How to Use Index Template in Elasticsearch: Syntax and Example

In Elasticsearch, use index templates to define settings and mappings that automatically apply to new indices matching a pattern. Create an index template with PUT _index_template/{template_name} including index_patterns, template settings, and mappings. This helps keep your indices consistent without manual setup each time.

Syntax

An index template in Elasticsearch is created using the PUT _index_template/{template_name} API. It includes:

• template_name: The name you give your template.
• index_patterns: A list of index name patterns this template applies to.
• template: Contains settings and mappings that define how matching indices are created.

json

{
  "index_patterns": ["pattern*"],
  "template": {
    "settings": {
      "number_of_shards": 1
    },
    "mappings": {
      "properties": {
        "field1": { "type": "text" }
      }
    }
  }
}

Example

This example creates an index template named my_template that applies to all indices starting with logs-. It sets one shard and defines a text field called message.

json

PUT _index_template/my_template
{
  "index_patterns": ["logs-*"] ,
  "template": {
    "settings": {
      "number_of_shards": 1
    },
    "mappings": {
      "properties": {
        "message": {
          "type": "text"
        }
      }
    }
  }
}

Output

{
  "acknowledged": true
}

Common Pitfalls

Common mistakes when using index templates include:

• Not matching the index_patterns correctly, so the template does not apply.
• Forgetting to include template wrapper around settings and mappings.
• Using deprecated PUT _template API instead of the newer PUT _index_template.

Always verify your template with a test index creation.

json

PUT _template/old_template
{
  "index_patterns": ["test-*"],
  "settings": {
    "number_of_shards": 1
  },
  "mappings": {
    "properties": {
      "field": { "type": "keyword" }
    }
  }
}

# This is legacy and may not work as expected.

# Correct way:
PUT _index_template/new_template
{
  "index_patterns": ["test-*"] ,
  "template": {
    "settings": {
      "number_of_shards": 1
    },
    "mappings": {
      "properties": {
        "field": { "type": "keyword" }
      }
    }
  }
}

Quick Reference

Term	Description
index_patterns	List of index name patterns the template applies to
template	Object containing settings and mappings for new indices
settings	Index configuration like number of shards and replicas
mappings	Field definitions and data types for the index
PUT _index_template/{name}	API to create or update an index template

Key Takeaways

Use PUT _index_template/{name} to create index templates in Elasticsearch.

Define index_patterns to specify which indices the template applies to.

Include settings and mappings inside the template object for consistent index creation.

Avoid legacy PUT _template API; prefer the newer _index_template API.

Test your template by creating an index that matches the pattern to ensure it applies.