Drupal Interview Preparation Guide

1. Difference between Authentication and Authorization

• Authentication verifies who the user is (login using username/password, OAuth, SSO).

• Authorization determines what the authenticated user is allowed to do (permissions like “edit content”, “administer users”).

Authentication comes first, authorization comes after.

2. What is a Service Container in Drupal?

The service container in Drupal is a centralized system that manages reusable objects called services (e.g., database, mail manager, entity manager).

It helps:

• Avoid tight coupling

• Improve testability

• Follow dependency injection principles

Example services:

• entity_type.manager

• database

• logger.factory

3. How to create a custom module in Drupal 8/9?

Steps:

1. Create a folder inside /modules/custom/my_module

2. Add my_module.info.yml

3. (Optional) Add .module, .routing.yml, .services.yml

4. Enable the module using UI or Drush

Example info.yml:

name: My Module
type: module
core_version_requirement: ^8 || ^9 || ^10
package: Custom

4. What are hooks in Drupal?

Hooks are procedural functions that allow modules to alter or extend Drupal’s behavior without modifying core code.

Example:

hook_form_alter()
hook_node_insert()

Hooks are mainly used for:

• Altering forms

• Reacting to entity events

• Modifying data

5. How to create a custom block in Drupal?

Create a Block Plugin:

• Extend BlockBase

• Use @Block annotation

• Implement build() method

Blocks are reusable UI components that can be placed via Block Layout.

6. Difference between a node and a block in Drupal?

7. How to use Drupal’s Entity API?

Drupal Entity API is used to create, load, update, and delete entities.

Example:

$node = \Drupal::entityTypeManager()
  ->getStorage('node')
  ->load($nid);

It provides:

• Unified data handling

• Strong typing

• Field API integration

8. What is a Drupal theme and how to create one?

A Drupal theme controls the presentation layer (HTML, CSS, JS).

Steps:

1. Create /themes/custom/my_theme

2. Add my_theme.info.yml

3. Add Twig templates and libraries

Themes use Twig, not PHP templates.

9. How to implement caching in Drupal?

Drupal supports caching via:

• Page cache

• Dynamic page cache

• Render cache

• Block cache

Key cache metadata:

• Cache tags

• Cache contexts

• Cache max-age

Proper caching improves performance significantly.

10. What are Drupal’s configuration management features?

Drupal uses Config Management (CMI) to:

• Export configuration to YAML

• Import configuration across environments

drush cex
drush cim

Used for:

• Site settings

• Views

• Content types

• Roles and permissions

11. How to create and use custom fields in Drupal?

Fields can be created via:

• UI (Manage fields)

• Code (Field API)

Fields are attached to:

• Content types

• Entities

• Custom entity types

Drupal supports reusable field storage.

12. Difference between Drupal 7 and Drupal 8/9?

13. How to use Views in Drupal?

Views is a query builder UI used to:

• List content

• Build pages, blocks, feeds

Views supports:

• Filters

• Sorting

• Pagination

• Relationships

It eliminates most custom query code.

14. What is the purpose of hook_menu()?

hook_menu() was used in Drupal 7 for:

• Defining routes

• Menu items

• Page callbacks

In Drupal 8+, it is replaced by Routing YAML and Controllers.

15. How to implement multilingual support in Drupal?

Enable modules:

• Language

• Content Translation

• Interface Translation

Drupal supports:

• Content translation

• Configuration translation

• UI translation

Languages can be assigned per entity and field.

16. What are Drupal user roles and permissions?

• Roles group permissions

• Permissions control access to actions

Example roles:

• Anonymous

• Authenticated

• Administrator

Access control is role-based and granular.

17. How to hide a module from the module listing page though it is enabled?

Add in .info.yml:

hidden: true

This keeps the module enabled but hides it from the UI module list.

18. What is a Design Pattern and which design patterns does Drupal use?

A design pattern is a reusable solution to common software problems.

Drupal uses:

• Dependency Injection

• Factory Pattern

• Singleton (limited)

• Observer (Event system)

• Plugin pattern

19. Difference between Cache Tags and Cache Contexts?

20. What is an Event Subscriber in Drupal?

An Event Subscriber listens to Symfony events and executes logic when the event occurs.

Example events:

• Kernel request

• Response

• Entity events

It replaces many hook use cases.

21. Difference between Event Subscriber and Hooks in Drupal?

When to Use Hooks in Drupal

Use Hooks When:

• You need to alter existing Drupal data or behavior

• You are working with forms, entities, or render arrays

• The logic is simple and procedural

• You want quick integration with Drupal core APIs

• Backward compatibility or legacy code is involved

Common Hook Use Cases

• Alter a form

• React when an entity is saved

• Modify a query

• Change render output

22. Explain Drupal Behaviors

Drupal Behaviors attach JavaScript functionality after AJAX or page load.

They ensure JS runs:

• On initial page load

• After AJAX updates

Used instead of document.ready().

23. What is Dependency Injection in Drupal?

Dependency Injection means injecting services instead of calling them statically.

Benefits:

• Testability

• Loose coupling

• Clean architecture

Implemented via constructors.

24. Which DB Engine does Drupal use?

Drupal supports:

• MySQL / MariaDB

• PostgreSQL

• SQLite

It uses Database Abstraction Layer, making DB engine interchangeable.

25. What is SDC in Drupal?

SDC (Single Directory Components) is a Drupal feature that groups:

• Twig

• CSS

• JS

• Metadata

Into one component directory, improving frontend architecture.

26. Why do we use annotations in Drupal?

Annotations are used to:

• Register plugins

• Provide metadata

Example:

• Block plugins

• Queue workers

• Field formatters

They replace manual registration.

27. Why YAML is used instead of TPL files in Drupal?

YAML is used for:

• Configuration

• Routing

• Services

TPL (PHPTemplate) was replaced by Twig, which is safer, cleaner, and more maintainable.

28. How can we defer some configuration to be pushed to respective environments?

By using:

• settings.php overrides

• Environment-specific config splits

• Config Ignore / Config Split modules

Example:

• Dev - enable debug

• Prod - disable debug