Elasticsearch Cluster Architecture

Sharding

Index split into N shards. Each shard is a Lucene index. Documents routed to shard by hash(id) mod N. Fixed at index creation.

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Index split into N shards. Each shard is a Lucene index. Documents routed to shard by hash(id) mod N. Fixed at index creation.

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Each shard has R replicas. Replicas serve reads + provide HA. If primary fails, replica promoted. Configurable per index.