Reindexing from source data is not the only option, however, I would say it’s probably the best one in terms of quality and easiness
Other options are:
- Reindex from remote. The caveat here is - that your
_source
on the original cluster should be enabled, otherwise it wouldn’t be possible, since reindexing is basically taking the _source
content and indexing it once again
- Restoring snapshot made on the old cluster. Snapshots are effectively copy of Elastic files, so, unfortunately there are limitations: snapshots of indices created in 1.x cannot be restored to 5.x or 6.x, and snapshots of indices created in 2.x cannot be restored to 6.x. But, even if you’re in the situation like this - you still should be able to migrate snapshots via intermediate suitable Elastic version