The notion of Open Distro for ES being "a fork" is, in my opinion and as of last I checked, overblown. Yes, they bundle a bunch of freely licensed stuff to make up for features that Elastic themselves have paywalled off (or sealed behind their free-to-use, but non-libre, custom license where they don't show/include sources either), but they rely on and effectively install the (hitherto) Apache-licensed upstream release of ElasticSearch, as published by Elastic.

Also, if you take a closer look at Open Distro, you will quickly come to the conclusion that you really do not want to deploy what drops out of there. The RPM package does CRAZY stuff that made me exhale audibly enough for coworkers to notice - like spawning a postinstall shellscript that `wget`s a .so for/from an optional library that the Open Distro release team put into an S3 bucket, and then `mv`ing that downloaded file (iirc even without any content verification; so the content could be your proxy's captive portal markup, for all they know) into (again, iirc) /usr/lib. That is from WITHIN AN RPM PACKAGE, mind you, where you could and should really just carry that file yourself.

That and other minor troubles with the tooling surrounding the actual product (ES) made me abandon Open Distro fairly quickly. Which is a shame, since a really freely licensed spin of ES with "Enterprise" features would indeed be very nice to have.