I'm interested in this detail because a few years back I was involved in a major big data project at a health insurance company and I cooked up a solution that involved ElasticSearch that was workable only to be shot down--it was political, but they had to do it with Kafka, full stop. The problem was, at that time, Kafka wasn't very mature and it wasn't a good solution for the problem, regardless. So our ES version got shelved.