We are currently running a few production clusters in ES 5.5.1.
We will soon migrate our data in ES 6.x (wichever will be the latest at that time) to take advantage of the new features, some of wich looks particulary interesting for our use cases.
However, as much as our data could happily migrate in ES 6.x without difficulty, I'd like to plan for the future ES 7.x by making all my multi-types indices mono-type. So far, so good, the only indices that have several types are small metadata and userdata indices, and the reindex API is more than up to the task.
However, I wonder about our data indices. They are quite big, and full of very complex documents (1000+ fields, 17 collections, 4 levels of imbrication). All those indices are already mono-type .. but of course, their type isn't "_doc", but a custom-named type. Will they be conform with ES 7.x as they are, or will I have to reindex everything, changing their types to "_doc"?
I might be ahead of schedule, but any info on the matter would be appreciated.