Distributed indexing

Indexing process

1. When you index a document, the node that receives your HTTP request determines which shard should contain your document, based on a hash of the document’s ID.
2. Then, it forwards the document to the node holding that primary shard.
3. Once the shard is updated, the document is sent to be indexed in all replicas of that shard.
4. Finally, the indexing command returns after all replicas are updated.

This process keeps replicas in sync and allows them to serve searches and to be promoted to primary shards in case the original primary is unavailable.