Heroku is a platform, that is, an environment that provides you with the foundation to run your applications without worrying about the nitty-gritty of how it all works under the hood. You build an application, push it to Heroku, and voila, the slug compiler builds your source into an executable and ready-to-run application. What's more, it also creates a URL for the application to use. While all this magic works for you in no time, there is a robust, highly available, scalable, and failure-proof foundation underneath that makes all this possible. The core element of the Heroku platform is the Heroku stack—a combination of the operating system, language runtime, and associated libraries that provide a complete execution environment for users to run applications of varying workloads and scale seamlessly.

In the deployment stack, the operating system defines the base technology used by the Heroku platform, and it has varied across various releases of the Heroku stack...