we want to upgrade our elasticsearch version from 5.6 to 7.9 in our project.
I have to migrate our indexes and docs to new version but I cant use reindex, So I rest high level client to connect to elasticsearch 7 and use http request for elasticsearch 5.
For migration I get part of docs with match_all query and scroll from old version and index them in new elasticsearch with bulk request.
our old version elasticsearch has 3 node.My question is that I have to send request to all node separately and process docs or if I send match_all query search to one node it will be handled by elsaticsearch (I read sth about cordinating node that handle requests and Every node is implicitly a coordinating node cordinating node.) or I have to send request to data node