﻿---
title: Index-level shard allocation settings
description: You can use shard allocation filters to control where Elasticsearch allocates shards of a particular index. These per-index filters are applied in conjunction...
url: https://www.elastic.co/elastic/docs-builder/docs/2855/reference/elasticsearch/index-settings/shard-allocation
products:
  - Elasticsearch
applies_to:
  - Elastic Stack: Generally available
---

# Index-level shard allocation settings
<admonition title="Settings supported in Serverless">
  Elastic Cloud Serverless projects [restrict the available Elasticsearch settings](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/2855/deploy-manage/deploy/elastic-cloud/differences-from-other-elasticsearch-offerings#elasticsearch-differences-serverless-settings-availability) to a supported subset, identified with a `Serverless` badge next to the setting name. For a complete list of available index settings, refer to the [Serverless index settings list](https://www.elastic.co/elastic/docs-builder/docs/2855/reference/elasticsearch/index-settings/serverless).
</admonition>

You can use shard allocation filters to control where Elasticsearch allocates shards of a particular index. These per-index filters are applied in conjunction with [cluster-wide allocation filtering](/elastic/docs-builder/docs/2855/reference/elasticsearch/configuration-reference/cluster-level-shard-allocation-routing-settings#cluster-shard-allocation-filtering) and [allocation awareness](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/2855/deploy-manage/distributed-architecture/shard-allocation-relocation-recovery/shard-allocation-awareness).
Shard allocation filters can be based on [custom node attributes](/elastic/docs-builder/docs/2855/reference/elasticsearch/configuration-reference/node-settings#custom-node-attributes) or the built-in `_name`, `_host_ip`, `_publish_ip`, `_ip`, `_host`, `_id`, `_tier` and `_tier_preference` attributes. [Index lifecycle management](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/2855/manage-data/lifecycle/index-lifecycle-management) uses filters based on custom node attributes to determine how to reallocate shards when moving between phases.
The `cluster.routing.allocation` settings are dynamic, enabling existing indices to be moved immediately from one set of nodes to another. Shards are only relocated if it is possible to do so without breaking another routing constraint, such as never allocating a primary and replica shard on the same node.
For example, you could use a custom node attribute to indicate a node’s performance characteristics and use shard allocation filtering to route shards for a particular index to the most appropriate class of hardware.

## Enabling index-level shard allocation filtering

To filter based on a custom node attribute:
1. Specify the filter characteristics with a custom node attribute in each node’s `elasticsearch.yml` configuration file. For example, if you have `small`, `medium`, and `big` nodes, you could add a `size` attribute to filter based on node size.
   ```yaml
   node.attr.size: medium
   ```
   You can also set custom attributes when you start a node:
   ```sh
   ./bin/elasticsearch -Enode.attr.size=medium
   ```
2. Add a routing allocation filter to the index. The `index.routing.allocation` settings support three types of filters: `include`, `exclude`, and `require`. For example, to tell Elasticsearch to allocate shards from the `test` index to either `big` or `medium` nodes, use `index.routing.allocation.include`:
   ```json

   {
     "index.routing.allocation.include.size": "big,medium"
   }
   ```
   
   If you specify multiple filters the following conditions must be satisfied simultaneously by a node in order for shards to be relocated to it:
   - If any `require` type conditions are specified, all of them must be satisfied
- If any `exclude` type conditions are specified, none of them may be satisfied
- If any `include` type conditions are specified, at least one of them must be satisfied
   For example, to move the `test` index to `big` nodes in `rack1`, you could specify:
   ```json

   {
     "index.routing.allocation.require.size": "big",
     "index.routing.allocation.require.rack": "rack1"
   }
   ```
   


## Index allocation filter settings

<definitions>
  <definition term="index.routing.allocation.include.{{attribute}}">
    Assign the index to a node whose `{{attribute}}` has at least one of the comma-separated values.
  </definition>
  <definition term="index.routing.allocation.require.{{attribute}}">
    Assign the index to a node whose `{{attribute}}` has *all* of the comma-separated values.
  </definition>
  <definition term="index.routing.allocation.exclude.{{attribute}}">
    Assign the index to a node whose `{{attribute}}` has *none* of the comma-separated values.
  </definition>
</definitions>

The index allocation settings support the following built-in attributes:
<definitions>
  <definition term="_name">
    Match nodes by node name
  </definition>
  <definition term="_host_ip">
    Match nodes by host IP address (IP associated with hostname)
  </definition>
  <definition term="_publish_ip">
    Match nodes by publish IP address
  </definition>
  <definition term="_ip">
    Match either `_host_ip` or `_publish_ip`
  </definition>
  <definition term="_host">
    Match nodes by hostname
  </definition>
  <definition term="_id">
    Match nodes by node id
  </definition>
  <definition term="_tier">
    Match nodes by the node’s [data tier](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/2855/manage-data/lifecycle/data-tiers) role. For more details see [data tier allocation filtering](https://www.elastic.co/elastic/docs-builder/docs/2855/reference/elasticsearch/index-settings/data-tier-allocation)
  </definition>
</definitions>

<note>
  `_tier` filtering is based on [node](https://www.elastic.co/elastic/docs-builder/docs/2855/reference/elasticsearch/configuration-reference/node-settings) roles. Only a subset of roles are [data tier](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/2855/manage-data/lifecycle/data-tiers) roles, and the generic [data role](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/2855/deploy-manage/distributed-architecture/clusters-nodes-shards/node-roles#data-node-role) will match any tier filtering.
</note>

You can use wildcards when specifying attribute values, for example:
```json

{
  "index.routing.allocation.include._ip": "192.168.2.*"
}
```