Is Puma a Web Server or an App Server?


Angela Bailey

Is Puma a Web Server or an App Server?

When it comes to developing web applications, understanding the different components and technologies involved is essential. One question that often arises is whether Puma is a web server or an app server. In this article, we will explore the capabilities of Puma and clarify its role in the web application ecosystem.

The Basics: Web Servers vs. App Servers

Before diving into Puma, let’s briefly distinguish between web servers and app servers. A web server is responsible for handling HTTP requests from clients (like browsers) and returning the appropriate responses. It primarily serves static files such as HTML, CSS, JavaScript, images, etc.

App servers, on the other hand, are designed to execute dynamic code and generate dynamic content. They can process complex business logic and interact with databases or other external systems.

Puma: The Hybrid Solution

Puma is a high-performance app server. It is built on top of the Ruby language and provides multi-threading capabilities that enhance concurrency in web applications. However, it also includes a basic web server functionality to handle initial requests.

When you start a Ruby-based web application with Puma, it creates multiple worker processes that can handle concurrent requests simultaneously. Each worker process can spawn multiple threads to handle even more parallelism within each worker process.

Puma as an App Server

Puma’s primary role is to execute your Ruby code within each worker process. It can load your application framework (like Ruby on Rails) and handle incoming HTTP requests by routing them to the appropriate controller actions.

  • Concurrent Execution: Puma’s multi-threading capabilities allow it to handle multiple requests concurrently, making it suitable for high-traffic applications.
  • Scalability: By utilizing multiple worker processes, Puma can scale your application across multiple CPU cores.
  • Connection Management: Puma manages connections efficiently, which is crucial for handling a large number of simultaneous requests.

Puma as a Web Server

Puma also includes a basic web server functionality that can serve static files and handle initial HTTP requests. However, its web server capabilities are limited compared to dedicated web servers like Nginx or Apache.

  • Development Convenience: Puma’s built-in web server allows you to quickly test your application during development without the need for additional software installations.
  • Simplicity: For small-scale applications or development purposes, using Puma as both the app server and web server can simplify the setup process.


In summary, Puma is primarily an app server designed to execute Ruby code and handle dynamic content generation within web applications. However, it also includes a basic web server functionality suitable for development or small-scale deployments.

The hybrid nature of Puma makes it a powerful choice for Ruby-based web applications that require concurrent execution and scalability. By leveraging its multi-threading capabilities, you can improve the performance and responsiveness of your application even under high loads.

Understanding the role of Puma in your application stack will help you make informed decisions when choosing the appropriate components for your specific use case. Whether you use it solely as an app server or take advantage of its built-in web server capabilities, Puma offers flexibility and performance for your Ruby web applications.

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