deploy-flask.rst

How to configure an existing Flask application for deployment on Divio

The steps here should work with any Flask application, and include configuration for:

• Postgres or MySQL database
• cloud media storage using S3
• static file handling using WhiteNoise
• configuring a gateway server.

For a Flask application, you can use:

FROM python:3.8

Here, python:3.8 is the name of the Docker base image. We cannot advise on what base image you should use; you'll need to use one that is in-line with your application's needs. However, once you have a working set-up, it's good practice to move to a more specific base image - for example python:3.8.1-slim-buster.

# install dependencies listed in the repository's requirements file
RUN pip install -r requirements.txt

The requirements.txt file should pin Python dependencies as firmly possible (use the output from pip freeze to get a full list). You will probably need to include some of the following:

# Select one of the following for the database as required
psycopg2==2.8.5
mysqlclient==2.0.1

# Select one of the following for the gateway server
uwsgi==2.0.19.1
gunicorn==20.0.4

Check that the version of Flask is correct, and include any other Python components required by your application.

# Select one of the following application gateway server commands
CMD uwsgi --http=0.0.0.0:80 --module="flaskr:create_app()"
CMD gunicorn --bind=0.0.0.0:80 --forwarded-allow-ips="*" "flaskr:create_app()"

There are various Python helper module libraries available that can parse environment variables to extract the settings so that you can apply them to the application.

Your own application should do something similar if it needs to use the database.

One option for Flask is to configure the web server/gateway server to handle them; using Flask's own send_from_directory() can also be used, or :doc:`whitenoise:index` - see :doc:`whitenoise:flask`.

version: "2.4"
services:
  web:
    # the application's web service (container) will use an image based on our Dockerfile
    build: "."
    # map the internal port 80 to port 8000 on the host
    ports:
      - "8000:80"
    # map the host directory to app (which allows us to see and edit files inside the container)
    volumes:
      - ".:/app:rw"
      - "./data:/data:rw"
    # the default command to run whenever the container is launched
    command: flask run --host=0.0.0.0 --port=80
    # a link to database_default, the application's local database service
    links:
      - "database_default"
    env_file: .env-local

  database_default:
    # Select one of the following db configurations for the database
    image: postgres:13.5-alpine
    environment:
      POSTGRES_DB: "db"
      POSTGRES_HOST_AUTH_METHOD: "trust"
      SERVICE_MANAGER: "fsm-postgres"
    volumes:
      - ".:/app:rw"

    image: mysql:5.7
    environment:
      MYSQL_DATABASE: "db"
      MYSQL_ALLOW_EMPTY_PASSWORD: "yes"
      SERVICE_MANAGER: "fsm-mysql"
    volumes:
      - ".:/app:rw"
      - "./data/db:/var/lib/mysql"
    healthcheck:
        test: "/usr/bin/mysql --user=root -h 127.0.0.1 --execute \"SHOW DATABASES;\""
        interval: 2s
        timeout: 20s
        retries: 10

The FLASK_APP variable is used by the flask run command. It assumes that your application can be found at flaskr; amend this appropriately if required.

# Select one of the following for the database
DATABASE_URL=postgres://postgres@database_default:5432/db
DATABASE_URL=mysql://root@database_default:3306/db

DEFAULT_STORAGE_DSN=file:///data/media/?url=%2Fmedia%2F
DOMAIN_ALIASES=localhost, 127.0.0.1
SECURE_SSL_REDIRECT=False

FLASK_APP=flaskr
FLASK_ENV=development

If using the suggestions above, you'll probably want:

# Python
*.pyc
*.pyo
db.sqlite3

# Divio
.divio
/data.tar.gz
/data


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