OpenSearch/docs/reference/indices/index-templates.asciidoc

[[indices-templates]]
=== Index template API
++++
<titleabbrev>Index template</titleabbrev>
++++

This documentation is about V2 (version 2) index templates. For V1 templates please see the
<<indices-templates-v1,V1 template documentation>>.

[NOTE]
====
In {es} 7.8 the `prefer_v2_templates` querystring parameter was introduced to the index, update,
bulk, and create index APIs to allow configuring whether to favor V2 or V1 index templates. In 7.x
the default value for this parameter is `false` meaning that the <<indices-templates-v1,V1 index
templates>> take precedence. In 8.x the default value for the parameter is `true` meaning that V2
index templates take precedence (V1 templates may still match if no V2 template matches).
====

An index template is a way to tell {es} how to configure an index when it is created. Templates are
configured prior to index creation and then when an index is created either manually or through
indexing a document, the template settings are used as a basis for creating the index.

There are two types of templates, index templates and <<indices-component-template,component
templates>>. Component templates are reusable building blocks that configure mappings, settings, and
aliases. You use component templates to construct index templates, they aren't directly applied to a
set of indices. Index templates can contain a collection of component templates, as well as directly
specify settings, mappings, and aliases.

If a new index matches more than one index template, the index template with the highest priority is used.

If an index is created with explicit settings and also matches an index template, 
the settings from the create index request take precedence over settings specified in the index template and its component templates.

[source,console]
--------------------------------------------------
PUT _index_template/template_1
{
  "index_patterns": ["te*", "bar*"],
  "template": {
    "settings": {
      "number_of_shards": 1
    },
    "mappings": {
      "_source": {
        "enabled": false
      },
      "properties": {
        "host_name": {
          "type": "keyword"
        },
        "created_at": {
          "type": "date",
          "format": "EEE MMM dd HH:mm:ss Z yyyy"
        }
      }
    },
    "aliases": {
      "mydata": { }
    }
  },
  "priority": 10,
  "composed_of": ["component_template1", "other_component_template"],
  "version": 3,
  "_meta": {
    "description": "my custom"
  }
}
--------------------------------------------------
// TESTSETUP

//////////////////////////

[source,console]
--------------------------------------------------
DELETE _index_template/template_*
DELETE _component_template/*
--------------------------------------------------
// TEARDOWN

//////////////////////////

[[put-index-template-api-request]]
==== {api-request-title}

`PUT /_index_template/<index-template>`


[[put-index-template-api-desc]]
==== {api-description-title}

Creates or updates an index template. 

// tag::index-template-def[]
Index templates define <<index-modules-settings,settings>> and <<mapping,mappings>> that you can
automatically apply when creating new indices. {es} applies templates to new indices based on an
index pattern that matches the index name.
// end::index-template-def[]

Index templates are only applied during index creation. Changes to index templates do not affect
existing indices. Settings and mappings specified in <<indices-create-index, create index>> API
requests override any settings or mappings specified in an index template.

===== Comments in index templates
You can use C-style /* */ block comments in index templates. You can include comments anywhere in
the request body, except before the opening curly bracket.

[[getting]]
===== Getting templates

[[indices-get-template]]
=== Get index template API
++++
<titleabbrev>Get index template</titleabbrev>
++++

Returns information about one or more index templates.

[source,console]
--------------------------------------------------
GET /_index_template/template_1
--------------------------------------------------


[[get-template-api-request]]
==== {api-request-title}

`GET /_index_template/<index-template>`


[[get-template-api-path-params]]
==== {api-path-parms-title}

include::{docdir}/rest-api/common-parms.asciidoc[tag=index-template]
+
To return all index templates, omit this parameter or use a value of `*`.


[[get-template-api-query-params]]
==== {api-query-parms-title}

include::{docdir}/rest-api/common-parms.asciidoc[tag=flat-settings]

include::{docdir}/rest-api/common-parms.asciidoc[tag=local]

include::{docdir}/rest-api/common-parms.asciidoc[tag=master-timeout]


[[get-template-api-example]]
==== {api-examples-title}


[[get-template-api-wildcard-ex]]
===== Get index templates using a wildcard expression

[source,console]
--------------------------------------------------
GET /_index_template/temp*
--------------------------------------------------


[[get-template-api-all-ex]]
===== Get all index templates

[source,console]
--------------------------------------------------
GET /_index_template
--------------------------------------------------

[[put-index-template-api-path-params]]
==== {api-path-parms-title}

`<index-template>`::
(Required, string)
Name of the index template to create.


[[put-index-template-api-query-params]]
==== {api-query-parms-title}

`create`::
(Optional, boolean)
If `true`, this request cannot replace or update existing index templates. Defaults to `false`.

include::{docdir}/rest-api/common-parms.asciidoc[tag=master-timeout]


[[put-index-template-api-request-body]]
==== {api-request-body-title}

`index_patterns`::
(Required, array of strings)
Array of wildcard expressions
used to match the names of indices during creation.

include::{docdir}/rest-api/common-parms.asciidoc[tag=aliases]

include::{docdir}/rest-api/common-parms.asciidoc[tag=mappings]

include::{docdir}/rest-api/common-parms.asciidoc[tag=settings]

`template`::
(Optional, object)
This is the template to be applied, may optionally include a `mappings`,
`settings`, or `aliases` configuration.

`composed_of`::
(Optional, array of strings)
An ordered list of component template names. Component templates will be merged in the order
specified, meaning that the last component template specified has the highest precedence. See the
<<indices-component-template,component template>> reference for information.

`priority`::
(Optional, integer)
Priority to determine index template precedence when a new index is created. The index template with
the highest priority is chosen.
This number is not automatically generated by {es}.

`version`::
(Optional, integer)
Version number used to manage index templates externally.
This number is not automatically generated by {es}.

`_meta`::
(Optional, object)
Optional user metadata about the index template. May have any contents.
This map is not automatically generated by {es}.

[[put-index-template-api-example]]
==== {api-examples-title}

==== Composing multiple component templates

When multiple component templates are specified in the `composed_of` field for an index template,
they are merged in the order specified, meaning that later component templates override earlier
component templates.

For two component templates:

[source,console]
--------------------------------------------------
PUT /_component_template/template_with_2_shards
{
  "template": {
    "settings": {
      "index.number_of_shards": 2
    }
  }
}
--------------------------------------------------

[source,console]
--------------------------------------------------
PUT /_component_template/template_with_3_shards
{
  "template": {
    "settings": {
      "index.number_of_shards": 3
    }
  }
}
--------------------------------------------------

The order they are specified changes the number of shards for an index:

[source,console]
--------------------------------------------------
PUT /_index_template/template_1
{
  "index_patterns": ["t*"],
  "composed_of": ["template_with_2_shards", "template_with_3_shards"]
}
--------------------------------------------------

In this case, an index matching `t*` will have three primary shards. If the order of composed
templates were reversed, the index would have two primary shards.

===== Index template with index aliases

You can include <<indices-aliases,index aliases>> in an index template.

[source,console]
--------------------------------------------------
PUT _index_template/template_1
{
  "index_patterns" : ["te*"],
  "template": {
    "settings" : {
        "number_of_shards" : 1
    },
    "aliases" : {
        "alias1" : {},
        "alias2" : {
            "filter" : {
                "term" : {"user" : "kimchy" }
            },
            "routing" : "kimchy"
        },
        "{index}-alias" : {} <1>
    }
  }
}
--------------------------------------------------
<1> the `{index}` placeholder in the alias name will be replaced with the
actual index name that the template gets applied to, during index creation.


[[multiple-templates]]
===== Indices matching multiple templates

When an index is created that matches multiple index templates, only the index template with the
highest priority is applied. For example:

[source,console]
--------------------------------------------------
PUT /_index_template/template_1
{
  "index_patterns" : ["t*"],
  "priority" : 0,
  "template": {
    "settings" : {
      "number_of_shards" : 1,
      "number_of_replicas": 0
    },
    "mappings" : {
      "_source" : { "enabled" : false }
    }
  }
}

PUT /_index_template/template_2
{
  "index_patterns" : ["te*"],
  "priority" : 1,
  "template": {
    "settings" : {
      "number_of_shards" : 2
    },
    "mappings" : {
      "_source" : { "enabled" : true }
    }
  }
}
--------------------------------------------------

For indices that start with `te*`, `_source` will enabled, and the index will have two primary
shards and one replica, because only `template_2` will be applied.

NOTE: Multiple templates with overlapping index patterns at the same priority are not allowed, and
an error will be thrown when attempting to create a template matching an existing index template at
identical priorities.


[[versioning-templates]]
===== Template versioning

You can use the `version` parameter to add an optional version number to an index template. External
systems can use these version numbers to simplify template management.

The `version` parameter is completely optional and not automatically generated by {es}.

To unset a `version`, replace the template without specifying one.

[source,console]
--------------------------------------------------
PUT /_index_template/template_1
{
  "index_patterns" : ["foo", "bar"],
  "priority" : 0,
  "template": {
    "settings" : {
        "number_of_shards" : 1
    }
  },
  "version": 123
}
--------------------------------------------------

To check the `version`, you can use the <<indices-get-template, get index template>> API.

[[template-metadata]]
===== Template metadata

You can use the `_meta` parameter to add optional metadata to an index template. This is a
user-defined map that can contain any data. This data will be stored in the cluster state however,
so keeping it short is preferrable.

The `_meta` parameter is completely optional and not automatically generated by {es}.

To unset `_meta`, replace the template without specifying one.

[source,console]
--------------------------------------------------
PUT /_index_template/template_1
{
  "index_patterns": ["foo", "bar"],
  "template": {
    "settings" : {
        "number_of_shards" : 3
    }
  },
  "_meta": {
    "description": "set number of shards to three",
    "serialization": {
      "class": "MyIndexTemplate",
      "id": 17
    }
  }
}
--------------------------------------------------

To check the `_meta`, you can use the <<indices-get-template, get index template>> API.