# Index Templates

Index templates provide a way to ensure your indices are mapped correctly upon creation. You may control both settings and individual field mappings within your documents.

{% hint style="info" %}
Check out Elasticsearch's [Index Templates documentation](https://www.elastic.co/guide/en/elasticsearch/reference/current/index-templates.html) for further reading.
{% endhint %}

## Component Templates

In order to map your indices, you must first create a [component template](https://www.elastic.co/guide/en/elasticsearch/reference/current/indices-component-template.html) which includes your mappings and (optionally) settings for the index. You may use the [Mapping Builder](/indices/mapping-builder.md) to create your mapping DSL or provide it in the form of a DSL struct.

```js
var mappings = getInstance( "MappingBuilder@cbelasticsearch" )
                    .create( function( mapping ){
                        mapping.keyword( "id" );
                        mapping.text( "description" );
                        mapping.date( "@timestamp" );
                        mapping.object( "meta", function( mapping ){
                            mapping.date( "createdTime" ).format( "date_time_no_millis" );
                            mapping.date( "modifiedTime" ).format( "date_time_no_millis" );
                            mapping.text( "changelog" );
                            mapping.keyword( "createdBy" );
                            mapping.keyword( "modifiedBy" );
                        } );
                    } );

getInstance( "Client@cbelasticsearch" ).applyComponentTemplate(
    "my-component-template",
    { 
        "template" :{
            "settings" : {
                    "index.refresh_interval" : "5s",
                    "number_of_replicas"     : 0,
                    "number_of_shards"       : 1,
                    "index.lifecycle.name"   : "my-lifecycle-policy"
            },
            "mappings" : mappings.toDSL()
        }
    }
);
```

Additional methods are available for managing component templates:

* `getInstance( "Client@cbelasticsearch" ).componentTemplateExists( [ template name] )`
* `getInstance( "Client@cbelasticsearch" ).getComponentTemplate( [ template name] )`
* `getInstance( "Client@cbelasticsearch" ).deleteComponentTemplate( [ template name] )`

Note that a component template may not be deleted if it is in use by an Index template. In order to delete it, you must first delete the index template.

## Index Templates

Now that we have created a component template, we can use it in an [Index template](https://www.elastic.co/guide/en/elasticsearch/reference/current/index-templates.html). Index templates define a matching index ( or Data Stream ) name pattern to which any new indexes created with this naming pattern will have the template applied. Multiple component templates may be used in an array.

Note, that if a `data_stream` key is provided in the definition, any writes to a matching index pattern will be created as a data stream.

```js
getInstance( "Client@cbelasticsearch" ).applyIndexTemplate(
    // the index template name
    "my-index-template",
    {
        // The pattern of the inbound index to apply this template. Only applies the template to newly created indices
        "index_patterns" : [ "my-index-*" ],
        "composed_of" : [
            // some other component template
            "other-component-template",
            "my-component-template" 
        ],
        // The presence of this key creates a data stream for any matching index pattern. If it is absent an index will be created when data is received
        "data_stream" : {},
        // A priority - allows you to prioritize the order in which templates are applied with similar patterns
        "priority" : 150,
        // An optional struct of arbitrary meta information for the template
        "_meta" : {
            "description" : "My global index template"
        }
    }
);
```

All Component and Index template updates are applied as *upsert* operations - meaning that the `@version` key will be incremented if a new version of a template is applied.

Additional methods are available for managing idnex templates:

* `getInstance( "Client@cbelasticsearch" ).indexTemplateExists( [ template name] )`
* `getInstance( "Client@cbelasticsearch" ).getIndexTemplate( [ template name] )`
* `getInstance( "Client@cbelasticsearch" ).deleteIndexTemplate( [ template name] )`

Note that an index template may not be deleted if it is in use by a data stream. In order to delete it, you must first delete any data streams which use the template or modify the template used in that data stream.


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://cbelasticsearch.ortusbooks.com/indices/managing-indices/templates.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.