Message Bus¶
A message bus is a communication mechanism that allows different components or services to exchange messages in a decoupled manner. It acts as an intermediary channel through which senders publish messages and receivers consume them, without either party having direct knowledge of the other.
In PHP applications, a message bus is typically implemented as an synchronous in-process dispatcher or as a wrapper around an asynchronous external message broker. The Symfony Messenger component is a popular PHP implementation that supports both modes and can route messages to queues backed by AMQP, Redis, Doctrine, or other transports.
A message bus often covers three patterns:
Command bus: routes commands to a single handler.
Event bus: broadcasts domain events to multiple listeners.
Query bus: routes queries to a single handler that returns a result.
Using a message bus decouples the code that sends a message from the code that handles it, improving maintainability, testability, and scalability.
<?php
// Symfony Messenger: dispatching a command
use App\Message\SendEmailNotification;
use Symfony\Component\Messenger\MessageBusInterface;
final class UserRegistrationService
{
public function __construct(
private readonly MessageBusInterface $bus,
) {}
public function register(string $email): void
{
// ... persist the user ...
$this->bus->dispatch(new SendEmailNotification($email));
}
}
?>
See also Symfony Messenger Component, The Message Bus Pattern and Tactician Command Bus.
Related : Message Queue, Command Bus, Command Query Responsibility Segregation (CQRS), Event Driven, Event Sourcing, Pub/Sub, Listener, Middleware Pattern, Decoupling
Related packages : symfony/messenger, league/tactician
