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Feb 10, 2022 · Operations

Elasticsearch Allocation Deciders: Overview, Configuration, and Core Algorithms

Elasticsearch’s AllocationDecider abstract class powers dynamic shard placement, with concrete deciders—such as awareness, rebalance, disk‑threshold, filter, version, and snapshot—controlling node selection, replication, and movement, while the AllocationService and its default BalancedShardsAllocator use weighted balance formulas to allocate, relocate, and rebalance shards whenever index changes, settings updates, or cluster state transitions occur.