Now that dust has settled after Youtube Thumbnail Downloader tutorial, it’s time for a new thing. When you run a Flask developement server, it tells you that it isn’t suited for prodution:

WARNING: This is a developlment server. Do not use it in a production deployment.

Fair point. It hasn’t been tested for security and whatnot. There are a few alternatives, most notably Nginx and Apache. I go for the latter. I assume that you have Ubuntu server up and running. I won’t actually cover developing a Flask application. I will use a simple example that only demonstrates WSGI configuration. I think that the whole process is straightforward. Let’s go!

Installing libraries

We start with installing required packages. First, make sure your system is up to date:

sudo apt update && upgrade

We are going to need some packages on our system, most notably Apache and Python. Issue the following command to install them:

sudo apt-get install apache2 libapache2-mod-wsgi-py3 python3 python3-pip python3-venv git curl

Not too much of a sweat, isn’t it?

Cloning sources

Change directory to home:

cd ~

Then clone the repository:

https://github.com/izdwuut/flask-wsgi && cd flask-wsgi

It’s a pretty standard Flask app that utilizes app factory pattern. The only file worth mentioning is wsgi.py. It tells the server how to run our app. Let’s take a closer look:

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from app import create_app

application = create_app()

3. This is all we have to do - create our application instance using create_app imported from app module.

Adding virtual environment

Before we proceed, we need to create a Python virtual environment. While in flask-wsgi directory, issue the following command to install and activate venv:

python3 -m venv venv && source venv/bin/activate

Now we can install our requirements:

pip3 install -r requirements.txt

Hosting the files

To host our app, we need to copy our sources to /var/www directory. Run the following command:

sudo cp . /var/www/flask-wsgi -r

To actually run the app, Apache must be configured first.

Running Apache and adding a site

The following command will start Apache. You will be prompted for your user’s password:

systemctl start apache2

Apache utilizes a concept of sites. They are config files for your… well, sites. They contain all the data about your website (or a Flask app in our case), from directory on server to port which Apache listens on. They reside in /etc/apache2/sites-available. Let’s create our site:

sudo touch /etc/apache2/sites-available/flask-wsgi.conf

Put the following lines in it:

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Listen 5000
<VirtualHost *:5000>
	ServerName 127.0.0.1
	WSGIScriptAlias / /var/www/flask-wsgi/wsgi.py
	WSGIDaemonProcess flask-wsgi python-path=/var/www/flask-wsgi/venv/lib/python3.6/site-packages:/var/www/flask-wsgi
	WSGIProcessGroup flask-wsgi
	<Directory /var/www/flask-wsgi/app/>
		Order allow,deny
		Allow from all
	</Directory>
	ErrorLog ${APACHE_LOG_DIR}/error.log
	LogLevel warn
	CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>

1. Tells the Apache to listen on port 5000. You are free to change it to any value you want, just remember to also change it in line 2.

3. Your server name. In our case it’s localhost loopback address.

4. The first argument tells apache to serve your app at /, and the second tells where the WSGI config is located at.

5. Here we spawn a process named flask-wsgi and add two values to Python path separated by a colon:

• /var/www/flask-wsgi/venv/lib/python3.6/site-packages - location of site packages in virtual environment. Change the python3.6 bit if you use different version of Python.
• /var/www/flask-wsgi - location of our script on server

6. Create process group flask-wsgi.

7. Set application directory. Note that it points to app directory.

9. Allow all connections.

11-13. Add logging. ${APACHE_LOG_DIR} stands for /var/log/apache2.

Having that, we can activate the site:

sudo a2ensite flask-wsgi.conf && sudo service apache2 reload

Testing the application

The application should be up and running. Check it using curl:

curl 127.0.0.1:5000

This is the output you should get:

Hello world!

And that’s it. Thanks for your attention!