This thesis evaluates the performance of a core-banking application that consumes messages from a Kafka topic, and after performing validation and a static transformation stores the results in another Kafka topic. Performances are evaluated on two different versions of the application: traditional and reactive. The focus is on the way the two applications interact with Kafka. Both versions are developed using Spring: the traditional version uses Spring MVC while the reactive one uses Spring WebFlux. Spring WebFlux internally uses Project Reactor. Both versions consume and produce messages from/to Apache Kafka, however in the reactive version messages are consumed and produced using functional APIs provided by Reactor Kafka.