Template priority and composition in Elasticsearch - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this template composition?

Given two index templates with different priorities, what will be the final settings applied to an index named logs-2024?

Elasticsearch

{
  "index_templates": [
    {
      "name": "base_template",
      "index_patterns": ["logs-*"],
      "priority": 10,
      "template": {
        "settings": {
          "number_of_shards": "3",
          "refresh_interval": "30s"
        }
      }
    },
    {
      "name": "override_template",
      "index_patterns": ["logs-2024"],
      "priority": 20,
      "template": {
        "settings": {
          "refresh_interval": "10s",
          "number_of_replicas": "2"
        }
      }
    }
  ]
}

A {"number_of_shards": "3", "refresh_interval": "10s", "number_of_replicas": "2"}

B {"number_of_shards": "3", "refresh_interval": "30s", "number_of_replicas": "2"}

C {"number_of_shards": "3", "refresh_interval": "30s"}

D {"number_of_shards": "3", "refresh_interval": "10s"}

💡 Hint

Remember that templates with higher priority override settings from lower priority templates when index patterns match.

The override_template has a higher priority (20) than base_template (10). Both match the index logs-2024. Settings from the higher priority template override conflicting keys, so refresh_interval becomes "10s" and number_of_replicas is added. The number_of_shards remains from the base template as it is not overridden.

🧠 Conceptual

intermediate

Which template applies when multiple templates match with the same priority?

If two index templates have the same priority and both match an index, which template's settings will Elasticsearch apply?

A The template with the lexicographically larger name is applied first, then the other overrides it.

B Elasticsearch merges both templates, with settings combined and conflicts resolved arbitrarily.

C The template with the lexicographically smaller name is applied first, then the other overrides it.

D Elasticsearch throws an error and refuses to create the index.

💡 Hint

Think about how Elasticsearch resolves conflicts when priorities are equal.

When multiple templates have the same priority and match an index, Elasticsearch applies them in order of their names sorted lexicographically ascending. The later templates override settings from earlier ones.

🔧 Debug

advanced

Why does this template composition not apply the expected settings?

You have two templates: Template A (priority 5) matches logs-* and sets refresh_interval to "30s". Template B (priority 10) matches logs-2024-* and sets refresh_interval to "15s". You create an index named logs-2023-01. The refresh_interval is "30s" instead of "15s". Why?

A Template A has higher priority, so its settings override Template B.

B Elasticsearch only applies one template per index, always the first defined.

C The index name is invalid, so default settings are used.

D Template B does not match the index name <code>logs-2023-01</code>, so only Template A applies.

💡 Hint

Check the index patterns carefully against the index name.

Template B matches indices starting with logs-2024-, but the index is logs-2023-01, so Template B does not apply. Only Template A applies, setting refresh_interval to "30s".

📝 Syntax

advanced

Which template JSON is correctly structured for composition with priority?

Select the valid JSON structure for an index template with priority and settings composition.

A

{
  "index_patterns": ["logs-*"],
  "priority": 15,
  "settings": {
    "number_of_shards": 1
  }
}

B

{
  "index_patterns": ["logs-*"],
  "priority": 15,
  "template": {
    "settings": {
      "number_of_shards": 1
    }
  }
}

C

{
  "index_patterns": ["logs-*"],
  "priority": "high",
  "template": {
    "settings": {
      "number_of_shards": 1
    }
  }
}

D

{
  "index_patterns": "logs-*",
  "priority": "15",
  "template": {
    "settings": {
      "number_of_shards": "1"
    }
  }
}

💡 Hint

Check the data types and nesting of keys carefully.

Option B correctly uses an array for index_patterns, a numeric priority, and nests settings inside template. Option B uses string types incorrectly and index_patterns is not an array. Option B uses a string for priority which must be a number. Option B places settings outside template, which is invalid.

🚀 Application

expert

How many settings keys will the final index have after applying these templates?

You have three templates: 1. Template X: priority 5, matches logs-*, sets refresh_interval and number_of_shards. 2. Template Y: priority 10, matches logs-2024-*, sets number_of_replicas and overrides refresh_interval. 3. Template Z: priority 10, matches logs-2024-*, sets index.lifecycle.name. You create an index named logs-2024-05. How many unique settings keys will the final index have?

A 4

B 3

C 5

D 2

💡 Hint

Count all unique keys from all matching templates, considering overrides.

Template X applies first (priority 5) and sets two keys: refresh_interval and number_of_shards. Templates Y and Z both have priority 10 and match the index, so they apply next in lex order. Template Y sets number_of_replicas and overrides refresh_interval. Template Z adds index.lifecycle.name. The final unique keys are: number_of_shards, refresh_interval, number_of_replicas, and index.lifecycle.name — total 4.