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Exploring Ruby on Rails Engines

by Michael Blum on 16.07.2023

Among the many features of Ruby on Rails, Rails Engines stand out as an incredibly powerful tool. In this post, we will dive into Engines to understand their advantages and disadvantages, and we will discuss how they differ from Ruby Gems.

Understanding Rails Engines

Rails Engines can be considered mini-applications that provide functionality to their host applications. They are a way to package a specific Rails application or a set of functionalities that can be dropped into another Rails application. Engines have their own models, views, controllers, and routes, neatly packed in their own isolated namespace.

Advantages of Rails Engines

Disadvantages of Rails Engines

Rails Engines vs. Ruby Gems

While Rails Engines and Ruby Gems might seem similar in that they both allow you to extract and package reusable code, they are fundamentally different in terms of functionality and use-cases.

Ruby Gems are libraries that encapsulate Ruby code that can be utilized across different applications. These can include anything from small utility functions to complex libraries that handle tasks like authentication or data serialization. Gems cannot have views or controllers and aren’t meant to serve as standalone web applications. They provide a set of methods and classes that can be used within the context of an application.

On the other hand, Rails Engines are essentially small Rails applications that can be mounted within a Rails application. They come with all the capabilities of a fully-fledged Rails application, including models, views, controllers, routes, and even their own migrations. As such, they are much heavier than gems. They’re a good fit for encapsulating complex, standalone functionalities that have a web interface, like a commenting system, a forum, or a shopping cart.

In short: Engines are a higher level of abstraction, suitable for encapsulating entire application functionalities, including UI components. Conversely, gems are usually more focused on providing a specific set of functionalities without a user interface.


Rails Engines can significantly improve the maintainability and modularity of your applications.


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