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[Doc] Troubleshoot Cluster State / Linkable subsections #95468

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Apr 25, 2023
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[Doc] Troubleshoot Cluster State / Linkable subsections #95468

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29 changes: 22 additions & 7 deletions docs/reference/troubleshooting/common-issues/red-yellow-cluster-status.asciidoc
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Expand Up @@ -59,7 +59,9 @@ GET _cluster/allocation/explain?filter_path=index,node_allocation_decisions.node
A shard can become unassigned for several reasons. The following tips outline the
most common causes and their solutions.

**Re-enable shard allocation**
[discrete]
[[fix-cluster-status-reenable-allocation]]
===== Re-enable shard allocation

You typically disable allocation during a <<restart-cluster,restart>> or other
cluster maintenance. If you forgot to re-enable allocation afterward, {es} will
Expand All @@ -76,7 +78,9 @@ PUT _cluster/settings
}
----

**Recover lost nodes**
[discrete]
[[fix-cluster-status-recover-nodes]]
===== Recover lost nodes

Shards often become unassigned when a data node leaves the cluster. This can
occur for several reasons, ranging from connectivity issues to hardware failure.
Expand All @@ -94,7 +98,9 @@ asynchronously in the background.
POST _cluster/reroute?metric=none
----

**Fix allocation settings**
[discrete]
[[fix-cluster-status-allocation-settings]]
===== Fix allocation settings

Misconfigured allocation settings can result in an unassigned primary shard.
These settings include:
Expand All @@ -117,7 +123,9 @@ GET _cluster/settings?flat_settings=true&include_defaults=true
You can change the settings using the <<indices-update-settings,update index
settings>> and <<cluster-update-settings,cluster update settings>> APIs.

**Allocate or reduce replicas**
[discrete]
[[fix-cluster-status-allocation-replicas]]
===== Allocate or reduce replicas

To protect against hardware failure, {es} will not assign a replica to the same
node as its primary shard. If no other data nodes are available to host the
Expand All @@ -138,7 +146,10 @@ PUT _settings
----
// TEST[s/^/PUT my-index\n/]

**Free up or increase disk space**

[discrete]
[[fix-cluster-status-disk-space]]
===== Free up or increase disk space

{es} uses a <<disk-based-shard-allocation,low disk watermark>> to ensure data
nodes have enough disk space for incoming shards. By default, {es} does not
Expand Down Expand Up @@ -194,13 +205,17 @@ PUT _cluster/settings
----
// TEST[s/"30gb"/null/]

**Reduce JVM memory pressure**
[discrete]
[[fix-cluster-status-jvm]]
===== Reduce JVM memory pressure

Shard allocation requires JVM heap memory. High JVM memory pressure can trigger
<<circuit-breaker,circuit breakers>> that stop allocation and leave shards
unassigned. See <<high-jvm-memory-pressure>>.

**Recover data for a lost primary shard**
[discrete]
[[fix-cluster-status-restore]]
===== Recover data for a lost primary shard

If a node containing a primary shard is lost, {es} can typically replace it
using a replica on another node. If you can't recover the node and replicas
Expand Down