Introduction

The first two chapters were focused on how to build a Kafka cluster, run a producer, and run a consumer. Now that we have a producer of events, we will process those events.

In a nutshell, event processing takes one or more events from an event stream and applies actions to those events. In general, an enterprise service bus has commodity services, the most common services are the following:

• Event handling
• Data transformation
• Data mapping
• Protocol conversion

The operation of processing events involves the following:

• An event stream to filter some events from the stream
• Event validation against an event schema
• Event enrichment with additional data
• Event composition (aggregation) to produce a new event from two or more events 

This chapter is about message validation, the following chapters will be about enrichment and composition.

Before going into a concrete recipe, let's present a case study. Imagine that we are modeling the systems of Doubloon, a fictional company dedicated to cryptocurrency...