[[indices-simulate-index]]
=== Simulate index API
++++
<titleabbrev>Simulate index</titleabbrev>
++++

experimental[]

Returns the index configuration that would be applied to the specified index from an 
existing <<index-templates, index template>>.

////
[source,console]
--------------------------------------------------
PUT _index_template/template_1
{
  "index_patterns": ["my-index-*"],
  "template": {
    "settings": {
      "number_of_shards": 1
    }
  }
}
--------------------------------------------------
// TESTSETUP

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

[source,console]
--------------------------------------------------
POST /_index_template/_simulate_index/my-index-000001
--------------------------------------------------

[[simulate-index-api-request]]
==== {api-request-title}

`POST /_index_template/_simulate_index/<index>`

[[simulate-index-api-prereqs]]
==== {api-prereq-title}

* If the {es} {security-features} are enabled, you must have the
`manage_index_templates` or `manage` <<privileges-list-cluster,cluster
privilege>> to use this API.

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

`<index>`::
(Required, string)
Name of the index to simulate. 

[[simulate-index-api-query-params]]
==== {api-query-parms-title}
////
`cause`::
(Optional, string) The reason for running the simulation. 
////

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

[role="child_attributes"]
[[simulate-index-api-response-body]]
==== {api-response-body-title}

`overlapping`::
(array) Any templates that also matched the index but were superseded by a higher-priority template.
Response includes an empty array if there are no overlapping templates. 
+
.Properties of `overlapping`
[%collapsible%open]
====
`name`::
(string) Name of the superseded template.

`index_patterns`:: 
(array) Index patterns that the superseded template applies to.
====

`template`::
(object)
The settings, mappings, and aliases that would be applied to the index. 
+
.Properties of `template`
[%collapsible%open]
====
include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=aliases]
+
Response includes an empty object if no aliases would be applied. 

include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=mappings]
+
Omitted from the response if no mappings would be applied.

include::{es-ref-dir}/rest-api/common-parms.asciidoc[tag=settings]
+
Response includes an empty object if no settings would be applied. 
====

[[simulate-index-api-example]]
==== {api-examples-title}

The following example shows the configuration that would be applied to `my-index-000001` by 
an existing template.

[source,console]
--------------------------------------------------
PUT /_component_template/ct1                    <1>
{
  "template": {
    "settings": {
      "index.number_of_shards": 2
    }
  }
}

PUT /_component_template/ct2                    <2>
{
  "template": {
    "settings": {
      "index.number_of_replicas": 0
    },
    "mappings": {
      "properties": {
        "@timestamp": {
          "type": "date"
        }
      }
    }
  }
}

PUT /_index_template/final-template             <3>
{
  "index_patterns": ["my-index-*"],
  "composed_of": ["ct1", "ct2"],
  "priority": 5
}

POST /_index_template/_simulate_index/my-index-000001 <4>
--------------------------------------------------
<1> Create a component template (`ct1`) that sets the number of shards to 2
<2> Create a second component template (`ct2`) that sets the number of replicas to 0 and defines a mapping
<3> Create an index template (`final-template`) that uses the component templates
<4> Show the configuration that would be applied to `my-index-000001`

The response shows the index settings, mappings, and aliases applied by the `final-template`:

[source,console-result]
---------------------------------------------------------
{
  "template" : {
    "settings" : {
      "index" : {
        "number_of_shards" : "2",
        "number_of_replicas" : "0"
      }
    },
    "mappings" : {
      "properties" : {
        "@timestamp" : {
          "type" : "date"
        }
      }
    },
    "aliases" : { }
  },
  "overlapping" : [
    {
      "name" : "template_1",
      "index_patterns" : [
        "my-index-*"
      ]
    }
  ]
}
---------------------------------------------------------
