As web applications grow, they often need to handle long-running tasks without slowing down user interactions. Sidekiq is a popular choice among Ruby on Rails developers for processing background jobs efficiently. This guide will cover what Sidekiq is, how to set it up in a Rails application, and provide practical examples to illustrate its usage.

Web browsers have a set of rules in place to prevent web pages from accessing resources on different origins without permission. This policy, known as the same-origin policy, ensures that a web page can only access resources that have the same origin as the page itself. However, there are scenarios where web applications need to communicate with other origins for legitimate purposes, such as fetching data from an API or loading web fonts. In such cases, cross-origin resource sharing (CORS) comes into play. In this article, we will explore how to implement CORS in a Rails application and understand its significance.