Elasticsearch OpenSearch Routing

By Opster Team

Updated: Mar 29, 2023

| 1 min read

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.

Before you begin reading this guide, we recommend you try running the OpenSearch Error Check-Up which analyzes 2 JSON files to detect errors.

To evaluate your use OpenSearch routing and effortlessly resolve issues in your deployment, we recommend you try AutoOps for OpenSearch. AutoOps diagnoses problems by analyzing hundreds of metrics collected by a lightweight agent and offers guidance for resolving them.


In OpenSearch, routing refers to document routing. When you index a document, OpenSearch will determine which shard the document should be routed to for indexing. 

The shard is selected based on the following formula:

shard = hash(_routing) % number_of_primary_shards

Where the default value of _routing is _id.
It is important to know which shard the document is routed to because OpenSearch will need to determine where to find that document later on for document retrieval requests. 


In twitter index with 2 primary shards, the document with _id equal to “440” gets routed to the shard number:   

shard = hash( 440 ) % 2
PUT twitter/_doc/440

Notes and good things to know

  • In order to improve search speed, you can create custom routing. For example, you can enable custom routing that will ensure that only a single shard will be queried (the shard that contains your data).
  • To create custom routing in OpenSearch, you will need to configure and define that not all routing will be completed by default settings. ( v <= 5.0)
PUT my_index/customer/_mapping
  •  This will ensure that every document in the “customer” type must specify a custom routing. 

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