[Elasticsearch] Elasticsearch document is routed to shard

1. Data routing (routing)

What does it mean to route document to shard?

Data routing (routing): The data of an index will be divided into multiple pieces, and each piece is in a shard; therefore, a document can only exist in one shard. When creating a document, es needs to determine which shard to place the document on the index. This process is called document routing (data routing).

2. Routing Algorithm

shard = hash