgresql container run together in docker

Question

I have a basic flask application that uses postgresql for database and SQLAlchemy for ORM. I want to deploy this application using docker. The project directory looks something like this:

.
├── app.py
├── database
│   ├── config.py
│   └── models.py
├── docker-compose.yml
├── Dockerfile
└── requirements.txt

I have database table definitions in models.py and database configuration config.py

config.py:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy

app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://flask:flask123@db:5432/flask_db'
db = SQLAlchemy(app)

I then start the app and create database tables with this in app.py

if __name__ == '__main__':
    with app.app_context():
        db.create_all()
        db.session.commit()
        app.run(debug=True)

Dockerfile:

FROM python:3

WORKDIR /app

COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt

COPY . .

EXPOSE 5000

CMD ["flask", "run", "--host", "0.0.0.0"]

docker-compose:

version: "1"
services:
    db:
        image: postgres:latest
        restart: always
        hostname: postgres
        environment: 
            POSTGRES_USER: flask
            POSTGRES_PASSWORD: flask123
            POSTGRES_DB: flask_db
        ports:
            - "5432:5432"
        networks:
            - my_network

    flask_app:
        restart: always
        build:
            context: .
        ports:
            - "5000:5000"
        depends_on:
            - db
        networks:
            - my_network

networks:
    my_network:

When I docker compose up, everything seems to work fine, the containers are up and I can reach my application from localhost:5000. However any api request involving getting data from the database returns an error and when I inspect the database container logs I see the following error for database queries:

ERROR: relation "users" does not exist

I suspect there is something wrong with the connections or the order the containers are started but I cant seem to find what is causing database tables not created.

stackoverflow.com/questions/50938476/… - error might indicate that the user "flask" does not have suitable grants ? — rasjani
– rasjani, Commented Aug 2, 2023 at 12:02
@rasjani I tried to create some tables manually inside the postgres container and when I try to change to user flask it says there is no such user, so it seems like the user is not created at all which I guess can cause the tables not created. But I dont know why the user flask is not created at the first place. — aebosnak
– aebosnak, Commented Aug 2, 2023 at 12:08
I don't believe the if __name__ == "__main__" code is going to run when using flask run. If you want to perform initialization, either use an app factory or register a before_first_request function. — larsks
– larsks, Commented Aug 2, 2023 at 12:55
@larsks Using a before_first_request function solved the problem thanks — aebosnak
– aebosnak, Commented Aug 2, 2023 at 14:14

aebosnak · Accepted Answer · 2023-08-02 14:25:20Z

0

I was trying to start the app with a docker command and inside the app.py file simultaneously. Removing if __name__ == '__main__' and using a before_first_request function as @larsks suggested solved the problem.

Here is the updated part of the app.py file:

@app.before_request
def init_db():
    with app.app_context():
        db.create_all()
        db.session.commit()

answered Aug 2, 2023 at 14:25

aebosnak

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