Component templates in Elasticsearch

Introduction

Component templates help you reuse settings and mappings for your Elasticsearch indexes. They save time and keep your index setup consistent.

When you want to apply the same settings or mappings to many indexes.

When you need to update common index configurations easily in one place.

When you want to organize index templates into smaller reusable parts.

When managing multiple indexes with similar structures in Elasticsearch.

Syntax

Elasticsearch

{
  "template": {
    "settings": { ... },
    "mappings": { ... },
    "aliases": { ... }
  }
}

The template object contains the settings, mappings, and aliases you want to reuse.

You create component templates separately and then combine them in index templates.

Examples

A simple component template with one shard and a text field called name.

Elasticsearch

{
  "template": {
    "settings": {
      "number_of_shards": 1
    },
    "mappings": {
      "properties": {
        "name": { "type": "text" }
      }
    }
  }
}

A component template that only sets the refresh interval for indexes.

Elasticsearch

{
  "template": {
    "settings": {
      "refresh_interval": "1s"
    }
  }
}

Sample Program

This example creates a component template named my_component_template with 2 replicas and mappings for user and message fields. Then it retrieves the template to show its content.

Elasticsearch

PUT _component_template/my_component_template
{
  "template": {
    "settings": {
      "number_of_replicas": 2
    },
    "mappings": {
      "properties": {
        "user": { "type": "keyword" },
        "message": { "type": "text" }
      }
    }
  }
}

GET _component_template/my_component_template

Important Notes

You can combine multiple component templates into an index template for flexible index creation.

Component templates make it easier to manage large Elasticsearch setups by reusing common parts.

Summary

Component templates store reusable index settings and mappings.

They help keep index configurations consistent and easy to update.

You create component templates separately and then use them in index templates.

Practice

1. What is the main purpose of a component template in Elasticsearch?

easy

A. To manage user access permissions

B. To store actual index data

C. To store reusable index settings and mappings

D. To perform search queries

Solution

1. Step 1: Understand component template role

   Component templates hold reusable parts like settings and mappings for indexes.

2. Step 2: Differentiate from other features

   They do not store data or handle queries or permissions directly.

3. Final Answer:

   To store reusable index settings and mappings -> Option C

4. Quick Check:

   Component templates = reusable settings/mappings [OK]

Hint: Component templates hold reusable settings, not data or queries [OK]

Common Mistakes:

• Confusing component templates with actual index data storage
• Thinking component templates handle search queries
• Assuming component templates manage user permissions

2. Which of the following is the correct way to create a component template using Elasticsearch API?

easy

A. PUT /_component_template/my_template { "template": { "settings": { "number_of_shards": 1 } } }

B. POST /my_template { "settings": { "number_of_shards": 1 } }

C. GET /_component_template/my_template { "settings": { "number_of_shards": 1 } }

D. DELETE /_component_template/my_template

Solution

1. Step 1: Identify correct HTTP method and endpoint

   Creating a component template uses PUT method on /_component_template/{name}.

2. Step 2: Check request body structure

   The body must include a template object with settings or mappings.

3. Final Answer:

   PUT /_component_template/my_template { "template": { "settings": { "number_of_shards": 1 } } } -> Option A

4. Quick Check:

   PUT + /_component_template + template body = A [OK]

Hint: Use PUT with /_component_template and include 'template' in body [OK]

Common Mistakes:

• Using POST instead of PUT for creation
• Using GET or DELETE for creating templates
• Omitting the 'template' wrapper in the JSON body

3. Given this component template creation request, what will be the value of number_of_replicas in the resulting index if used in an index template?

PUT /_component_template/replica_template
{
  "template": {
    "settings": {
      "number_of_replicas": 2
    }
  }
}

medium

A. 2

B. 1

C. 0

D. Undefined

Solution

1. Step 1: Read the component template settings

   The template sets number_of_replicas to 2 explicitly.

2. Step 2: Understand inheritance in index templates

   When this component template is used in an index template, the setting applies to the index.

3. Final Answer:

   2 -> Option A

4. Quick Check:

   Component template sets replicas = 2 [OK]

Hint: Settings in component templates apply directly when used [OK]

Common Mistakes:

• Assuming default replica count 1 overrides component template
• Thinking replicas default to 0 if not set elsewhere
• Confusing component template with index data

4. You tried to create a component template but got an error. Which of these is the most likely cause?

PUT /_component_template/my_template
{
  "settings": {
    "number_of_shards": 3
  }
}

medium

A. Using PUT instead of POST

B. number_of_shards cannot be set in component templates

C. Incorrect endpoint; should be /_index_template

D. Missing the 'template' wrapper around settings

Solution

1. Step 1: Check JSON structure for component template

   Component templates require a template key wrapping settings and mappings.

2. Step 2: Identify missing wrapper

   The request body lacks the "template" object, causing the error.

3. Final Answer:

   Missing the 'template' wrapper around settings -> Option D

4. Quick Check:

   Component template body must have 'template' key [OK]

Hint: Always wrap settings inside 'template' in component templates [OK]

Common Mistakes:

• Omitting the 'template' key in JSON body
• Confusing component template endpoint with index template
• Thinking PUT is wrong method for creation

5. You want to create an index template that uses two component templates: one for settings and one for mappings. Which is the correct way to reference both component templates in the index template?

hard

A. { "index_patterns": ["logs-*"], "template": { "settings": {}, "mappings": {} } }

B. { "index_patterns": ["logs-*"], "composed_of": ["settings_template", "mappings_template"] }

C. { "index_patterns": ["logs-*"], "components": ["settings_template", "mappings_template"] }

D. { "index_patterns": ["logs-*"], "use_components": ["settings_template", "mappings_template"] }

Solution

1. Step 1: Recall index template syntax for component templates

   Index templates use the composed_of array to list component templates.

2. Step 2: Match correct JSON structure

   { "index_patterns": ["logs-*"], "composed_of": ["settings_template", "mappings_template"] } correctly uses composed_of with component template names.

3. Final Answer:

   { "index_patterns": ["logs-*"], "composed_of": ["settings_template", "mappings_template"] } -> Option B

4. Quick Check:

   Use 'composed_of' to combine component templates [OK]

Hint: Use 'composed_of' array to combine component templates [OK]

Common Mistakes:

• Using wrong key like 'components' or 'use_components'
• Trying to put settings and mappings directly instead of referencing components
• Confusing index template syntax with component template syntax