Elasticsearch Enable Shard Rebalance and Shard Allocation


Elasticsearch Enable Shard Rebalance and Shard Allocation

Opster Team

Nov 2020


In addition to reading this guide, run the free Elasticsearch Health Check-Up. Get actionable recommendations that can improve performance and prevent incidents (does not require any installation). Among the dozens of checks included are: shards sizes, search errors, thread pools, management queue size, circuit breakers and many more. Join over 700 users who use this free tool.

What does it mean?

Cluster shard rebalancing and allocation are often confused with each other.

Cluster shard allocation

This refers to the process by which any shard including new, recovered or rebalanced shards are allocated to Elasticsearch nodes. Cluster shard allocation may be temporarily disabled during maintenance in order to avoid shards from being relocated to nodes which are being restarted and may temporarily leave the cluster.

If cluster shard allocation is NOT enabled, then Elasticsearch will not be able to create new indices, recover corrupted indices or rebalance. This situation is very likely to cause data loss if not corrected quickly.

Cluster shard rebalancing

This refers to the process by which an Elasticsearch cluster may rebalance shards from nodes with high disk utilization (above the value of cluster.routing.allocation.disk.watermark.high) to nodes with lower disk utilisation, or redistribute shards from pre-existing nodes to a new node which has just been added to the cluster.  

If cluster shard rebalancing is not enabled, then Elasticsearch will not be able to optimize disk and cpu utilization across the cluster by rebalancing shards from heavily used nodes to underused nodes. 

How to resolve it

The default values are the recommended ones for both of these settings. To restore the default value run the following command:

PUT _cluster/settings
{
  "transient": {
     "cluster.routing.allocation.enable": "all",

     "cluster.routing.rebalance.enable": "all"
  }
}




Improve Elasticsearch Performance

Run The Analysis