What is Gunicorn? WHAT DOES IT DO?

The standard web servers such as Apache, and NGINX don’t know how to communicate with your Python applications. Web servers receive the request from a client(Web browser) and return a response. The web server doesn’t create the response, it only returns the response. So, a server needs to talk with a Web Application that can create a response.

And what Web Applications can do? Anything your project needs to do. I am sure you all have cool ideas to release to the world. We almost live on the web these days. So, what you build will need to communicate to the web servers in order to reach your users/audience over the internet. Therefore, we need an architecture, sort of a protocol, everyone agrees on, to bridge the request-response cycle between your web server and web application.

WISGI

WSGI comes into the picture because it basically provides that bridge of your need to communicate between your Web Server and Web Application. WSGI (Web Server Gateway Interface), is a set of rules which allow a WSGI-compliant server to work with a WSGI-compliant Python application. WSGI also handles scaling for web servers to be able to handle thousands of requests so you don’t have to think about accepting multiple requests at a time.

Gunicorn is one implementation of a WSGI server for Python applications.

Gunicorn is a WSGI-compliant web server for Python Applications that receive requests sent to the Web Server from a Client and forwards them to the Python applications or Web Frameworks (such as Flask or Django) in order to run the appropriate application code for the request.

Within the applications code, you need to create the callable function that will be the Gunicorn entry point into the application, so for example, you might define a wsgi.py file with the following code:

def app(environ, start_response):
    path = environ.get('PATH_INFO')
    if path == '/':
        response_body = "Home Page"
    else:
        response_body = "A new page"
    status = "200 OK"
    response_headers = [("Content-Length", str(len(response_body)))]
    start_response(status, response_headers)    return [response_body]

Later, you should start your Gunicorn workers.

gunicorn --bind 127.0.0.1:8000 --workers=4 wsgi:app

Now, you can access your web app at 127.0.0.1:8000.