Deploying a Flask App on Ubuntu 20.04 with Nginx and Gunicorn: A Step-by-Step Guide

1.  Updating the package index

sudo apt update

2.  Afterwards, installing the necessary packages to set up your Python environment is essential. These packages comprise python3-pip, a manager for Python packages, along with other crucial development tools for establishing a resilient programming environment. Execute the following commands to install python3, python3-pip, and Nginx:

sudo apt install python3-pip python3-dev nginx -y

3.  Now, proceed to install Flask and Gunicorn using the pip command:

pip3 install flask gunicorn

 4.  Creating a sample project and WSGI entry point

1. nano app.py

from flask import Flask
app = Flask(__name__)
@app.route('/')
def hello_world():
    return "Hey There! Welcome to Flask app!"
if __name__ == '__main__':
    app.run(debug=True,host='0.0.0.0')

2. nano wsgi.py

from app import app

if __name__ == "__main__":
    app.run()

You can assess Gunicorn's capability to host your project by executing the following command:

gunicorn --bind 0.0.0.0:5000 wsgi:app

Note: -  At this point, let's review the current organization of the folder structure:

myFlaskApp
  |____ app.py
  |____ wsgi.py
  |____ env

5.  Now, let's create a systemd service:

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

Next, paste the following contents into this file:

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

[Service]
User=raunak
Group=www-data
WorkingDirectory=/home/ubuntu/handsign  #Ensure you specify the correct project folder when entering the provided content:
ExecStart=gunicorn --workers 3 --bind unix:myproject.sock -m 007 wsgi:app

[Install]
WantedBy=multi-user.target

Activate this service by entering the following command:

sudo systemctl start app
sudo systemctl enable app

After activation, you'll notice that a file named app.sock is automatically generated. Let's take a look at the current folder structure:

myFlaskApp
  |____ app.py
  |____ wsgi.py
  |____ app.sock

6.  Now, let's proceed with configuring Nginx:

Create a file named app inside /etc/nginx/sites-available

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

Now, copy the following contents into this file:

server {
    listen 80;  # Listen on port 80 (HTTP)

    server_name 52.65.168.78;  # Replace with your domain or server IP

    location / {
        proxy_pass http://127.0.0.1:5000;  # Forward requests to port 5000
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
    }
}

Activate this configuration by running the following command:

sudo ln -s /etc/nginx/sites-available/app /etc/nginx/sites-enabled

7.  Afterwards, restart Nginx, and your website should be operational without any issues!

sudo systemctl restart nginx

8. If you are utilizing a firewall, such as ufw, remember to enable Nginx to receive incoming traffic on port 80:

sudo ufw allow 'Nginx Full'