Is Unicorn a Web Server?


Angela Bailey

Is Unicorn a Web Server?

If you are new to web development, you may have come across the term “Unicorn” and wondered if it is related to web servers. In this article, we will explore what Unicorn is and its role in the world of web development.

What is a Web Server?

A web server is a computer program that serves as the backbone of websites. It receives requests from clients (usually web browsers) and responds by delivering the requested web pages or other resources. Common examples of web servers include Apache, NGINX, and Microsoft IIS.

Introduction to Unicorn

Unicorn is not a web server but rather a Ruby application server designed specifically for Rack-based applications. Rack is a popular interface in Ruby for building web applications. Unicorn helps in serving these Rack-based applications efficiently.

Why Use Unicorn?

  • Stability: Unicorn is known for its stability, making it an excellent choice for production environments.
  • Performance: It utilizes multiple processes to handle requests concurrently, resulting in improved performance.
  • Worker Model: Unlike some other servers that use threads or processes per request, Unicorn follows a worker model where multiple worker processes share the load.
  • Zero Downtime Deployment: With Unicorn’s rolling restart feature, you can deploy updates without disrupting ongoing requests.

Configuration and Usage

To use Unicorn as your application server, you need to configure it within your Ruby project. Typically, this involves creating a configuration file where you specify the application’s location, the number of worker processes, and other settings.

Once configured, you can start Unicorn by running a command like:

$ unicorn -c config/unicorn.rb

After starting Unicorn, it will listen on a specified port (often port 8080) and serve your Rack-based application.

Alternatives to Unicorn

While Unicorn is a well-respected choice for serving Rack-based applications, there are other alternatives available:

  • Puma: Puma is another popular Ruby application server known for its speed and concurrency capabilities.
  • Passenger: Passenger is an application server that supports multiple languages, including Ruby. It offers ease of use and excellent integration with web servers like Apache and NGINX.


In summary, Unicorn is not a web server but a Ruby application server specifically designed for Rack-based applications. It offers stability, performance, and zero downtime deployment. While Unicorn is an excellent choice for serving Rack-based apps, alternatives like Puma and Passenger also exist.

If you’re developing Ruby web applications using Rack, give Unicorn a try and see if it meets your needs!

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