Elasticsearch Unassigned Shards: Why and How to Fix

How to fix it

Try these in order — the most common fix is first.

1. 1. Ask Elasticsearch why

   Copy steps
   1. Run GET _cluster/allocation/explain, optionally with {"index":"my-index","shard":0,"primary":false}
   2. Read the decider that returned NO
   Did this fix it? Yes No

2. 2. Retry and reset

   Copy steps
   1. POST _cluster/reroute?retry_failed=true to retry shards that hit max allocation retries
   2. Review index and cluster settings for stale allocation filters
   Did this fix it? Yes No

3. 3. Fix capacity

   Copy steps
   1. Add a data node to the same tier or lower index.number_of_replicas
   2. Free disk with GET _cat/allocation, delete old indices, force merge or shrink read-only indices
   Did this fix it? Yes No

Symptoms

GET _cat/shards shows UNASSIGNED; cluster health is yellow or red; unassigned_shards is above zero.

Why it happens

• Replica count higher than available data nodes
• Disk watermarks exceeded
• cluster.routing.allocation.enable set to none
• Allocation filtering or awareness settings that match no node
• Lost primary with no valid copy

This guide also covers

• elasticsearch unassigned shards
• elasticsearch allocation explain
• elasticsearch shards not allocating

Other Elasticsearch errors

• Elasticsearch Cluster Health Yellow: Causes and Fixes
• Elasticsearch Cluster Health Red: How to Fix It
• Elasticsearch circuit_breaking_exception: Data Too Large
• Elasticsearch High JVM Memory Pressure and Out of Memory
• Elasticsearch Disk Watermark: Index Read-Only (FORBIDDEN/12)
• Elasticsearch Limit of Total Fields [1000] Exceeded
• Why Is Elasticsearch So Slow? Fixing Slow Searches
• Elasticsearch Cannot Change Field Mapping: Reindex Guide