Setup reverse proxy Python Flask

Setup reverse proxy Python Flask

This example adds a Python 3.12 Flask service with a Devilbox Docker Compose override, then proxies the project virtual host to the Flask container.

Overview

Project name	Container path	Database	TLD_SUFFIX	Project URL
my-flask	/shared/httpd/my-flask	none	lvh.me	http://my-flask.lvh.me / https://my-flask.lvh.me

The Flask application listens on port 3000. The reverse-proxy templates forward traffic to the Flask backend defined by the compose override.

Required configuration

Service	Notes
Webserver	Reverse-proxy vhost-gen templates must be copied into the project.
Python Flask	The Flask compose override must be active.
.env	FLASK_PROJECT=my-flask and PYTHON_VERSION=3.12 must be set.

Start from a stopped stack when adding the override:

./dvl.sh down

Walk through

It will be ready in ten steps:

1. Configure Flask project name and Python version.
2. Enter the PHP container.
3. Create a new virtual host directory.
4. Create the Flask application.
5. Link a placeholder docroot.
6. Add reverse-proxy vhost-gen config files.
7. Enable the Flask compose override.
8. Verify DNS.
9. Start Devilbox.
10. Open the project in a browser.

1. Configure Flask project and Python version

Add the variables to the end of .env:

FLASK_PROJECT=my-flask
PYTHON_VERSION=3.12

2. Enter the PHP container

Start the base services before creating files, then enter the PHP container:

./dvl.sh up php httpd bind
./dvl.sh shell php83

3. Create the vhost directory

mkdir -p /shared/httpd/my-flask
cd /shared/httpd/my-flask

4. Create the Flask application

Create the application source:

mkdir app
vi app/main.py

"""Flask example application."""
from flask import Flask

app = Flask(__name__)


@app.route("/")
def index():
    """Serve the default index page."""
    return "Hello from Flask on Python 3.12!"


if __name__ == "__main__":
    app.run(host="0.0.0.0", port=3000)

Add dependencies:

cat > requirements.txt <<'REQ'
Flask>=3.0,<4.0
REQ

5. Link a placeholder docroot

ln -s app htdocs

6. Add reverse-proxy vhost-gen config files

Leave the shell and copy templates from the Devilbox directory:

exit
cd /path/to/devilbox
mkdir -p data/www/my-flask/.devilbox
cp cfg/vhost-gen/apache22.yml-example-rproxy data/www/my-flask/.devilbox/apache22.yml
cp cfg/vhost-gen/apache24.yml-example-rproxy data/www/my-flask/.devilbox/apache24.yml
cp cfg/vhost-gen/nginx.yml-example-rproxy data/www/my-flask/.devilbox/nginx.yml

Edit each template to forward to the Flask backend and port 3000. If your override keeps the historical static backend IP, the Apache templates should contain:

ProxyPass / http://172.16.238.250:3000/
ProxyPassReverse / http://172.16.238.250:3000/

The Nginx template should contain:

location / {
  proxy_set_header Host $host;
  proxy_set_header X-Real-IP $remote_addr;
  proxy_pass http://172.16.238.250:3000;
}

If you customize the compose service name or network, use that backend instead of the static IP.

7. Enable the Flask compose override

Copy the Flask override into place or merge it with your existing override:

cp compose/docker-compose.override.yml-python-flask.yml docker-compose.override.yml

Caution

If docker-compose.override.yml already contains local changes, merge the Flask service instead of overwriting the file.

8. Verify DNS

my-flask.lvh.me resolves to localhost by default. Add a hosts entry only for custom suffixes.

9. Start Devilbox

./dvl.sh up php httpd bind flask1

10. Open your browser

Visit http://my-flask.lvh.me or https://my-flask.lvh.me. The web server proxies the request to the Flask application on port 3000.

Next steps

• Keep requirements.txt pinned for reproducible local builds.
• Use a dedicated compose override per Python service when running multiple Flask apps.
• Configure HTTPS trust before testing browser integrations.