[[index-templates]]
= Index templates

NOTE: This topic describes the composable index templates introduced in {es} 7.8. 
For information about how index templates worked previously, 
see the <<indices-templates-v1,legacy template documentation>>.

[[getting]]
An index template is a way to tell {es} how to configure an index when it is created.
For data streams, the index template configures the stream's backing indices as they
are 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 data stream or index matches more than one index template, the index template with the highest priority is used.

[IMPORTANT]
====
{es} has built-in index templates for the `metrics-*-*`, `logs-*-*`, and `synthetics-*-*` index
patterns, each with a priority of `100`.
{ingest-guide}/fleet-overview.html[{agent}] uses these templates to
create data streams. If you use {agent}, assign your index templates a priority
lower than `100` to avoid an overriding the built-in templates.

Otherwise, to avoid accidentally applying the built-in templates, use a
non-overlapping index pattern or assign templates with an overlapping pattern a
`priority` higher than `100`.

For example, if you don't use {agent} and want to create a template for the
`logs-*` index pattern, assign your template a priority of `200`. This ensures
your template is applied instead of the built-in template for `logs-*-*`.
====

When a composable template matches a given index
it always takes precedence over a legacy template. If no composable template matches, a legacy
template may still match and be applied.

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 _component_template/component_template1
{
  "template": {
    "mappings": {
      "properties": {
        "@timestamp": {
          "type": "date"
        }
      }
    }
  }
}

PUT _component_template/other_component_template
{
  "template": {
    "mappings": {
      "properties": {
        "ip_address": {
          "type": "ip"
        }
      }
    }
  }
}

PUT _index_template/template_1
{
  "index_patterns": ["te*", "bar*"],
  "template": {
    "settings": {
      "number_of_shards": 1
    },
    "mappings": {
      "properties": {
        "host_name": {
          "type": "keyword"
        },
        "created_at": {
          "type": "date",
          "format": "EEE MMM dd HH:mm:ss Z yyyy"
        }
      }
    },
    "aliases": {
      "mydata": { }
    }
  },
  "priority": 200,
  "composed_of": ["component_template1", "other_component_template"],
  "version": 3,
  "_meta": {
    "description": "my custom"
  }
}
--------------------------------------------------
// TESTSETUP

////

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

////

include::simulate-multi-component-templates.asciidoc[]
