This article explains how to deploy a simple Flask application sandboxed with a
virtualenv and served by Apache HTTP server using the
mod_wsgi module. For newcomers, Flask is a lightweight web application framework written in Python. Sometimes classified as a microframework, Flask provides a lightweight codebase that can be easily extended to become an API, a simple web app, or a complex eCommerce platform.
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Install Apache server
$ sudo yum install httpd $ $ # by default the server is down. $ sudo systemctl start httpd
$ sudo yum install mod_wsgi $ $ # restart apache $ sudo systemctl restart httpd
$ sudo httpd -M | grep wsgi wsgi_module (shared) # <-- the OK response
Virtual environments will sandbox the app to run isolated from the global server environment
$ sudo pip install virtualenv
Code the Flask App
We will use a simple Flask application that serves a simple
Hello World message for all routes.
As mentioned before, this setup is executed on CentOs. The steps are:
/var/www - the www_root of Apache server, and create the project directory.
$ cd /var/www $ mkdir hitme
To have a runnable Flask app, we need to create two files:
app.py inside the app folder. The files are structured as below:
/var/www/hitme | - run.py | - app/__init__.py
run.py is responsible to bootstrap the Flask app defined in the
app/init.py file contents
from flask import Flask app = Flask(__name__) @app.route("/") def hello(): return "Hello world!"
run.py file contents
import os from app import app #---------------------------------------- # launch #---------------------------------------- if __name__ == "__main__": port = int(os.environ.get("PORT", 5000)) app.run(host='0.0.0.0', port=port, debug=True)
We have the test application, now let's start it to see something on the screen. First, we need to create and activate the virtual environment.
$ cd /var/www $ virtualenv --python=python3 hitme # the venv is created inside the app folder $ cd /var/www/hitme $ source bin/activate
At this point, we will run the next commands inside the
VENV. Let's install Flask
$ pip install flask
To run, a Flask application require
FLASK_APP environment variable.
$ export FLASK_APP=run.py # please notice the name $ flask run # start the app $ # our app is running on port 5000
To execute a Flask application under the Apache HTTP server we need to bridge our application to the Apache engine using the mod_wsgi module. For this we need to create a new file
wsgi.py inside our project folder:
/var/www/hitme | - wsgi.py | - run.py | - app/__init__.py
wsgi.py file contents
#!/usr/bin/env python import sys import site site.addsitedir('/var/www/hitme/lib/python3.6/site-packages') sys.path.insert(0, '/var/www/hitme') from app import app as application
The next step is to configure Apache to serve the app and use this
wsgi loader. The following settings should be added to the
httpd.conf. On CentOS the file location is
<VirtualHost *:80> ServerName localhost WSGIDaemonProcess hitme user=apache group=apache threads=2 WSGIScriptAlias / /var/www/hitme/wsgi.py <Directory /var/www/hitme> Require all granted </Directory> </VirtualHost>
Close and save the file and restart Apache to load the new settings.
$ # restart apache $ sudo systemctl restart httpd
Our Flask app should be served by the Apache HTTP server. We can test the deploy by using
$ lynx localhost # lynx
- How To Serve Flask Applications
- Minimal Apache configuration for Flask
- Run Python as a Web Application on CentOS
Thank you! Btw, my (nick) name is Sm0ke and I'm pretty active also on Twitter.