Component templates in Elasticsearch - Step-by-Step Execution

Concept Flow - Component templates

Define component template

↓

Specify settings, mappings, aliases

↓

Save component template

↓

Use component template in index template

↓

Create index matching template

↓

Index created with combined settings/mappings

Component templates are reusable building blocks for index templates, defining settings, mappings, or aliases that can be shared across multiple index templates.

Execution Sample

Elasticsearch

PUT _component_template/my_template
{
  "template": {
    "settings": {"number_of_shards": 1},
    "mappings": {"properties": {"field1": {"type": "keyword"}}}
  }
}

This code creates a component template named 'my_template' with shard settings and a keyword field mapping.

Execution Table

Step	Action	Request Sent	Response	Resulting State
1	Define component template 'my_template'	PUT _component_template/my_template with settings and mappings	Acknowledged: true	Component template 'my_template' stored
2	Create index template using component template	PUT _index_template/my_index_template with component_templates: ['my_template']	Acknowledged: true	Index template 'my_index_template' references 'my_template'
3	Create index matching template pattern	PUT my-index-000001	Acknowledged: true	Index created with settings and mappings from 'my_template'
4	Verify index settings and mappings	GET my-index-000001/_settings and _mapping	Settings and mappings include number_of_shards=1 and field1 as keyword	Index uses combined template settings

💡 Index created successfully using component template settings and mappings

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
component_template 'my_template'	undefined	{"template":{"settings":{"number_of_shards":1},"mappings":{"properties":{"field1":{"type":"keyword"}}}}}	unchanged	unchanged	unchanged
index_template 'my_index_template'	undefined	undefined	{"component_templates":["my_template"]}	unchanged	unchanged
index 'my-index-000001'	undefined	undefined	undefined	created with settings and mappings from 'my_template'	exists with correct settings and mappings

Key Moments - 2 Insights

Why do we create a component template separately before using it in an index template?

Because component templates are reusable parts that can be shared by multiple index templates, defining them separately allows consistent settings and mappings across indexes. See execution_table step 1 and 2.

What happens if the index name does not match the index template pattern?

The index will not use the component template settings because the index template won't apply. This is why in step 3 the index name must match the pattern defined in the index template.

Visual Quiz - 3 Questions

Look at the execution_table, what is the response after defining the component template?

A Error: template not found

B Acknowledged: true

C Acknowledged: false

D No response

💡 Hint

Check execution_table row 1, Response column

At which step is the index created using the component template?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at execution_table, Step column and Action describing index creation

If we change the component template's number_of_shards to 3, what changes in variable_tracker after Step 1?

A component_template 'my_template' settings show number_of_shards=3

B index_template changes to number_of_shards=3

C index 'my-index-000001' is created with 1 shard

D No change anywhere

💡 Hint

Check variable_tracker row for component_template after Step 1

Concept Snapshot

Component templates define reusable settings, mappings, and aliases.
They are created with PUT _component_template/{name}.
Index templates reference component templates by name.
When an index matches the index template pattern, it inherits combined settings.
This promotes reuse and consistency across indexes.

Full Transcript

Component templates in Elasticsearch are reusable parts that hold settings, mappings, or aliases. First, you create a component template with a PUT request including these definitions. Then, you create an index template that references this component template by name. When you create an index matching the index template's pattern, Elasticsearch applies the combined settings and mappings from the component template. This process helps keep your index configurations consistent and easy to manage. The execution steps show defining the component template, linking it in an index template, creating an index, and verifying the applied settings.