https://victorydntmd.tistory.com/308 https://esbook.kimjmin.net/03-cluster/3.2-index-and-shards
https://jaemunbro.medium.com/elastic-search-%EC%83%A4%EB%93%9C-%EC%B5%9C%EC%A0%81%ED%99%94-68062271fb64
