title: Event Driven Architecture - backend services with two interfaces (interface types)
body: <p>Several articles about Event Driven Architectures recommend an <strong>event broker</strong> (for example Kafka via topics) to integrate backend services and in addition <strong>RESTful</strong> interfaces for these backend services (here an example from Guido Schmutz: Building event-driven (Micro)Services with Apache Kafka, 2019,  p. 19).</p>
  <p><a href="https://i.stack.imgur.com/wopu7.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/wopu7.png" alt="enter image description here" /></a></p>
  <p>The RESTful interfaces provide access for <strong>GUI</strong> and <strong>external services</strong>. These GUI and external services access the RESTful services via an <strong>API Gateway</strong>. So each backend service has two interface types: a RESTful interface and a channel interface (event broker).</p>
  <p>My question is: what are the advantages of providing RESTful API in addition / <strong>in parallel</strong> to the integration of backend services via an event broker? The reason for this question is that the event broker could provide the same capabilities (synchronous request response).</p>