We have big Elasticsearch 2.x cluster which can't be upgraded right now, and I was working with cross-cluster search between 2.x and 6.x.
I tried 5.x as cross-cluster (and tribe), it works with 5 and 6, but it doesn't connect to 2. Even 5.0.0 doesn't.
I know that 2 is very old now and should be upgraded, but I'm searching for a temporary solution for cross-search between Elasticsearch 2.x and newer versions.
Did anyone have this problem? Third-party solutions like kind of proxying is also ok for me.
This solution is temporary, I think this cluster can be upgraded (the problem is we can't have downtime now, but upgrade from 2.x to any newer needs full cluster restart).