Web Server Gateway Interface

Describing a WSGI Server

• A web server gateway interface (WSGI) is a server specification programmed in Python
• Specifically, a WSGI server is used to forward requests from a web server to a web application in Python
• The web server can be an Apache or Nginx web server
• The backend web application can be Flask, Django, etc.
• By doing this, we can free up the web server from serving dynamic content using heavyweight Python threads
• In other words, a WSGI server is used for serving clients with files containing dynamic business logic
• A WSGI framework is used for creating web applications

Describing the Functions of a WSGI Server

• Gunicorn is a popular WSGI server

• Gunicorn provides the following functions:

  • Control the number of worker threads for handling requests
  • Control the maximum number of simultaneous clients
  • Control the maximum number of pending connections
  • Limit the allowed size of an HTTP request header field
  • Control the maximum number of requests a worker will process before restarting
• The above functions are only a few of the many capabilities of Gunicorn

Responsibilities between a Web and WSGI Server

• Three common building blocks when deploying a Python web application to production are the following:

  • A web server (like nginx)
  • A WSGI application server (like Gunicorn)
  • Our actual application (written using Django or Flask)

• The web server does the following:

  • Accepts requests
  • Handles general domain logic
  • Handles HTTP connections

• A WSGI server does the following:

  • Only handles requests meant for an application
• The application server only cares about requests meant for the application it is associated with

• By doing this, we can achieve the following:

  • Communicate with a single web server
  • Remove some of the web server's load
  • Only run one process for a web application
• In other words, Gunicorn takes care of everything happening between the web server and an application

A WSGI Server as an Application Server

• Specifically, a WSGI server acts as an application server
• An application server serves clients with files with business logic
• Typically, this content containing business logic is dynamic
• Specifically, the application server is responsible for running code that transforms data to provide a specialized functionality
• Communication between the application server and its client doesn’t need to take the form of HTTP messages

Describing WSGI Frameworks

• As stated previously, a WSGI framework is used for creating web applications
• The most popular WSGI frameworks are flask and django

• However, most frameworks support the following functions:

  • URL routing
  • Receiving requests
  • Sending responses
  • Using template engines
• Requests are typically in the form of request objects
• Responses take the form of response objects
• These objects contain the information received from and sent to a user's browser
• URL routing involves matching an incoming HTTP request to a particular piece of Python code to be invoked
• Template engines represent dynamic behavior associated with HTML output
• These template engines are obviously represented using Python code

References

• Describing a Gunicorn Pipeline with Nginx
• Why use a WSGI Server?
• Basics of a WSGI Server
• Setting Up a WSGI and Web Server
• Functions of a WSGI Server
• PEP 333: WSGI as a Python Standard
• Differentiating between WSGI Framework and WSGI Server
• Another Basic Description of WSGI
• Describing Configurations in Gunicorn
• Functions of a WSGI Framework