This section describes how to analyze unassigned shards using the Elasticsearch APIs and Kibana.

Elasticsearch distributes the documents in an index across multiple shards and distributes copies of those shards across multiple nodes in the cluster. This both increases capacity and makes the cluster more resilient, ensuring your data remains available if a node goes down.

A healthy (green) cluster has a primary copy of each shard and the required number of replicas are assigned to different nodes in the cluster.

If a cluster has unassigned replica shards, it is functional but vulnerable in the event of a failure. The cluster is unhealthy and reports a status of yellow.

If a cluster has unassigned primary shards, some of your data is unavailable. The cluster is unhealthy and reports a status of red.

A formerly-healthy cluster might have unassigned shards because nodes have dropped out or moved, are running out of disk space, or are hitting allocation limits.

If a cluster has unassigned shards, you might see an error message such as this on the Elastic Cloud console:

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