Shard Allocation and Rebalancing
Understand how Elasticsearch decides where shards live, how allocation awareness spreads replicas across hardware, and how to control rebalancing during scaling and maintenance.
Where Do Shards Go?
When you create an index or add a node, Elasticsearch must decide which node holds each shard. This process is shard allocation, and keeping it balanced is key to a healthy, performant cluster.
The Allocation Process
The master node runs allocation deciders for every unassigned shard. They check disk space, shard count, awareness rules, and filters before placing a shard. Failing any decider keeps the shard UNASSIGNED.
All lessons in this course
- Sharding and Replicas Explained
- Cluster Health and Monitoring
- Node Roles and Architecture
- Shard Allocation and Rebalancing