Magento 2 Architecture for Developers: Modules, DI, and Events
Magento 2 is a powerful but complex e-commerce platform. Understanding its architecture will save you time and help you build extensions that are upgrade-safe and maintainable.
Modules as building blocks
Everything in Magento 2 is organized into modules. A custom module usually lives under app/code/Vendor/Module and has at least a registration.php file and a etc/module.xml configuration file.
<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="urn:magento:framework:Module/etc/module.xsd">
<module name="Vendor_Module" setup_version="1.0.0"/>
</config>
Dependency Injection (DI)
Magento 2 uses a dependency injection container instead of manually creating objects with new. You configure preferences and virtual types in etc/di.xml so that the framework can resolve dependencies.
- Constructor injection is the default: dependencies are passed into a class via its constructor.
- Preferences let you swap one implementation for another.
- Plugins (interceptors) can modify behavior before, after, or around method calls.
Events and observers
Magento 2 ships with an extensive event system. Core code dispatches events (for example, sales_order_place_after), and your module can listen for them with observers defined in events.xml.
This pattern lets you hook into business processes without modifying core files.
Front-end vs back-end areas
Magento distinguishes between:
- frontend – The customer-facing store.
- adminhtml – The admin panel.
Each area can have its own layout XML, JS, and CSS. Be sure to place configuration files in the correct area to avoid unexpected behavior.
Best practices
- Never edit core Magento or vendor files; always extend via modules.
- Use DI and plugins instead of rewriting classes whenever possible.
- Keep modules focused on a single responsibility (for example, payment, shipping, analytics).
Once you understand modules, DI, and events, the rest of Magento 2’s architecture becomes far easier to navigate.
