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default	Index Templates	OpenSearch	5

Index template

Index templates let you initialize new indices with predefined mappings and settings. For example, if you continuously index log data, you can define an index template so that all of these indices have the same number of shards and replicas.

OpenSearch switched from _template to _index_template in version 7.8. Use _template for older versions of OpenSearch. {: .note }

TOC {:toc}

Create template

To create an index template, use a POST request:

POST _index_template

This command creates a template named daily_logs and applies it to any new index whose name matches the regular expression logs-2020-01-* and also adds it to the my_logs alias:

PUT _index_template/daily_logs
{
  "index_patterns": [
    "logs-2020-01-*"
  ],
  "template": {
    "aliases": {
      "my_logs": {}
    },
    "settings": {
      "number_of_shards": 2,
      "number_of_replicas": 1
    },
    "mappings": {
      "properties": {
        "timestamp": {
          "type": "date",
          "format": "yyyy-MM-dd HH:mm:ss||yyyy-MM-dd||epoch_millis"
        },
        "value": {
          "type": "double"
        }
      }
    }
  }
}

You should see the following response:

{
  "acknowledged": true
}

If you create an index named logs-2020-01-01, you can see that it has the mappings and settings from the template:

PUT logs-2020-01-01
GET logs-2020-01-01

{
  "logs-2020-01-01": {
    "aliases": {
      "my_logs": {}
    },
    "mappings": {
      "properties": {
        "timestamp": {
          "type": "date",
          "format": "yyyy-MM-dd HH:mm:ss||yyyy-MM-dd||epoch_millis"
        },
        "value": {
          "type": "double"
        }
      }
    },
    "settings": {
      "index": {
        "creation_date": "1578107970779",
        "number_of_shards": "2",
        "number_of_replicas": "1",
        "uuid": "U1vMDMOHSAuS2IzPcPHpOA",
        "version": {
          "created": "7010199"
        },
        "provided_name": "logs-2020-01-01"
      }
    }
  }
}

Any additional indices that match this pattern---logs-2020-01-02, logs-2020-01-03, and so on---will inherit the same mappings and settings.

Retrieve template

To list all index templates:

GET _cat/templates

To find a template by its name:

GET _index_template/daily_logs

To get a list of all your templates:

GET _index_template/daily_logs

To get a list of all templates that match a pattern:

GET _index_template/daily*

To check if a specific template exists:

HEAD _index_template/<name>

Configure multiple templates

You can create multiple index templates for your indices. If the index name matches more than one template, OpenSearch merges all mappings and settings from all matching templates and applies them to the index.

The settings from the more recently created index templates override the settings of older index templates. So, you can first define a few common settings in a generic template that can act as a catch-all and then add more specialized settings as required.

An even better approach is to explicitly specify template priority using the order parameter. OpenSearch applies templates with lower priority numbers first and then overrides them with templates that have higher priority numbers.

For example, say you have the following two templates that both match the logs-2020-01-02 index and there’s a conflict in the number_of_shards field:

Template 1

PUT _index_template/template-01
{
  "index_patterns": [
    "logs*"
  ],
  "priority": 0,
  "template": {
    "settings": {
      "number_of_shards": 2
    }
  }
}

Template 2

PUT _index_template/template-02
{
  "index_patterns": [
    "logs-2020-01-*"
  ],
  "priority": 1,
  "template": {
    "settings": {
      "number_of_shards": 3
    }
  }
}

Because template-02 has a higher priority value, it takes precedence over template-01 . The logs-2020-01-02 index would have the number_of_shards value as 3.

Delete template

You can delete an index template using its name, as shown in the following command:

DELETE _index_template/daily_logs

Index template options

You can specify the options shown in the following table:

Option	Type	Description	Required
`priority`	`Number`	Specify the priority of the index template.	No
`create`	`Boolean`	Specify whether this index template should replace an existing one.	No

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