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Deploy Python/Flask App ​

Install Python, pip and other necessary packages ​

Open the terminal for the root user, run the command to install Python venv, only run once if this is your first time Deploy Python/Flask App

bash
sudo apt install python3-venv -y

Create website ​

Let's say your python application runs on port 1406

Point the website DNS to the server and install SSL

Create virtual environment ​

Open the terminal for the site, run the command to set up a virtual environment and activate it:

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

Install application dependencies ​

If you have a requirements.txt file in the source code, use the command below, otherwise install the packages manually

bash
pip install -r requirements.txt

Use Gunicorn to deploy ​

Reasons to use gunicorn ​

Gunicorn (Green Unicorn) is a WSGI (Web Server Gateway Interface) HTTP server for Python applications. It is designed to serve Python web applications in production environments, providing better concurrency and load management than just using Flask's built-in server.

Install gunicorn ​

bash
pip install gunicorn

Test Your Application ​

Run your application to make sure it works:

bash
gunicorn --bind 0.0.0.0:1406 app:app

In the command gunicorn --bind 0.0.0.0:1406 app:app, the app:app part means:

  1. Application file name: The part before the colon (:) is the name of the Python file containing your Flask application. In this case, the Python file is app.py.
  2. Application object name: The part after the colon (:) is the name of the Flask application object in that Python file. In this case, the application object is app.

Combined, app:app tells Gunicorn that:

  • Find the app.py file.
  • In the app.py file, find the Flask object named app.

Gunicorn will:

  1. Open the app.py file.
  2. Find the Flask object defined as app.
  3. Run the Flask application using Gunicorn, listening on all IP addresses (0.0.0.0) on port 1406.

Set up Systemd service ​

Use the Systemd Service management feature to run gunicorn without having to hold a terminal.

Reference configuration is as follows:

ini
[Unit]
Description=domain.com web application
After=network.target

[Service]
User=flashvps
WorkingDirectory=/home/flashvps/domain.com
Environment="PATH=/home/flashvps/domain.com/venv/bin"
ExecStart=/home/flashvps/domain.com/venv/bin/gunicorn --workers 3 --bind 0.0.0.0:1406 app:app

[Install]
WantedBy=multi-user.target

WARNING

  1. You should change /home/flashvps/domain.com to the path to your respective website directory.

  2. --workers 3: This option specifies the number of worker processes Gunicorn will use. Here, it is configured to use 3 worker processes. Worker processes help Gunicorn handle multiple requests simultaneously, improving application performance.

  3. --bind 0.0.0.0:1406: This option specifies the IP address and port on which Gunicorn will listen. 0.0.0.0 means listen on all server IP addresses, and 1406 is the port that will be used. This allows the application to be accessible from any IP address on port 1406.

Your Python application will now be deployed and accessible through your server's IP address or domain.