[allengeorge]

So can a RDBMS... But that doesn't mean that Kafka and databases are related.

As multiple comments have stated above, Kafka is really a distributed message subsystem. Its core interface is a set of topics that one can publish to, and that consumers can read from (in other words, a pub-sub system). Kafka doesn't inspect the message payload at all.

Elasticsearch is a unstructured (to some extent) document store that's optimized around document search. So at the very least, the payload is important when using Elasticsearch.