Elasticsearch Replication



Elasticsearch Replication

Opster Team

July 2020, Version: 1.7-7.9


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Replication in Elasticsearch

What it is

Replication refers to storing the 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 on 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.

Examples

Update replication count

PUT /api-logs/_settings?pretty
{
    "index" : {
        "number_of_replicas" : 2
    }
}
Common problems
  • By default, If free disk space usage reaches 85%, the replicas of newly created indices are not assigned on that node and 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



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