Vert.x is an open source Eclipse toolkit used to build distributed and reactive systems that provides a flexible way to write applications that are lightweight and responsive through its implementations of Reactive Stream principles.

It is designed to be cloud-native: it allows many processes to run with very few resources (threads, CPU, and so on). In this way, Vert.x applications can use their CPU quotas more effectively in cloud environments. There is not unnecessary overhead caused by the creation of a great number of new threads.

It defines an asynchronous and non-blocking development model based on an event loop that handles requests, and avoids long waitings, on the client side, while the server side is stressed by a high number of invocations.

Since it's a toolkit and not a framework, Vert.x can be used as a typical third-party library, and you are free to choose the component needed for your target.

You can use Vert.x with multiple languages including Java, JavaScript, Groovy, Ruby, Ceylon, Scala, and Kotlin. In our example, we will use the Java language.