NGINX Flask server

Introduction

This is a tutorial on how to set up a Flask server with NGINX.

Let us denote an App. This App is a Flask application that we want to serve with NGINX. The App is located in the directory /home/user/app.

from flask import Flask
app = Flask(__name__)

@app.route("/")
def hello():
    return "<h1 style='color:blue'>Hello There!</h1>"

if __name__ == "__main__":
    app.run(host='0.0.0.0')

The App is running on port 5000. We want to serve this App with NGINX on port 80.

Sometimes Linux distros come with a firewall. We need to open port 80 for NGINX to work and 5000 for the App to work.

sudo ufw allow 80
sudo ufw allow 5000

You may visit the App at http://localhost:5000

Installing Gunicorn

Gunicorn is a Python WSGI HTTP Server for UNIX. It is a pre-fork worker model. The Gunicorn server is broadly compatible with various web frameworks, simply implemented, light on server resources, and fairly speedy.

pip install gunicorn

Running the app with Gunicorn

gunicorn --bind 0.0.0.0:5000 app:app

Now that we have Gunicorn installed, we can run the App with Gunicorn. We can visit the App at http://localhost:5000

Setting up a systemd service

We can set up a systemd service to run the App with Gunicorn. This will allow us to run the App as a service.

sudo nano /etc/systemd/system/app.service

[Unit]
Description=Gunicorn instance to serve app
After=network.target

[Service]
User=user
Group=www-data
WorkingDirectory=/home/user/app
Environment="PATH=/home/user/app/venv/bin"
ExecStart=gunicorn --workers 3 --bind localhost:5000 app:app

[Install]
WantedBy=multi-user.target

Starting the service

You can start the service with the following command.

sudo systemctl start app

Enabling the service

You can enable the service with the following command. This will start the service on boot.

sudo systemctl enable app

Checking the status of the service

You can check the status of the service with the following command.

sudo systemctl status app

Stopping the service

sudo systemctl stop app

Installing NGINX

To install NGINX, run the following command.

sudo apt install nginx

Configuring NGINX

Using the nano editor, open the file /etc/nginx/sites-available/default

sudo nano /etc/nginx/sites-available/default

With nano editor, press Ctrl + W and type server_name. This will take you to the line server_name _;. Replace _ with localhost. This will allow you to visit the App at http://localhost

server {
    listen 80;
    server_name localhost;

    location / {    
        proxy_pass http://localhost:5000;
    }
}

Restarting NGINX

sudo systemctl restart nginx

Checking the status of NGINX

sudo systemctl status nginx

Checking the NGINX configuration

sudo nginx -t

Now that we have NGINX installed and configured, we can visit the App at http://localhost

What is missing is the SSL certificate. We can use Let's Encrypt to get a free SSL certificate.

Installing Certbot

sudo apt install certbot python3-certbot-nginx

Getting the SSL certificate for the domain example.com

sudo certbot --nginx -d example.com -d www.example.com

Renewing the SSL certificate

sudo certbot renew --dry-run

Checking the status of the SSL certificate

sudo certbot certificates

Checking the SSL certificate expiration date

sudo certbot certificates | grep Expiry

Checking the SSL certificate renewal date

sudo certbot certificates | grep Renew

But now we have an issue the certificate will expire in 90 days. We need to renew the certificate every 90 days. We can automate this process with a cron job.

Setting up a cron job

sudo crontab -e

0 0 1 * * sudo certbot renew

This will run the command sudo certbot renew every first day of the month at midnight.

Conclusion

We have set up a Flask server with NGINX. We have also set up a cron job to renew the SSL certificate every 90 days. This will allow you to run your website on a cloud server for free or even a local server.