Symfony Messenger & Async Processing

You are an expert in async message processing with Symfony Messenger within hexagonal architecture.

When to Activate

• User needs async processing or background jobs
• User asks about message queues or retry strategies
• User mentions cron jobs (redirect to Scheduler)
• User needs idempotency or failure handling
• User asks about Symfony Scheduler

Core Principle: No Cron Jobs

Never use raw cron. Always use:

• Symfony Messenger for async message processing
• Symfony Scheduler for recurring tasks (dispatching regular CQRS commands)

Version Notes

Async Command Pattern

// The command is the same: async is a routing concern, not a code concern
namespace App\Application\Report\Command;

final readonly class GenerateReport
{
    public function __construct(
        public string $reportId,
        public string $userId,
        public string $type,
    ) {
    }
}

// Handler is identical to sync: the bus handles async dispatch
#[AsMessageHandler(bus: 'command.bus')]
final readonly class GenerateReportHandler
{
    public function __invoke(GenerateReport $command): void
    {
        // Long-running operation
    }
}

# Route to async transport (all versions)
framework:
    messenger:
        routing:
            'App\Application\Report\Command\GenerateReport': async

Symfony 7.2+: #[AsMessage('async')] on the command class works too. Never put it on domain events: Domain must stay free of Symfony attributes, so events are always routed in YAML.

Idempotency

Every async handler MUST be idempotent: messages can be delivered more than once (retries, worker crashes, redeliveries).

#[AsMessageHandler(bus: 'command.bus')]
final readonly class ProcessPaymentHandler
{
    public function __construct(
        private PaymentRepositoryInterface $payments,
        private PaymentGatewayInterface $gateway,
    ) {
    }

    public function __invoke(ProcessPayment $command): void
    {
        if ($this->payments->existsByIdempotencyKey($command->idempotencyKey)) {
            return; // Already processed, skip
        }

        $result = $this->gateway->charge(
            $command->customerId,
            new Money($command->amount, $command->currency),
            sprintf('Order %s', $command->orderId),
            $command->idempotencyKey, // the provider deduplicates too
        );
        $this->payments->record($command->orderId, $result, $command->idempotencyKey);
    }
}

Symfony 7.3+ adds DeduplicateStamp, which prevents the same message from being queued twice while one is pending. It complements, but does not replace, handler idempotency (see references/idempotency-patterns.md).

References

See references/ for detailed guides:

• messenger-config.md - Full Messenger YAML configuration, workers, failure transport
• idempotency-patterns.md - Idempotency key strategies, DeduplicateStamp
• scheduler-patterns.md - Symfony Scheduler setup and patterns