Event Driven Architecture

Quick Introduction

Event Driven Architecture is a single PHP idea you'll use in almost every backend project.

In this lesson you learn only event driven architecture — not five topics at once. By the end you can write a small working example and explain it in an interview.

We connect each lesson to our course projects: Login System, Blog CMS, REST API, Inventory, Employee Management, and E-Commerce Backend.

Business Problem

You're building the E-Commerce Backend. After a user signs in, you need event driven architecture working correctly before storing data or showing a dashboard.

Without understanding Event Driven Architecture, the team ships bugs: wrong totals, broken sessions, or type errors that only appear in production. This lesson fixes that with one clear pattern you can copy into your project today.

Core Concept

• Event Driven Architecture is one focused idea — learn it before mixing with other PHP topics.
• Use it in PHP 8.3+ with declare(strict_types=1); at the top of every file.
• Our course project (E-Commerce Backend) uses event driven architecture in real handlers.
• Run small scripts with php file.php after each change — don't just read.
• Interviewers ask for a one-minute explanation plus a tiny code sample.

Syntax

Core syntax for Event Driven Architecture. Every keyword below appears in production PHP — Laravel and Symfony use the same primitives under the hood.

declare(strict_types=1);

Keywords: declare · strict_types · namespace

Step-by-Step Example

Run this script locally. Change one value, run again, and watch what changes.

<?php
declare(strict_types=1);

namespace Events;

final readonly class OrderPlaced {
    public function __construct(public int $orderId, public int $customerId) {}
}

interface EventBus { public function publish(object $event): void; }

final class SyncEventBus implements EventBus {
    /** @param list<callable> $handlers */
    public function __construct(private array $handlers) {}

    public function publish(object $event): void {
        foreach ($this->handlers as $handler) {
            $handler($event);
        }
    }
}

$bus = new SyncEventBus([
    fn(OrderPlaced $e) => error_log("Send email for order {$e->orderId}"),
    fn(OrderPlaced $e) => error_log("Reserve inventory for order {$e->orderId}"),
]);

$bus->publish(new OrderPlaced(1042, 7));

Line by line

1. — part of the event driven architecture example; run the file to see the result.
2. declare(strict_types=1); — turns on strict type checking for this file.
3. namespace Events; — part of the event driven architecture example; run the file to see the result.
4. final readonly class OrderPlaced { — part of the event driven architecture example; run the file to see the result.
5. public function __construct(public int $orderId, public int $customerId) {} — part of the event driven architecture example; run the file to see the result.

User #42 (user@example.com) balance $19.99

Real-World Example

In the E-Commerce Backend, event driven architecture appears in a single request handler — not spread across ten files. Keep the example small, test it with php, then paste the pattern into your project branch.

<?php
declare(strict_types=1);

// TODO: Event Driven Architecture exercise for E-Commerce Backend