When we say that a system or an application is responsive, it means that the application or system responds quickly to all users in a given time in all conditions, and that is in good condition as well as bad. It ensures a consistent positive user experience.

Responsiveness is required for a system for usability and utility. A responsive system means that up on system failure, either because of an external system or a spike in traffic, the failures are detected quickly, and dealt with effectively in a short time without the users knowing of the failure. An end user must be able to interact with the system by providing rapid and consistent response times. A user must not face any failure during interaction with the system, and it must deliver a consistent quality of service to the user. That consistent behavior solves the failures and builds end-user confidence in the system. Quickness and a positive user experience under various conditions make a system responsive. It depends on the two other traits of a reactive application or system, that is, resilience and scalability. Another trait, that is, event-driven or message-driven architecture, provides the overall foundation for a responsive system. The following diagram illustrates a responsive system:

As you can see in the preceding diagram, a responsive system depends on resilient and scalability of the system, and these depend on its event-driven architecture. Let's look at the other traits of a reactive application.