api: Add Elasticsearch index settings retrieval to application settings

Gerardo Navarrorequested to merge
gitlab-community/gitlab-org/gitlab:571263-gerardo-navarro-api-admin-application-settings-get-elasticsearch-index-settings into master

What does this MR do and why?

This change introduces the ability to retrieve Elasticsearch index settings via the application settings API endpoint (GET /api/v4/application/settings). This is necessary to provide users with access to the configuration of Elasticsearch indices, which is essential for managing search capabilities and ensuring deterministic configuration management.

Technical changes:

  • Added elasticsearch_index_settings method to the ApplicationSetting model that returns ordered index settings via the Elastic::IndexSetting.order_by_name scope
  • Created a new Grape API entity API::Entities::Elastic::IndexSetting to expose index attributes with proper documentation:
    • alias_name - Name of the Elasticsearch index alias
    • number_of_shards - Number of shards for the Elasticsearch index
    • number_of_replicas - Number of replicas for the Elasticsearch index
  • Updated the application setting API entity to include the new index settings in the response when the elastic_search license feature is available

Example API response:

{
  "elasticsearch_index_settings": [
    {
      "alias_name": "gitlab-production",
      "number_of_shards": 5,
      "number_of_replicas": 1
    }
  ]
}

🛠️ with ❤️ at Siemens

References

Screenshots or screen recordings

Not applicable - API-only change with no UI modifications.

How to set up and validate locally

  • Enable the Elasticsearch feature license in your development environment
  • Create some Elasticsearch index settings in the database: 
    # In rails console
Elastic::IndexSetting.create!(alias_name: 'test-index', number_of_shards: 5, number_of_replicas: 1)
  • Make an API request to retrieve application settings: 
    curl --header "PRIVATE-TOKEN: <your_access_token>" \
     "http://localhost:3000/api/v4/application/settings" | jq '.elasticsearch_index_settings'
  • Verify the response includes the elasticsearch_index_settings array with the expected structure

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