Re-index in ElasticSearch with zero downtime

Hi Everyone,

We use Elasticsearch 7.9, time to time we may need to do re-indexing. We are using aliases and the applications are pointing to alias instead of real index. I read some articles and it looks in most cases we would lose some update's/deletes that happen during the re-indexing process.

based on what I read, Below are the steps that I am planning to do.

Note : old_index is pointing to index-alias(it's alias name)

1- create new index(new_index) 2- do re-indexing from old_index to new_index 3- point the alias(index-alias) to new_index 4- Do second round of re-indexing from old_index to new_index

below are some of issues with this approach:

1- Two round of re-indexing needs to be done. This will become problematic, if we have large data in that index. 2- After step (3) , we may lose some of the deletes/updates on new_index.

What is the best method to do re-indexing with zero downtime and minimal impact for end-users?

Thanks in advance.