# Backend

The Chamilo 2.0 backend is built on Symfony 6.4 with Doctrine ORM and API Platform.

* [**Symfony Architecture**](https://docs.chamilo.org/2.x/developer-guide/developer-guide/backend/symfony-architecture) — Bundles, services, and the overall backend structure
* [**Entities and Doctrine**](https://docs.chamilo.org/2.x/developer-guide/developer-guide/backend/entities-and-doctrine) — The 314 entity classes and how they relate
* [**Resource System**](https://docs.chamilo.org/2.x/developer-guide/developer-guide/backend/resource-system) — The ResourceNode/ResourceFile abstraction (key architectural concept)
* [**Controllers**](https://docs.chamilo.org/2.x/developer-guide/developer-guide/backend/controllers) — Controller organization and routing patterns
* [**Events and Listeners**](https://docs.chamilo.org/2.x/developer-guide/developer-guide/backend/events-and-listeners) — How Chamilo uses the Symfony event system
* [**Settings System**](https://docs.chamilo.org/2.x/developer-guide/developer-guide/backend/settings-system) — The 43 settings schemas and how platform configuration works