As I argued elsewhere in this thread this is completely untrue. Amazon ships an Elastic provided OSS build of Elasticsearch unmodified and as is. There is no fork repo in the opendistro account. There is no ambiguity in the upstream repo (it's a nicely documented code base).
Amazon is shipping and forking the elastic suite of tools, you are describing Elasticsearch itself.
When licensing is at a source file level that is ambiguous for sysadmins. I understand you are approaching this as a developer, where it might be very clear.
There is no Amazon fork of the Elasticsearch repository. I looked at their repositories. they are copying the oss build of elasticsearch unmodified, without patches.
As for the licensing; licensing is documented in a 10 line LICENSE.txt. Also, it would be hard to miss the license settings, when you set this up. Hard to miss unless you are a seriously dyslexic and negligent person. In which case, I'd argue the Elastic basic license is the least of your problems.
