Elasticsearch Replication

Elasticsearch Replication

Opster Team

March 2021

In addition to reading this guide, we recommend you run the Elasticsearch Health Check-Up. It will detect issues and improve your Elasticsearch performance by analyzing your shard sizes, threadpools, memory, snapshots, disk watermarks and more.

The Elasticsearch Check-Up is free and requires no installation.

Run the Elasticsearch check-up to receive recommendations like this:

checklist Run Check-Up

The following configuration error was detected on node 123...



This error can have a severe impact on your system. It's important to understand that it was caused by...



In order to resolve this issue and prevent it from occurring again, we recommend that you begin by changing the configuration to...


X-PUT curl -H "Content-Type: application/json" [customized recommendation]


Replication refers to storing a redundant copy of the data. Starting from version 7.x, Elasticsearch creates one primary shard with a replication factor set to 1.  Replicas never get assigned to the same node on which primary shards are assigned, which means you should have at least two nodes in the cluster to assign the replicas. If a primary shard goes down, the replica automatically acts as a primary shard.

What it is used for

Replicas are used to provide high availability and failover. A higher number of replicas is also helpful for faster searches.


Update replica count

PUT /api-logs/_settings?pretty
    "index" : {
        "number_of_replicas" : 2

Common problems

  • By default, new replicas are not assigned to nodes with more than 85% disk usage. Instead, Elasticsearch throws a warning.
  • Creating too many replicas may cause a problem if there are not enough resources available in the cluster. 

Related log errors to this ES concept

Failed to send response
Failed to send response for
Actual Exception
failed to perform on node
Failed to send error message back to client for action
Unexpected error during the primary phase for action ; request
unexpected error while failing replica
Unexpected error while replicating for action . shard .
Failed to perform
Failed to send error response for action
Unexpected error during the primary phase for action

Run the Check-Up to get a customized report like this:

Analyze your cluster