Component templates in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of creating a component template with settings

What is the output of this Elasticsearch API call when creating a component template named my_template with a number_of_shards setting of 3?

Elasticsearch

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

A {"acknowledged":true}

B {"error":"component_template_already_exists_exception"}

C {"acknowledged":false}

D {"error":"invalid_template_settings"}

💡 Hint

Creating a new component template returns an acknowledged true response if successful.

When you create a component template successfully, Elasticsearch responds with {"acknowledged":true}. Errors occur if the template exists or settings are invalid.

❓ Predict Output

intermediate

Result of applying a component template to an index template

Given a component template comp_temp that sets number_of_replicas to 2, what will be the number_of_replicas setting of an index created from an index template that uses this component template?

Elasticsearch

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

PUT _index_template/my_index_template
{
  "index_patterns": ["myindex*"],
  "composed_of": ["comp_temp"]
}

PUT myindex1

A 0

B 1

C Undefined (error)

D 2

💡 Hint

Component templates settings are merged into index templates and applied to indices.

The component template sets number_of_replicas to 2, so the index created from the index template that uses it will have number_of_replicas = 2.

🔧 Debug

advanced

Identify the error in this component template definition

What error will this component template creation request produce?

Elasticsearch

PUT _component_template/bad_template
{
  "template": {
    "mappings": {
      "properties": {
        "name": { "type": "text" },
        "age": { "type": "integer" }
      }
    },
    "settings": {
      "number_of_shards": "two"
    }
  }
}

A No error, template created successfully

B ValidationException: number_of_shards must be an integer

C ParsingException: unknown field 'mappings' in template

D ElasticsearchTimeoutException

💡 Hint

Check the type of the number_of_shards setting value.

The number_of_shards setting must be an integer, but here it is a string "two", causing a validation error.

🧠 Conceptual

advanced

Understanding component template composition order

If an index template composes two component templates, compA and compB, and both define the refresh_interval setting differently, which value will the index use?

A The value from the index template itself, ignoring component templates

B The value from the first component template listed in the composed_of array

C The value from the last component template listed in the composed_of array

D Elasticsearch throws a conflict error and refuses to create the index

💡 Hint

Later component templates override earlier ones in the composition order.

When multiple component templates define the same setting, the last one in the composed_of list overrides earlier ones.

❓ Predict Output

expert

Output of retrieving a non-existent component template

What is the output of this request when the component template missing_template does not exist?

Elasticsearch

GET _component_template/missing_template

A {"error":{"root_cause":[{"type":"resource_not_found_exception","reason":"component_template [missing_template] missing"}],"type":"resource_not_found_exception","reason":"component_template [missing_template] missing"},"status":404}

B {"component_templates":[]}

C {"acknowledged":false}

D {"error":"index_not_found_exception"}

💡 Hint

Elasticsearch returns a 404 error with details if the component template is missing.

Requesting a non-existent component template returns a 404 resource_not_found_exception error with a descriptive message.

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