Flask Hello World App with Apache WSGI from scratch

 

Flask Hello World App with Apache WSGI

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Note

Flask is a fantastic micro web framework for Python, however, it is not a native web language. So to get our Python code running on a web server is tricky.

Apache will use WSGI file to access our Flask application, so the WSGI file allows Apache to interact with Python as if it is native. It's a simple script.

In this article, we'll start from a very simple app which just outputs "Hello, Flask!"

First, we just run it with Python interpreter. Then, we'll serve the page via Apache with WSGI.

Install and Enable mod_wsgi

WSGI (Web Server Gateway Interface) is an interface between web servers and web apps for python.

mod_wsgi is an Apache HTTP server module that enables Apache to serve Flask applications.

We need to use the following command to install mod_wsgi:

$ sudo apt-get install libapache2-mod-wsgi python-dev

To enable mod_wsgi, we can use the following command:

$ sudo a2enmod wsgi 

Files

THe picture below shows our application files:

The __init__.py looks like this:

from flask import Flask
app = Flask(__name__)
@app.route("/")
def hello():
    return "Hello, Flask!"
if __name__ == "__main__":
    app.run()

We can directly execute an app via app.run() since Flask(more specifically, Werkzeug) has an internal WSGI server for test.

Virtualenv

Setup virtualenv:

$ sudo virtualenv venv
$ source venv/bin/activate
(venv)$ 

Install Flask

Install Flask:

(venv)$ sudo pip install Flask

Run server

Install Flask:

(venv)$ $ sudo python __init__.py 
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

This tells us the web server has been started and if we point our browser now to localhost:5000/ we will see the hello function is executed and the browser will display the text "Hello, Flask!"

Apache setup - WSGI

Now we want to serve the page using Apache via WSGI which halps to get our code deployed on Apache.

Here is the Apache config file (/etc/apache2/sites-available/flaskhelloworldsite.com.conf):

<VirtualHost *:80>
    ServerAdmin webmaster@flaskhelloworldsite.com
    ServerName www.flaskhelloworldsite.com
    ServerAlias flaskhelloworldsite.com
    ErrorLog /var/www/flaskhelloworldsite.com/logs/error.log
    CustomLog /var/www/flaskhelloworldsite.com/logs/access.log combined

    WSGIDaemonProcess helloworldapp user=www-data group=www-data threads=5
    WSGIProcessGroup helloworldapp
    WSGIScriptAlias / /var/www/FLASKAPPS/helloworldapp/helloworldapp.wsgi
    Alias /static/ /var/www/FLASKAPPS/helloworldapp/static
    <Directory /var/www/FLASKAPPS/helloworldapp/static>
        Order allow,deny
        Allow from all
    </Directory>

</VirtualHost>

$ sudo a2ensite flaskhelloworldsite.com.conf

The WSGI file (/var/www/FLASKAPPS/helloworldapp/helloworldapp.wsgi):

#!/usr/bin/python
import sys
sys.path.insert(0,"/var/www/FLASKAPPS/")
from helloworldapp import app as application

Add the following line to /etc/hosts file:

127.0.0.1 flaskhelloworldsite.com

Also, we need to create /var/www/flaskhelloworldsite.com/logs directory:

$ sudo mkdir -p /var/www/flaskhelloworldsite.com/logs

Change the owner:

$ sudo chown -R www-data:www-data flaskhelloworldsite.com

Reload Apache

Let's reload the Apache server:

$ sudo /etc/init.d/apache2 reload

Go to the browser and type in flaskhelloworldsite.com:

 

 

More questions please refer - https://stackoverflow.com/

 

references - https://www.bogotobogo.com/