How does elasticsearch reindexing behave when data keeps being written to the source index?

Question

I want to use the elasticsearch reindex api to reindex an index on prod.

What is the behaviour when I keep writing to the source index? Will the reindexing task keep reindexing as long as I still write to it?

Answer 1

The reindex process will reindex only the documents that exist in the source index at the time when the reindex request was made.

Any document created or updated after the reindex request was made will not be indexed in the destination index, you will need to run another reindex to get these documents.

So, if you keep writing to the index, you will need to keep doing reindexes.