What Web Server Is Flask?


Heather Bennett

Flask is a micro web framework written in Python. It is lightweight and designed to be easy to use, making it a popular choice for building web applications.

But have you ever wondered what exactly happens when you run a Flask application? In this article, we will explore the role of Flask as a web server.

What is a web server?

In simple terms, a web server is a software that handles HTTP requests and serves HTML pages or other resources in response. It acts as an intermediary between the client (usually a web browser) and the application or website being accessed.

Flask as a development server

When you start developing a Flask application, it comes with its own built-in development server. This server is designed to be used during the development process and should not be used in production environments.

The development server provided by Flask is lightweight and convenient. It automatically reloads the application whenever changes are made to the code, making it easy to test and debug your application without manually restarting the server.

Running Flask on production

While Flask’s built-in development server is great for testing and debugging, it is not suitable for handling production traffic. When deploying your Flask application for production use, you will need to use a more robust web server.

There are several popular web servers that can be used to run Flask applications in production, such as Apache HTTP Server, Nginx, or Gunicorn. These servers are specifically designed to handle high traffic loads efficiently and securely.

Apache HTTP Server

Apache HTTP Server is one of the most widely used web servers in the world. It offers excellent performance and stability while providing extensive configuration options.

To run your Flask application using Apache HTTP Server, you can use mod_wsgi module. This module allows Apache to interface with WSGI (Web Server Gateway Interface), which is the standard interface between web servers and web applications in the Python ecosystem.


Nginx is a lightweight and high-performance web server that is known for its ability to handle concurrent connections efficiently. It is often used as a reverse proxy server, which means it can forward requests to multiple backend servers, including Flask applications.

To run your Flask application using Nginx, you can configure Nginx as a reverse proxy server and set up a separate Flask application server using any WSGI-compatible server, such as Gunicorn or uWSGI.


Gunicorn (short for Green Unicorn) is a Python WSGI HTTP server. It is designed to be simple, reliable, and scalable. Gunicorn can be used as a standalone web server or as an interface between Nginx and your Flask application.

To run your Flask application using Gunicorn, you need to install Gunicorn separately and start it with the appropriate configuration options. Gunicorn will then listen for incoming requests and forward them to your Flask application for processing.


Flask itself provides a built-in development server for convenience during the development process. However, when deploying your Flask application for production use, it is important to choose a suitable web server that can handle high traffic loads efficiently and securely.

Apache HTTP Server, Nginx, and Gunicorn are all popular choices for running Flask applications in production. Each has its own strengths and configuration options, so it’s important to consider your specific requirements when choosing the right web server for your Flask application.

By understanding the role of Flask as a web server and choosing the appropriate setup for deployment, you can ensure that your Flask application runs smoothly and efficiently in production environments.

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