Step 1: Update Your System

Before starting, ensure your Ubuntu system is up to date. Run the following commands to update your package list and upgrade any existing packages:

sudo apt update && sudo apt upgrade -y

Regular updates ensure that your server is secure and running smoothly, which is especially important for applications running on platforms like VPS Windows Servers.

Step 2: Install Python, Flask, and Virtual Environment

Install Python and the necessary tools for creating a virtual environment:

sudo apt install python3 python3-pip python3-venv -y

Next, create a project directory for your Flask app and navigate into it:

mkdir ~/myflaskapp
cd ~/myflaskapp

Create a Python virtual environment to keep your project dependencies isolated:

python3 -m venv venv

Activate the virtual environment:

source venv/bin/activate

Install Flask within the virtual environment:

pip install Flask

Step 3: Create a Simple Flask Application

Create a simple Flask app by creating a new Python file:

nano ~/myflaskapp/app.py

Add the following content to create a basic Flask app:

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello():
    return "Hello, World!"

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

Save and close the file.

Step 4: Install and Configure Gunicorn

Install Gunicorn inside your virtual environment:

pip install gunicorn

Now, run Gunicorn to serve your Flask application:

gunicorn --bind 0.0.0.0:8000 app:app

This will bind Gunicorn to port 8000 and run your Flask app. At this point, you can access your Flask app by navigating to http://your_server_ip:8000 in your browser.

Step 5: Set Up Gunicorn as a Systemd Service

To run Gunicorn as a background service, create a systemd service file:

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

Add the following content, replacing /home/your_username with the correct path to your Flask app:

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

[Service]
User=your_username
Group=www-data
WorkingDirectory=/home/your_username/myflaskapp
Environment="PATH=/home/your_username/myflaskapp/venv/bin"
ExecStart=/home/your_username/myflaskapp/venv/bin/gunicorn --workers 3 --bind unix:myflaskapp.sock -m 007 app:app

[Install]
WantedBy=multi-user.target

Save and close the file, then reload systemd to apply the new service:

sudo systemctl daemon-reload

Start the Gunicorn service and enable it to start at boot:

sudo systemctl start myflaskapp
sudo systemctl enable myflaskapp

Step 6: Install and Configure Nginx

Install Nginx with the following command:

sudo apt install nginx -y

Create an Nginx server block for your Flask app:

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

Add the following configuration:

server {
    listen 80;
    server_name your_domain_or_ip;

    location / {
        proxy_pass http://unix:/home/your_username/myflaskapp/myflaskapp.sock;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }

    location /static/ {
        alias /home/your_username/myflaskapp/static/;
    }
}

Enable the Nginx configuration and restart the service:

sudo ln -s /etc/nginx/sites-available/myflaskapp /etc/nginx/sites-enabled/
sudo systemctl restart nginx

Step 7: Obtain an SSL Certificate with Let's Encrypt (Optional)

To secure your Flask app with HTTPS, you can use Let's Encrypt to obtain a free SSL certificate. First, install Certbot:

sudo apt install certbot python3-certbot-nginx -y

Then, run Certbot to obtain and configure SSL:

sudo certbot --nginx -d your_domain

Follow the prompts to set up SSL. Certbot will automatically update your Nginx configuration.