Python/Flask
Flask
Installation
## Linux / macOS mkdir myproject cd myproject # python3 -m venv .flask python3 -m venv .venv . .venv/bin/activate
## Windows mkdir myproject cd myproject py -3 -m venv .venv .venv\Scripts\activate
## Next Common Step # pip install Flask pip3 install Flask
# End deactivate
References:
Quick Start
Flask Hello World
helloworld.py
from flask import Flask
app = Flask(__name__)
@app.route("/")
def hello_world():
return "<p>Hello, World!</p>\n"
Run the server:
flask --app helloworld run
NOTE: As a shortcut, if the file is named app.py or wsgi.py, you don’t have to use --app. See Command Line Interface for more details.
- Meaning, just simply rename helloworld.py to app.py (or wsgi.py) and you can simply run run:
flask run
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
Note:
* Running on http://127.0.0.1:5000
Test the server:
curl http://127.0.0.1:5000 <p>Hello, World!</p>
References:
Hello World Headers
$ curl -i http://127.0.0.1:5000 HTTP/1.1 200 OK Server: Werkzeug/3.1.4 Python/3.12.3 Date: Sat, 13 Dec 2025 22:05:42 GMT Content-Type: text/html; charset=utf-8 Content-Length: 20 Connection: close <p>Hello, World!</p>
WSGI
Apache mod_wsgi-express
$ cd hello-app $ python -m venv .venv $ . .venv/bin/activate $ pip install . # install your application $ pip install mod_wsgi
wsgi.py : (or yourapp.wsgi)
## IIMPORT PATTERN from hello import app application = app ## OR ## FACTORY PATTERN from hello import create_app application = create_app()
Configure mod_wsgi-express and specify the number of worker processes:
mod_wsgi-express start-server wsgi.py --processes 4
Example running mod_wsgi-express as root, to bind to port 80/443, but then drop permissions and binding app as different user:
sudo /home/hello/.venv/bin/mod_wsgi-express start-server /home/hello/wsgi.py \ --user hello --group hello --port 80 --processes 4
Reference: https://flask.palletsprojects.com/en/stable/deploying/mod_wsgi/
Apache mod_wsgi and WSGIScriptAlias
Another WSGI option using mod_wsgi and WSGIScriptAlias
/path/to/your/yourapp.wsgi : ( the "bridge" between apache and Flask )
import sys
import os
# Add your project directory to Python's path
project_home = os.path.dirname(os.path.abspath(__file__))
if project_home not in sys.path:
sys.path.insert(0, project_home)
# Import the 'app' object from your Flask application file (e.g., app.py)
from app import app as application
Virtual Host :
<VirtualHost *:80>
ServerName yourdomain.com
# Points to your WSGI script
WSGIScriptAlias / /path/to/your/yourapp.wsgi
# Configure daemon processes
WSGIDaemonProcess yourapp_daemon user=www-data group=www-data threads=5
WSGIProcessGroup yourapp_daemon
# Grant access to the application directory
<Directory /path/to/your/project/folder>
WSGIProcessGroup yourapp_daemon
WSGIApplicationGroup %{GLOBAL}
Order deny,allow
Allow from all
Require all granted
</Directory>
ErrorLog /var/log/apache2/yourdomain.com_error.log
CustomLog /var/log/apache2/yourdomain.com_access.log combined
</VirtualHost>
Enable the virtual host:
# On Ubuntu/Debian sudo a2ensite yourdomain.com.conf sudo systemctl restart apache2 # On Fedora/RHEL sudo systemctl restart httpd
Prerequisites
- Python Virtual Environment: Your Flask application should be installed in a dedicated Python virtual environment for dependency isolation.
- Apache Web Server: Apache must be installed and running.
- mod_wsgi: The mod_wsgi package must be installed and enabled for the correct Python version (e.g., libapache2-mod-wsgi-py3 on Ubuntu systems).
- No app.run(): Ensure that any app.run() calls are removed or placed inside an if __name__ == '__main__': block in your Flask app's main file, as Apache will manage the server lifecycle.
Reverse Proxy
Tell Flask it is being reverse Proxied:
from werkzeug.middleware.proxy_fix import ProxyFix
app.wsgi_app = ProxyFix(
app.wsgi_app, x_for=1, x_proto=1, x_host=1, x_prefix=1
)
reference: https://flask.palletsprojects.com/en/stable/deploying/proxy_fix/
Apapache Configuration:
LoadModule proxy_module modules/mod_proxy.so LoadModule proxy_http_module modules/mod_proxy_http.so ProxyPass / http://127.0.0.1:8000/ RequestHeader set X-Forwarded-Proto http RequestHeader set X-Forwarded-Prefix /
reference: https://flask.palletsprojects.com/en/stable/deploying/apache-httpd/
Systemd Flask Service
/etc/systemd/system/myproject.service
[Unit] Description=Gunicorn instance to serve myproject After=network.target [Service] User=youruser WorkingDirectory=/path/to/your/project Environment="FLASK_ENV=production" ExecStart=/path/to/your/project/venv/bin/gunicorn -w 4 'app:app' -b 0.0.0.0:8000 Restart=always [Install] WantedBy=multi-user.target
sudo systemctl daemon-reload sudo systemctl start myproject sudo systemctl enable myproject
Check logs with:
sudo systemctl status myproject journalctl -u myproject