Chapter 1: Developing for Drupal 9

Drupal is a web-based Content Management System (CMS). While it is useful out of the box, it is designed with developers in mind. The purpose of this book is to explain how Drupal can be extended in many ways and for many purposes. To this end, the version we will use will be the latest one at the time of writing this book—Drupal 9.

In this book, we will cover a wide range of development topics. We'll discuss how to create a Drupal 9 module, and as we go through the chapters, we'll cover many concepts and tips that will help you build what you need. The goal is not only to explain how things work but also to go through some examples in order to demonstrate them. Since no book can contain everything, I hope that after reading this book, you'll be able to expand on your knowledge on your own using the resources I reference and by looking into the Drupal core code itself. As helpful as such a book can be for learning any kind of software development, if you really want to progress, you will need to apply the knowledge you learned and explore the source code yourself. Only by doing this will you be able to understand complex systems with many dependencies and layers.

This chapter introduces the terminology, tools, and processes for developing modules in Drupal 9. While subsequent chapters focus on code, this chapter focuses on concepts. We'll talk about the architecture of Drupal and how you can hook into Drupal at strategic places to extend it to accomplish new tasks.

The following are the major topics we will be covering in this chapter:

• An introduction to Drupal development
• How did we get to Drupal 9?
• Drupal 9 architecture
• The major subsystems of Drupal
• Tools for developing in Drupal

By the end of this chapter, you will understand the architectural aspects of Drupal and be ready to start writing code.