AWS used ElasticSearch; but it was a big headache for Elastic the company to support because it had custom bits which integrated AWS and they used an old version; support issues came in for these versions and it was a pain to manage. (There was also a money issue here).

As a result Elastic the company licensed the new versions of the elastic code with a licence AWS wouldn’t be able to use.

So AWS forked the last Apache* version and continued its development in the Apache license. This is the result of that.