Outbox: events that do not lie

Wed, 07 Jun 2023 20:40:00 +0300

An email confirming an order that does not exist. A colleague showed me this one last week, together with the mirror bug: an order that exists and never got its email.

The code was the obvious kind. Commit the Doctrine transaction, then dispatch to the AMQP transport. Two systems, two writes, no shared transaction. Publish after commit and the process can die between them, event lost. Publish inside the transaction and the broker gets an event for data that may still roll back. Both orders are wrong, and under real load this fires weekly.

Scheduler component, or cron as messages

Wed, 31 May 2023 20:20:00 +0300

crontab -l under a login nobody remembers creating. That is where the real business logic of one server lived: a nightly cleanup, an export, a retry script.

Symfony 6.3 came out yesterday with a Scheduler component. Periodic tasks defined in PHP, executed as Messenger messages. Experimental, but the idea deserves a note.

#[AsSchedule('default')]
final class MainSchedule implements ScheduleProviderInterface
{
    public function getSchedule(): Schedule
    {
        return (new Schedule())->add(
            RecurringMessage::every('10 minutes', new CleanupExpiredCarts()),
        );
    }
}

Then messenger:consume scheduler_default, and a worker fires the messages.

Messenger on Murat Useinov

Outbox: events that do not lie

Scheduler component, or cron as messages