We have an Elasticsearch cluster in version 6. We are planning an upgrade to version 7. For one of our applications, we are using Elastic's JDBC client to get data from ES. We have unfortunately no other way to query the data in that application.
The problem we have is that there is no version of the JDBC client we could find which can communicate with both ES 6 and ES 7. This means if we change the client we use before the upgrade it wouldn't work until we upgrade ES. And if we upgrade before changing the client it won't work until the client is changed.