druid/docs/design/indexing-service.md

id	title
indexing-service	Indexing Service

The Apache Druid indexing service is a highly-available, distributed service that runs indexing related tasks.

Indexing tasks are responsible for creating and killing Druid segments.

The indexing service is composed of three main components: Peons that can run a single task, MiddleManagers that manage Peons, and an Overlord that manages task distribution to MiddleManagers. Overlords and MiddleManagers may run on the same process or across multiple processes, while MiddleManagers and Peons always run on the same process.

Tasks are managed using API endpoints on the Overlord service. See Overlord Task API for more information.

Overlord

See Overlord.

Middle Managers

See Middle Manager.

Peons

See Peon.

Tasks

See Tasks.