Scheduler

Installation

In applications using Symfony Flex, run this command to install the scheduler component:

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$ composer require symfony/scheduler

Symfony Scheduler Basics

The main benefit of using this component is that automation is managed by your application, which gives you a lot of flexibility that is not possible with cron jobs (e.g. dynamic schedules based on certain conditions).

At its core, the Scheduler component allows you to create a task (called a message) that is executed by a service and repeated on some schedule. It has some similarities with the Symfony Messenger component (such as message, handler, bus, transport, etc.), but the main difference is that Messenger can't deal with repetitive tasks at regular intervals.

Consider the following example of an application that sends some reports to customers on a scheduled basis. First, create a Scheduler message that represents the task of creating a report:

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// src/Scheduler/Message/SendDailySalesReports.php
namespace App\Scheduler\Message;

class SendDailySalesReports
{
    public function __construct(private int $id) {}

    public function getId(): int
    {
        return $this->id;
    }
}

Next, create the handler that processes that kind of message:

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// src/Scheduler/Handler/SendDailySalesReportsHandler.php
namespace App\Scheduler\Handler;

use App\Scheduler\Message\SendDailySalesReports;
use Symfony\Component\Messenger\Attribute\AsMessageHandler;

#[AsMessageHandler]
class SendDailySalesReportsHandler
{
    public function __invoke(SendDailySalesReports $message)
    {
        // ... do some work to send the report to the customers
    }
}

Instead of sending these messages immediately (as in the Messenger component), the goal is to create them based on a predefined frequency. This is possible thanks to SchedulerTransport, a special transport for Scheduler messages.

The transport generates, autonomously, various messages according to the assigned frequencies. The following images illustrate the differences between the processing of messages in Messenger and Scheduler components:

In Messenger:

In Scheduler:

Another important difference is that messages in the Scheduler component are recurring. They are represented via the RecurringMessage class.

Attaching Recurring Messages to a Schedule

The configuration of the message frequency is stored in a class that implements ScheduleProviderInterface. This provider uses the method getSchedule() to return a schedule containing the different recurring messages.

The AsSchedule attribute, which by default references the schedule named default, allows you to register on a particular schedule:

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// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

use Symfony\Component\Scheduler\Attribute\AsSchedule;
use Symfony\Component\Scheduler\Schedule;
use Symfony\Component\Scheduler\ScheduleProviderInterface;

#[AsSchedule]
class SaleTaskProvider implements ScheduleProviderInterface
{
    public function getSchedule(): Schedule
    {
        // ...
    }
}

Scheduling Recurring Messages

A RecurringMessage is a message associated with a trigger, which configures the frequency of the message. Symfony provides different types of triggers:

CronExpressionTrigger

A trigger that uses the same syntax as the cron command-line utility.

CallbackTrigger

A trigger that uses a callback to determine the next run date.

ExcludeTimeTrigger

A trigger that excludes certain times from a given trigger.

JitterTrigger

A trigger that adds a random jitter to a given trigger. The jitter is some time that it's added/subtracted to the original triggering date/time. This allows to distribute the load of the scheduled tasks instead of running them all at the exact same time.

PeriodicalTrigger

A trigger that uses a DateInterval to determine the next run date.

Most of them can be created via the RecurringMessage class, as shown in the following examples.

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composer require dragonmantank/cron-expression

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RecurringMessage::cron('* * * * *', new Message());

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RecurringMessage::cron('@daily', new Message());

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RecurringMessage::cron('#midnight', new Message());

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RecurringMessage::every('10 seconds', new Message());
RecurringMessage::every('3 weeks', new Message());
RecurringMessage::every('first Monday of next month', new Message());

$from = new \DateTimeImmutable('13:47', new \DateTimeZone('Europe/Paris'));
$until = '2023-06-12';
RecurringMessage::every('first Monday of next month', new Message(), $from, $until);

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// src/Scheduler/Trigger/NewUserWelcomeEmailHandler.php
namespace App\Scheduler\Trigger;

class ExcludeHolidaysTrigger implements TriggerInterface
{
    public function __construct(private TriggerInterface $inner)
    {
    }

    // use this method to give a nice displayable name to
    // identify your trigger (it eases debugging)
    public function __toString(): string
    {
        return $this->inner.' (except holidays)';
    }

    public function getNextRunDate(\DateTimeImmutable $run): ?\DateTimeImmutable
    {
        if (!$nextRun = $this->inner->getNextRunDate($run)) {
            return null;
        }

        // loop until you get the next run date that is not a holiday
        while (!$this->isHoliday($nextRun) {
            $nextRun = $this->inner->getNextRunDate($nextRun);
        }

        return $nextRun;
    }

    private function isHoliday(\DateTimeImmutable $timestamp): bool
    {
        // add some logic to determine if the given $timestamp is a holiday
        // return true if holiday, false otherwise
    }
}

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RecurringMessage::trigger(
    new ExcludeHolidaysTrigger(
        CronExpressionTrigger::fromSpec('@daily'),
    ),
    new SendDailySalesReports('...'),
);

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// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

#[AsSchedule('uptoyou')]
class SaleTaskProvider implements ScheduleProviderInterface
{
    public function getSchedule(): Schedule
    {
        return $this->schedule ??= (new Schedule())
            ->with(
                RecurringMessage::trigger(
                    new ExcludeHolidaysTrigger(
                        CronExpressionTrigger::fromSpec('@daily'),
                    ),
                    new SendDailySalesReports()
                ),
                RecurringMessage::cron('3 8 * * 1', new CleanUpOldSalesReport())
            );
    }
}

Consuming Messages (Running the Worker)

After defining and attaching your recurring messages to a schedule, you'll need a mechanism to generate and consume the messages according to their defined frequencies. To do that, the Scheduler component uses the messenger:consume command from the Messenger component:

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$ php bin/console messenger:consume scheduler_nameofyourschedule

# use -vv if you need details about what's happening
$ php bin/console messenger:consume scheduler_nameofyourschedule -vv

Debugging the Schedule

The debug:scheduler command provides a list of schedules along with their recurring messages. You can narrow down the list to a specific schedule:

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$ php bin/console debug:scheduler

  Scheduler
  =========

  default
  -------

    ------------------- ------------------------- ----------------------
    Trigger             Provider                  Next Run
    ------------------- ------------------------- ----------------------
    every 2 days        App\Messenger\Foo(0:17..)  Sun, 03 Dec 2023 ...
    15 4 */3 * *        App\Messenger\Foo(0:17..)  Mon, 18 Dec 2023 ...
   -------------------- -------------------------- ---------------------

Efficient management with Symfony Scheduler

When a worker is restarted or undergoes shutdown for a period, the Scheduler transport won't be able to generate the messages (because they are created on-the-fly by the scheduler transport). This implies that any messages scheduled to be sent during the worker's inactive period are not sent, and the Scheduler will lose track of the last processed message. Upon restart, it will recalculate the messages to be generated from that point onward.

To illustrate, consider a recurring message set to be sent every 3 days. If a worker is restarted on day 2, the message will be sent 3 days from the restart, on day 5.

While this behavior may not necessarily pose a problem, there is a possibility that it may not align with what you are seeking.

That's why the scheduler allows to remember the last execution date of a message via the stateful option (and the Cache component). This allows the system to retain the state of the schedule, ensuring that when a worker is restarted, it resumes from the point it left off:

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// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

#[AsSchedule('uptoyou')]
class SaleTaskProvider implements ScheduleProviderInterface
{
    public function getSchedule(): Schedule
    {
        $this->removeOldReports = RecurringMessage::cron('3 8 * * 1', new CleanUpOldSalesReport());

        return $this->schedule ??= (new Schedule())
            ->with(
                // ...
            )
            ->stateful($this->cache)
    }
}

To scale your schedules more effectively, you can use multiple workers. In such cases, a good practice is to add a lock to prevent the same task more than once:

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// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

#[AsSchedule('uptoyou')]
class SaleTaskProvider implements ScheduleProviderInterface
{
    public function getSchedule(): Schedule
    {
        $this->removeOldReports = RecurringMessage::cron('3 8 * * 1', new CleanUpOldSalesReport());

        return $this->schedule ??= (new Schedule())
            ->with(
                // ...
            )
            ->lock($this->lockFactory->createLock('my-lock')
    }
}

Additionally, for better scaling of your schedules, you have the option to wrap your message in a RedispatchMessage. This allows you to specify a transport on which your message will be redispatched before being further redispatched to its corresponding handler:

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// src/Scheduler/SaleTaskProvider.php
namespace App\Scheduler;

#[AsSchedule('uptoyou')]
class SaleTaskProvider implements ScheduleProviderInterface
{
    public function getSchedule(): Schedule
    {
        return $this->schedule ??= (new Schedule())
            ->with(
                RecurringMessage::every('5 seconds'),
                new RedispatchMessage(new Message(), 'async')
            );
    }
}