Index templates in Elasticsearch - Step-by-Step Execution

Concept Flow - Index templates

Create or Update Template

↓

Define Index Patterns

↓

Set Settings, Mappings, Aliases

↓

Save Template

↓

New Index Created

↓

Template Matches Index Name?

No→Use Default Settings

Yes↓

Apply Template Settings, Mappings, Aliases

↓

Index Ready for Use

The flow shows how an index template is created and applied automatically to new indices matching its pattern.

Execution Sample

Elasticsearch

PUT _index_template/my_template
{
  "index_patterns": ["logs-*"] ,
  "template": {
    "settings": {"number_of_shards": 1}
  }
}

This creates an index template named 'my_template' that applies to indices starting with 'logs-' and sets shards to 1.

Execution Table

Step	Action	Input/Condition	Result/Output
1	Create template	Name: my_template, Pattern: logs-*	Template stored with pattern logs-*
2	New index creation	Index name: logs-2024-06-01	Check templates matching 'logs-2024-06-01'
3	Match template?	Does 'logs-2024-06-01' match 'logs-*'?	Yes, matches pattern
4	Apply template	Apply settings from 'my_template'	Index created with 1 shard
5	New index creation	Index name: data-2024-06-01	Check templates matching 'data-2024-06-01'
6	Match template?	Does 'data-2024-06-01' match 'logs-*'?	No match
7	Apply default	No matching template	Index created with default settings

💡 Execution stops after index creation with applied template or default settings.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	After Step 6	Final
Template Store	empty	my_template with pattern logs-*	my_template with pattern logs-*	my_template with pattern logs-*	my_template with pattern logs-*	my_template with pattern logs-*
Index Name	none	none	logs-2024-06-01	logs-2024-06-01	data-2024-06-01	data-2024-06-01
Template Match	none	none	true	true	false	false
Index Settings	default	default	applied shards=1	applied shards=1	default	default

Key Moments - 3 Insights

Why does the index 'data-2024-06-01' not get the template settings?

Because its name does not match the template pattern 'logs-*' as shown in execution_table step 6 where the match is false.

Can multiple templates apply to one index?

Yes, but in this example only one template matches. The system applies the best matching template or merges settings if multiple match.

What happens if no template matches an index?

The index is created with default settings, as shown in execution_table step 7 for 'data-2024-06-01'.

Visual Quiz - 3 Questions

Look at the execution_table, what is the shard count for the index 'logs-2024-06-01' after step 4?

A Default shard count

B 1 shard

C 5 shards

D 0 shards

💡 Hint

Check the 'Index Settings' variable in variable_tracker after step 4.

At which step does the index 'data-2024-06-01' fail to match the template pattern?

A Step 3

B Step 5

C Step 6

D Step 7

💡 Hint

Look at the 'Match template?' action and result in execution_table.

If the template pattern was changed to '*-2024-*', which index would match the template?

A Both 'logs-2024-06-01' and 'data-2024-06-01'

B Only 'logs-2024-06-01'

C Only 'data-2024-06-01'

D Neither index

💡 Hint

Consider how the pattern '*-2024-*' matches index names in execution_table steps 2 and 5.

Concept Snapshot

Index templates in Elasticsearch:
- Define patterns to match index names
- Set default settings, mappings, aliases
- Automatically apply when new index matches
- Helps keep index configurations consistent
- No effect on existing indices

Full Transcript

Index templates in Elasticsearch let you define settings and mappings that automatically apply to new indices matching a name pattern. First, you create or update a template with a pattern like 'logs-*'. When a new index is created, Elasticsearch checks if its name matches any template pattern. If yes, it applies the template's settings and mappings to the index. If no template matches, default settings are used. This process ensures new indices have consistent configurations without manual setup each time.