Elasticsearch Cluster Health Yellow: Causes and Fixes

How to fix it

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

1. 1. Find out why with the allocation explain API

   Copy steps
   1. Run GET _cat/shards?v and look for UNASSIGNED rows (prirep r = replica)
   2. Run GET _cluster/allocation/explain with the index, shard number and primary:false
   Did this fix it? Yes No

2. 2. Single node: drop replicas to 0

   Copy steps
   1. PUT my-index/_settings with index.number_of_replicas set to 0
   2. Only do this if you accept no redundancy; add a second data node for production
   Did this fix it? Yes No

3. 3. Re-enable allocation if it was turned off

   Copy steps
   1. GET _cluster/settings and check cluster.routing.allocation.enable
   2. If it is none, PUT _cluster/settings with persistent cluster.routing.allocation.enable set to null
   Did this fix it? Yes No

4. 4. Add capacity or free disk

   Copy steps
   1. Check GET _cat/allocation
   2. Add a data node, delete unneeded indices, or lower number_of_replicas so it fits the node count
   Did this fix it? Yes No

Symptoms

GET _cluster/health returns status yellow and unassigned_shards greater than 0; Kibana shows a yellow cluster or index.

Why it happens

• Single-node cluster, so replicas have nowhere to go
• More replicas configured than data nodes
• A node left the cluster (restart, long GC pause, network)
• Disk low watermark (85% by default) reached
• Allocation left disabled after maintenance

This guide also covers

• elasticsearch cluster health yellow
• elasticsearch yellow status fix
• elasticsearch replica unassigned single node

Other Elasticsearch errors

• Elasticsearch Cluster Health Red: How to Fix It
• Elasticsearch Unassigned Shards: Why and How to Fix
• 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