I have recently analyzed Kafka as a message bus solution for our team. My take is that Kafka is a very mature and robust message system with clearly defined complexity and thus when used correctly, very dependable. The recent versions even have online rebalancing (but don't tell that to the Pulsar people). However "Kafka Streams" just make me shiver - I don't understand why someone would masquerade a project directly competing with other processing frameworks (e.g. Apache Flink or Spark) as being part of Kafka itself, when apart from utilizing Kafka's Producer and Consumer interfaces it really has nothing else in common with it. Streams is a giant, immature, complexity-hiding mess which as a responsible systems designer you have to run away from really, really fast.