Gunicorn Deployment Guide for Flask Applications

How to deploy Flask application using Gunicorn?

Flask is a lightweight Python Web framework that is widely used to develop various types of Web applications. Gunicorn (Green Unicorn) is a Python-based HTTP server used to run WSGI (Web Server Gateway Interface) applications. This article will introduce how to use Gunicorn to deploy Flask applications, and attach specific code examples.

Step 1: Install dependencies

Before we start, we need to make sure that python and pip tools have been installed in the system. Open a terminal and execute the following command to install Flask and Gunicorn:

$ pip install flask gunicorn

Step 2: Create a Flask application

Create a file named app.py in the project directory Python file, select a simple sample application to demonstrate Gunicorn deployment. The following is a code example for a simple Flask application:

from flask import Flask

app = Flask(__name__)

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

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

The above code creates a Flask application named app and returns a simple Hello message on the root route.

Step 3: Test the Flask application

Execute the following command in the terminal to test whether the Flask application is running properly:

$ python app.py

If everything goes well, you should be able to See output similar to the following:

 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

Now, we have verified that the Flask application works properly.

Step 4: Use Gunicorn to start the application

Now we can use Gunicorn to start the Flask application. Execute the following command in the terminal:

$ gunicorn app:app

In the above command, app:app means that the application to be started is app# in the app.py file ##Object.

[2021-01-01 12:00:00 +0000] [12345] [INFO] Starting gunicorn 20.0.4
[2021-01-01 12:00:00 +0000] [12345] [INFO] Listening at: http://127.0.0.1:8000 (12345)
[2021-01-01 12:00:00 +0000] [12345] [INFO] Using worker: sync
[2021-01-01 12:00:00 +0000] [12345] [INFO] Booting worker with pid: 67890

http://127.0.0.1:8000/

Flask official documentation: https://flask.palletsprojects.com/
• Gunicorn official documentation: https://gunicorn.org/

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