Here are roughly the instructions that worked for me on Ubuntu 20.04 on 2022-04-10 (though I'm hand-waving a bit on prerequisites, I think I got it right though):
# Install prerequisites
sudo apt-get install apache2
sudo apt-get install libapache2-mod-wsgi-py3
sudo apt-get install python-dev-is-python3
sudo apt install certbot python3-certbot-apache
sudo pip install flask # some recommend virtualenv
# Download this repository
cd /var/www/html
sudo git clone https://github.com/shaunharker/minimalflaskexample
cd minimalflaskexample
# Fix the permissions so group is www-data with same
# privileges as user
bash ./permissions.sh
# Set up apache2
sudo ufw allow 'Apache Full'
sudo a2enmod ssl
sudo certbot --apache # and handle matters according to https://www.digitalocean.com/community/tutorials/how-to-secure-apache-with-let-s-encrypt-on-ubuntu-20-04
sudo a2enmod wsgi
sudo cp site.conf /etc/apache2/sites-available/site.conf
sudo emacs /etc/apache2/sites-available/site.conf # fix domain name with search and replace, adjust server alias, RTFM if confused ;)
sudo a2dissite 000-default
sudo a2ensite site
sudo systemctl restart apache2- https://python.plainenglish.io/how-to-securely-deploy-flask-with-apache-in-a-linux-server-environment-7eacd4c69a73
- https://www.codementor.io/@abhishake/minimal-apache-configuration-for-deploying-a-flask-app-ubuntu-18-04-phu50a7ft
- https://flask.palletsprojects.com/en/2.1.x/quickstart/
- https://www.digitalocean.com/community/tutorials/how-to-secure-apache-with-let-s-encrypt-on-ubuntu-20-04
- https://www.digitalocean.com/community/tutorials/how-to-install-the-apache-web-server-on-ubuntu-20-04#step-5-%E2%80%94-setting-up-virtual-hosts-(recommended)
- https://stackoverflow.com/questions/28207761/where-does-flask-look-for-image-files
- https://stackoverflow.com/questions/23327293/flask-raises-templatenotfound-error-even-though-template-file-exists