# Background tasks

Use Ibexa Messenger to run processes in the background and conserve system resources.

Some operations in Ibexa DXP don’t have to run immediately when a user clicks a button, for example, re-indexing product prices or processing bulk data. Running such operations in real time could slow down the system and disrupt the user experience.

To solve this, Ibexa DXP provides a package called Ibexa Messenger, which is an overlay to [Symfony Messenger](https://symfony.com/doc/7.4/messenger.html), and it's job is to queue tasks and run them in the background. Ibexa DXP sends messages (or commands) that represent the work to be done later. These messages are stored in a queue and picked up by a background worker, which ensures that resource-heavy tasks are executed at a convenient time, without putting excessive load on the system.

Ibexa Messenger supports multiple storage backends, such as Doctrine, Redis/Valkey, and PostgreSQL, and gives developers the flexibility to create their own message handlers for custom use cases.

## How it works

Ibexa Messenger uses a command bus as a queue that stores messages, or commands, which tell the system what you want to happen, and separates them from the handler, which is the code that actually performs the task.

The process works as follows:

1. A message PHP object is dispatched, for example, `ProductPriceReindex`.
2. The message is wrapped in an envelope, which may contain additional metadata, called [stamps](#stamps).
3. The message is placed in the transport queue. It can be a Doctrine table, a Redis/Valkey queue, and so on.
4. A worker process continuously reads messages from the queue, pulls them into the default bus `ibexa.messenger.bus` and assigns them to the right handler.
5. A handler service processes the message (executes the command). You can register multiple handlers for different jobs.

Here is an example of how you can extend your code and use Ibexa Messenger to process your tasks:

### Configure package

Create a config file, for example, `config/packages/ibexa_messenger.yaml` and define your transport:

```yaml
ibexa_messenger:

    # The DSN of the transport, as expected by Symfony Messenger transport factory.
    transport_dsn:        'doctrine://default?table_name=ibexa_messenger_messages&auto_setup=false'
    deduplication_lock_storage:
        enabled:              true

        # Doctrine DBAL primary connection or custom service
        type:                 doctrine # One of "doctrine"; "custom"; "service"

        # The service ID of a custom Lock Store, if "service" type is selected
        service:              null

        # The DSN of the lock store, if "custom" type is selected
        dsn:                  null
```

> **Note: Supported transports**
>
> You can define different transports: Ibexa Messenger has been tested to work with Redis, MySQL, PostgreSQL. For more information, see [Symfony Messenger documentation](https://symfony.com/doc/current/messenger.html#transports-async-queued-messages) or [Symfony Messenger tutorial](https://symfonycasts.com/screencast/messenger/install).

### Start worker

Use a process manager of your choice to run the following command, or make it start together with the server:

```bash
php bin/console messenger:consume ibexa.messenger.transport --bus=ibexa.messenger.bus --siteaccess=<OPTIONAL>`
```

In [multi-repository setups](https://doc.ibexa.co/en/latest/administration/configuration/repository_configuration/index.md), the worker process always works for a [SiteAccess](https://doc.ibexa.co/en/latest/multisite/multisite_configuration/#siteaccess-configuration) that you indicate by using the `--siteaccess` option, therefore you may need to run multiple workers, one for each SiteAccess.

> **Caution: Multi-repository setups**
>
> Doctrine transport works across multiple repositories without issues, but other transports may need to be adjusted, so that queues across different repositories are not accidentally shared.

#### Configure for production environment

In production, make sure that Ibexa Messenger keeps running. You can configure a process manager, such as [Supervisor](https://symfony.com/doc/7.4/messenger.html#messenger-supervisor) or [systemd](https://symfony.com/doc/7.4/messenger.html#systemd-configuration), to restart the worker if it stops.

To prevent issues with memory leaks or stale processes, run the worker with execution limits:

- `--limit` limits the number of messages the worker processes before exiting.
- `--time-limit` limits the execution time in seconds before the worker exits.
- `--memory-limit` restricts the maximum memory usage.

The following example shows how you can specify these limits:

```bash
php bin/console messenger:consume ibexa.messenger.transport --bus=ibexa.messenger.bus --limit=100 --time-limit=60 --memory-limit=256M
```

For more information, see [Symfony production recommendation for the Messenger component](https://symfony.com/doc/7.4/messenger.html#deploying-to-production).

If you deploy your application on Ibexa Cloud, using [Workers](https://fixed.docs.upsun.com/guides/symfony/workers.html) is recommended.

## Dispatch message

To have a task processed in the background, dispatch an appropriate message by using the `\Symfony\Component\Messenger\MessageBusInterfac\MessageBusInterface::dispatch()` method, exactly as described in [Symfony Messenger documentation](https://symfony.com/doc/7.4/messenger.html#dispatching-the-message):

```php
<?php declare(strict_types=1);

namespace App\Dispatcher;

use Symfony\Component\Messenger\MessageBusInterface;

final readonly class SomeClassThatSchedulesExecutionInTheBackground
{
    public function __construct(
        private MessageBusInterface $bus,
    ) {
    }

    public function schedule(object $message): void
    {
        $this->bus->dispatch($message);
    }
}
```

Additionally, attach message metadata by using [stamps](#stamps).

### Stamps

You can attach [Stamps](https://symfony.com/doc/7.4/messenger.html#envelopes-stamps) to a message envelope to add additional metadata and control how the message is processed.

Use [Stamps available in Symfony](https://github.com/symfony/symfony/tree/7.4/src/Symfony/Component/Messenger/Stamp), and combine them with the ones provided by Ibexa DXP:

- [SudoStamp](#sudostamp)
- [UserPermissionStamp](#userpermissionstamp)

#### SudoStamp

[`SudoStamp`](https://doc.ibexa.co/en/latest/api/php_api/php_api_reference/classes/Ibexa-Contracts-Messenger-Stamp-SudoStamp.html) causes the handler to [use sudo mode](https://doc.ibexa.co/en/latest/api/php_api/php_api/#using-sudo), bypassing all permission checks when processing the message.

It's automatically attached to every dispatched message.

> **Caution: Caution**
>
> Starting with Ibexa DXP 5.0.9, the behavior of automatically attaching a `SudoStamp` to every message is deprecated and will be removed in 6.0. For messages that should be processed without taking permissions into account, always attach the `SudoStamp` manually to keep your code forward-compatible.

The following example shows how you can attach the `SudoStamp` to the message:

```php
use Ibexa\Contracts\Messenger\Stamp\SudoStamp;
use Symfony\Component\Messenger\MessageBusInterface;

$this->bus->dispatch($message, [new SudoStamp()]);
```

#### UserPermissionStamp

[`UserPermissionStamp`](https://doc.ibexa.co/en/latest/api/php_api/php_api_reference/classes/Ibexa-Contracts-Messenger-Stamp-UserPermissionStamp.html) allows you to [set the repository user](https://doc.ibexa.co/en/latest/api/php_api/php_api/#setting-the-repository-user) to process the message. When the user is set, handlers execute actions on their behalf and take their permissions into account.

If you don't attach this stamp, the messages are processed by the default repository user called anonymous user. By combing this stamp with [`SudoStamp`](#sudostamp), you can set the repository user and skip the permission checks at the same time.

The following example shows how you can use `UserPermissionStamp` to preserve the current repository user after the message is dispatched.

```php
use Ibexa\Contracts\Core\Repository\PermissionResolver;
use Ibexa\Contracts\Messenger\Stamp\UserPermissionStamp;
use Symfony\Component\Messenger\MessageBusInterface;

$currentUserId = $this->permissionResolver->getCurrentUserReference()->getUserId();
$this->bus->dispatch($message, [new UserPermissionStamp($currentUserId)]);
```

## Extend Ibexa Messenger

### Register custom message and handler

To handle additional use cases with background tasks, you can create [custom message and handler class](https://symfony.com/doc/7.4/messenger.html#creating-a-message-handler):

```php
<?php declare(strict_types=1);

namespace App\Message;

class SomeMessage
{
    // Add properties and methods as needed for your message.
}
```

```php
<?php declare(strict_types=1);

namespace App\MessageHandler;

use App\Message\SomeMessage;

final class SomeHandler
{
    public function __invoke(SomeMessage $message): void
    {
        // Handle message.
    }
}
```

Add a service definition to `config/services.yaml` and set the `bus` to `ibexa.messenger.bus`:

```yaml
services:
    App\MessageHandler\SomeHandler:
        tags:
            - name: messenger.message_handler
              bus: ibexa.messenger.bus
```