Messenger: Sync & Queued Message Handling

Warning: You are browsing the documentation for Symfony 6.3, which is no longer maintained.

Read the updated version of this page for Symfony 7.2 (the current stable version).

Messenger provides a message bus with the ability to send messages and then handle them immediately in your application or send them through transports (e.g. queues) to be handled later. To learn more deeply about it, read the Messenger component docs.

Installation

In applications using Symfony Flex, run this command to install messenger:

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$ composer require symfony/messenger

Creating a Message & Handler

Messenger centers around two different classes that you'll create: (1) a message class that holds data and (2) a handler(s) class that will be called when that message is dispatched. The handler class will read the message class and perform one or more tasks.

There are no specific requirements for a message class, except that it can be serialized:

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// src/Message/SmsNotification.php
namespace App\Message;

class SmsNotification
{
    public function __construct(
        private string $content,
    ) {
    }

    public function getContent(): string
    {
        return $this->content;
    }
}

A message handler is a PHP callable, the recommended way to create it is to create a class that has the AsMessageHandler attribute and has an __invoke() method that's type-hinted with the message class (or a message interface):

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// src/MessageHandler/SmsNotificationHandler.php
namespace App\MessageHandler;

use App\Message\SmsNotification;
use Symfony\Component\Messenger\Attribute\AsMessageHandler;

#[AsMessageHandler]
class SmsNotificationHandler
{
    public function __invoke(SmsNotification $message)
    {
        // ... do some work - like sending an SMS message!
    }
}

Tip

You can also use the #[AsMessageHandler] attribute on individual class methods. You may use the attribute on as many methods in a single class as you like, allowing you to group the handling of multiple related types of messages.

6.1

Support for #[AsMessageHandler] on methods was introduced in Symfony 6.1.

Thanks to autoconfiguration and the SmsNotification type-hint, Symfony knows that this handler should be called when an SmsNotification message is dispatched. Most of the time, this is all you need to do. But you can also manually configure message handlers. To see all the configured handlers, run:

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$ php bin/console debug:messenger

Dispatching the Message

You're ready! To dispatch the message (and call the handler), inject the messenger.default_bus service (via the MessageBusInterface), like in a controller:

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// src/Controller/DefaultController.php
namespace App\Controller;

use App\Message\SmsNotification;
use Symfony\Bundle\FrameworkBundle\Controller\AbstractController;
use Symfony\Component\HttpFoundation\Response;
use Symfony\Component\Messenger\MessageBusInterface;

class DefaultController extends AbstractController
{
    public function index(MessageBusInterface $bus): Response
    {
        // will cause the SmsNotificationHandler to be called
        $bus->dispatch(new SmsNotification('Look! I created a message!'));

        // ...
    }
}

Transports: Async/Queued Messages

By default, messages are handled as soon as they are dispatched. If you want to handle a message asynchronously, you can configure a transport. A transport is capable of sending messages (e.g. to a queueing system) and then receiving them via a worker. Messenger supports multiple transports.

Note

If you want to use a transport that's not supported, check out the Enqueue's transport, which backs services like Kafka and Google Pub/Sub.

A transport is registered using a "DSN". Thanks to Messenger's Flex recipe, your .env file already has a few examples.

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# MESSENGER_TRANSPORT_DSN=amqp://guest:guest@localhost:5672/%2f/messages
# MESSENGER_TRANSPORT_DSN=doctrine://default
# MESSENGER_TRANSPORT_DSN=redis://localhost:6379/messages

Uncomment whichever transport you want (or set it in .env.local). See Messenger: Sync & Queued Message Handling for more details.

Next, in config/packages/messenger.yaml, let's define a transport called async that uses this configuration:

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# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            async: "%env(MESSENGER_TRANSPORT_DSN)%"

            # or expanded to configure more options
            #async:
            #    dsn: "%env(MESSENGER_TRANSPORT_DSN)%"
            #    options: []

Routing Messages to a Transport

Now that you have a transport configured, instead of handling a message immediately, you can configure them to be sent to a transport:

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# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            async: "%env(MESSENGER_TRANSPORT_DSN)%"

        routing:
            # async is whatever name you gave your transport above
            'App\Message\SmsNotification': async

Thanks to this, the App\Message\SmsNotification will be sent to the async transport and its handler(s) will not be called immediately. Any messages not matched under routing will still be handled immediately, i.e. synchronously.

Note

You may use a partial PHP namespace like 'App\Message\*' to match all the messages within the matching namespace. The only requirement is that the '*' wildcard has to be placed at the end of the namespace.

You may use '*' as the message class. This will act as a default routing rule for any message not matched under routing. This is useful to ensure no message is handled synchronously by default.

The only drawback is that '*' will also apply to the emails sent with the Symfony Mailer (which uses SendEmailMessage when Messenger is available). This could cause issues if your emails are not serializable (e.g. if they include file attachments as PHP resources/streams).

You can also route classes by their parent class or interface. Or send messages to multiple transports:

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# config/packages/messenger.yaml
framework:
    messenger:
        routing:
            # route all messages that extend this example base class or interface
            'App\Message\AbstractAsyncMessage': async
            'App\Message\AsyncMessageInterface': async

            'My\Message\ToBeSentToTwoSenders': [async, audit]

Note

If you configure routing for both a child and parent class, both rules are used. E.g. if you have an SmsNotification object that extends from Notification, both the routing for Notification and SmsNotification will be used.

Tip

You can define and override the transport that a message is using at runtime by using the TransportNamesStamp on the envelope of the message. This stamp takes an array of transport name as its only argument. For more information about stamps, see Envelopes & Stamps.

6.2

The TransportNamesStamp stamp was introduced in Symfony 6.2.

Doctrine Entities in Messages

If you need to pass a Doctrine entity in a message, it's better to pass the entity's primary key (or whatever relevant information the handler actually needs, like email, etc.) instead of the object (otherwise you might see errors related to the Entity Manager):

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// src/Message/NewUserWelcomeEmail.php
namespace App\Message;

class NewUserWelcomeEmail
{
    public function __construct(
        private int $userId,
    ) {
    }

    public function getUserId(): int
    {
        return $this->userId;
    }
}

Then, in your handler, you can query for a fresh object:

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// src/MessageHandler/NewUserWelcomeEmailHandler.php
namespace App\MessageHandler;

use App\Message\NewUserWelcomeEmail;
use App\Repository\UserRepository;
use Symfony\Component\Messenger\Attribute\AsMessageHandler;

#[AsMessageHandler]
class NewUserWelcomeEmailHandler
{
    public function __construct(
        private UserRepository $userRepository,
    ) {
    }

    public function __invoke(NewUserWelcomeEmail $welcomeEmail): void
    {
        $user = $this->userRepository->find($welcomeEmail->getUserId());

        // ... send an email!
    }
}

This guarantees the entity contains fresh data.

Handling Messages Synchronously

If a message doesn't match any routing rules, it won't be sent to any transport and will be handled immediately. In some cases (like when binding handlers to different transports), it's easier or more flexible to handle this explicitly: by creating a sync transport and "sending" messages there to be handled immediately:

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# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            # ... other transports

            sync: 'sync://'

        routing:
            App\Message\SmsNotification: sync

Creating your Own Transport

You can also create your own transport if you need to send or receive messages from something that is not supported. See How to Create Your own Messenger Transport.

Consuming Messages (Running the Worker)

Once your messages have been routed, in most cases, you'll need to "consume" them. You can do this with the messenger:consume command:

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$ php bin/console messenger:consume async

# use -vv to see details about what's happening
$ php bin/console messenger:consume async -vv

The first argument is the receiver's name (or service id if you routed to a custom service). By default, the command will run forever: looking for new messages on your transport and handling them. This command is called your "worker".

Tip

In a development environment and if you're using the Symfony CLI tool, you can configure workers to be automatically run along with the webserver. You can find more information in the Symfony CLI Workers documentation.

Tip

To properly stop a worker, throw an instance of StopWorkerException.

Deploying to Production

On production, there are a few important things to think about:

Use a Process Manager like Supervisor or systemd to keep your worker(s) running
You'll want one or more "workers" running at all times. To do that, use a process control system like Supervisor or systemd.
Don't Let Workers Run Forever
Some services (like Doctrine's EntityManager) will consume more memory over time. So, instead of allowing your worker to run forever, use a flag like messenger:consume --limit=10 to tell your worker to only handle 10 messages before exiting (then the process manager will create a new process). There are also other options like --memory-limit=128M and --time-limit=3600.
Stopping Workers That Encounter Errors
If a worker dependency like your database server is down, or timeout is reached, you can try to add reconnect logic, or just quit the worker if it receives too many errors with the --failure-limit option of the messenger:consume command.
Restart Workers on Deploy
Each time you deploy, you'll need to restart all your worker processes so that they see the newly deployed code. To do this, run messenger:stop-workers on deployment. This will signal to each worker that it should finish the message it's currently handling and should shut down gracefully. Then, the process manager will create new worker processes. The command uses the app cache internally - so make sure this is configured to use an adapter you like.
Use the Same Cache Between Deploys
If your deploy strategy involves the creation of new target directories, you should set a value for the cache.prefix.seed configuration option in order to use the same cache namespace between deployments. Otherwise, the cache.app pool will use the value of the kernel.project_dir parameter as base for the namespace, which will lead to different namespaces each time a new deployment is made.

Prioritized Transports

Sometimes certain types of messages should have a higher priority and be handled before others. To make this possible, you can create multiple transports and route different messages to them. For example:

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# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            async_priority_high:
                dsn: '%env(MESSENGER_TRANSPORT_DSN)%'
                options:
                    # queue_name is specific to the doctrine transport
                    queue_name: high

                    # for AMQP send to a separate exchange then queue
                    #exchange:
                    #    name: high
                    #queues:
                    #    messages_high: ~
                    # for redis try "group"
            async_priority_low:
                dsn: '%env(MESSENGER_TRANSPORT_DSN)%'
                options:
                    queue_name: low

        routing:
            'App\Message\SmsNotification': async_priority_low
            'App\Message\NewUserWelcomeEmail': async_priority_high

You can then run individual workers for each transport or instruct one worker to handle messages in a priority order:

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$ php bin/console messenger:consume async_priority_high async_priority_low

The worker will always first look for messages waiting on async_priority_high. If there are none, then it will consume messages from async_priority_low.

Limit Consuming to Specific Queues

Some transports (notably AMQP) have the concept of exchanges and queues. A Symfony transport is always bound to an exchange. By default, the worker consumes from all queues attached to the exchange of the specified transport. However, there are use cases to want a worker to only consume from specific queues.

You can limit the worker to only process messages from specific queue(s):

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$ php bin/console messenger:consume my_transport --queues=fasttrack

# you can pass the --queues option more than once to process multiple queues
$ php bin/console messenger:consume my_transport --queues=fasttrack1 --queues=fasttrack2

Note

To allow using the queues option, the receiver must implement the QueueReceiverInterface.

Checking the Number of Queued Messages Per Transport

Run the messenger:stats command to know how many messages are in the "queues" of some or all transports:

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# displays the number of queued messages in all transports
$ php bin/console messenger:stats

# shows stats only for some transports
$ php bin/console messenger:stats my_transport_name other_transport_name

Note

In order for this command to work, the configured transport's receiver must implement MessageCountAwareInterface.

6.2

The messenger:stats command was introduced in Symfony 6.2.

Supervisor Configuration

Supervisor is a great tool to guarantee that your worker process(es) is always running (even if it closes due to failure, hitting a message limit or thanks to messenger:stop-workers). You can install it on Ubuntu, for example, via:

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$ sudo apt-get install supervisor

Supervisor configuration files typically live in a /etc/supervisor/conf.d directory. For example, you can create a new messenger-worker.conf file there to make sure that 2 instances of messenger:consume are running at all times:

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;/etc/supervisor/conf.d/messenger-worker.conf
[program:messenger-consume]
command=php /path/to/your/app/bin/console messenger:consume async --time-limit=3600
user=ubuntu
numprocs=2
startsecs=0
autostart=true
autorestart=true
startretries=10
process_name=%(program_name)s_%(process_num)02d

Change the async argument to use the name of your transport (or transports) and user to the Unix user on your server.

Caution

During a deployment, something might be unavailable (e.g. the database) causing the consumer to fail to start. In this situation, Supervisor will try startretries number of times to restart the command. Make sure to change this setting to avoid getting the command in a FATAL state, which will never restart again.

Each restart, Supervisor increases the delay by 1 second. For instance, if the value is 10, it will wait 1 sec, 2 sec, 3 sec, etc. This gives the service a total of 55 seconds to become available again. Increase the startretries setting to cover the maximum expected downtime.

If you use the Redis Transport, note that each worker needs a unique consumer name to avoid the same message being handled by multiple workers. One way to achieve this is to set an environment variable in the Supervisor configuration file, which you can then refer to in messenger.yaml (see the ref:`Redis section <messenger-redis-transport>` below):

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environment=MESSENGER_CONSUMER_NAME=%(program_name)s_%(process_num)02d

Next, tell Supervisor to read your config and start your workers:

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$ sudo supervisorctl reread

$ sudo supervisorctl update

$ sudo supervisorctl start messenger-consume:*

# If you deploy an update of your code, don't forget to restart your workers
# to run the new code
$ sudo supervisorctl restart messenger-consume:*

See the Supervisor docs for more details.

Graceful Shutdown

If you install the PCNTL PHP extension in your project, workers will handle the SIGTERM or SIGINT POSIX signals to finish processing their current message before terminating.

However, you might prefer to use different POSIX signals for graceful shutdown. You can override default ones by setting the framework.messenger.stop_worker_on_signals configuration option.

6.3

The framework.messenger.stop_worker_on_signals option was introduced in Symfony 6.3.

In some cases the SIGTERM signal is sent by Supervisor itself (e.g. stopping a Docker container having Supervisor as its entrypoint). In these cases you need to add a stopwaitsecs key to the program configuration (with a value of the desired grace period in seconds) in order to perform a graceful shutdown:

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[program:x]
stopwaitsecs=20

Systemd Configuration

While Supervisor is a great tool, it has the disadvantage that you need system access to run it. Systemd has become the standard on most Linux distributions, and has a good alternative called user services.

Systemd user service configuration files typically live in a ~/.config/systemd/user directory. For example, you can create a new messenger-worker.service file. Or a messenger-worker@.service file if you want more instances running at the same time:

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[Unit]
Description=Symfony messenger-consume %i

[Service]
ExecStart=php /path/to/your/app/bin/console messenger:consume async --time-limit=3600
Restart=always
RestartSec=30

[Install]
WantedBy=default.target

Now, tell systemd to enable and start one worker:

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$ systemctl --user enable messenger-worker@1.service
$ systemctl --user start messenger-worker@1.service

# to enable and start 20 workers
$ systemctl --user enable messenger-worker@{1..20}.service
$ systemctl --user start messenger-worker@{1..20}.service

If you change your service config file, you need to reload the daemon:

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$ systemctl --user daemon-reload

To restart all your consumers:

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$ systemctl --user restart messenger-consume@*.service

The systemd user instance is only started after the first login of the particular user. Consumer often need to start on system boot instead. Enable lingering on the user to activate that behavior:

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$ loginctl enable-linger <your-username>

Logs are managed by journald and can be worked with using the journalctl command:

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# follow logs of consumer nr 11
$ journalctl -f --user-unit messenger-consume@11.service

# follow logs of all consumers
$ journalctl -f --user-unit messenger-consume@*

# follow all logs from your user services
$ journalctl -f _UID=$UID

See the systemd docs for more details.

Note

You either need elevated privileges for the journalctl command, or add your user to the systemd-journal group:

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$ sudo usermod -a -G systemd-journal <your-username>

Stateless Worker

PHP is designed to be stateless, there are no shared resources across different requests. In HTTP context PHP cleans everything after sending the response, so you can decide to not take care of services that may leak memory.

On the other hand, it's common for workers to process messages sequentially in long-running CLI processes which don't finish after processing a single message. Beware about service states to prevent information and/or memory leakage as Symfony will inject the same instance of a service in all messages, preserving the internal state of the services.

However, certain Symfony services, such as the Monolog fingers crossed handler, leak by design. Symfony provides a service reset feature to solve this problem. When resetting the container automatically between two messages, Symfony looks for any services implementing ResetInterface (including your own services) and calls their reset() method so they can clean their internal state.

If a service is not stateless and you want to reset its properties after each message, then the service must implement ResetInterface where you can reset the properties in the reset() method.

If you don't want to reset the container, add the --no-reset option when running the messenger:consume command.

6.1

In Symfony versions previous to 6.1, the service container didn't reset automatically between messages and you had to set the framework.messenger.reset_on_message option to true.

Rate Limited Transport

6.2

The rate_limiter option was introduced in Symfony 6.2.

Sometimes you might need to rate limit your message worker. You can configure a rate limiter on a transport (requires the RateLimiter component) by setting its rate_limiter option:

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# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            async:
                rate_limiter: your_rate_limiter_name

Caution

When a rate limiter is configured on a transport, it will block the whole worker when the limit is hit. You should make sure you configure a dedicated worker for a rate limited transport to avoid other transports to be blocked.

Retries & Failures

If an exception is thrown while consuming a message from a transport it will automatically be re-sent to the transport to be tried again. By default, a message will be retried 3 times before being discarded or sent to the failure transport. Each retry will also be delayed, in case the failure was due to a temporary issue. All of this is configurable for each transport:

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# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            async_priority_high:
                dsn: '%env(MESSENGER_TRANSPORT_DSN)%'

                # default configuration
                retry_strategy:
                    max_retries: 3
                    # milliseconds delay
                    delay: 1000
                    # causes the delay to be higher before each retry
                    # e.g. 1 second delay, 2 seconds, 4 seconds
                    multiplier: 2
                    max_delay: 0
                    # override all of this with a service that
                    # implements Symfony\Component\Messenger\Retry\RetryStrategyInterface
                    # service: null

Tip

Symfony triggers a WorkerMessageRetriedEvent when a message is retried so you can run your own logic.

Note

Thanks to SerializedMessageStamp, the serialized form of the message is saved, which prevents to serialize it again if the message is later retried.

6.1

The SerializedMessageStamp class was introduced in Symfony 6.1.

Avoiding Retrying

Sometimes handling a message might fail in a way that you know is permanent and should not be retried. If you throw UnrecoverableMessageHandlingException, the message will not be retried.

Forcing Retrying

Sometimes handling a message must fail in a way that you know is temporary and must be retried. If you throw RecoverableMessageHandlingException, the message will always be retried infinitely and max_retries setting will be ignored.

Saving & Retrying Failed Messages

If a message fails it is retried multiple times (max_retries) and then will be discarded. To avoid this happening, you can instead configure a failure_transport:

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# config/packages/messenger.yaml
framework:
    messenger:
        # after retrying, messages will be sent to the "failed" transport
        failure_transport: failed

        transports:
            # ... other transports

            failed: 'doctrine://default?queue_name=failed'

In this example, if handling a message fails 3 times (default max_retries), it will then be sent to the failed transport. While you can use messenger:consume failed to consume this like a normal transport, you'll usually want to manually view the messages in the failure transport and choose to retry them:

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# see all messages in the failure transport with a default limit of 50
$ php bin/console messenger:failed:show

# see the 10 first messages
$ php bin/console messenger:failed:show --max=10

# see only MyClass messages
$ php bin/console messenger:failed:show --class-filter='MyClass'

# see the number of messages by message class
$ php bin/console messenger:failed:show --stats

# see details about a specific failure
$ php bin/console messenger:failed:show 20 -vv

# view and retry messages one-by-one
$ php bin/console messenger:failed:retry -vv

# retry specific messages
$ php bin/console messenger:failed:retry 20 30 --force

# remove a message without retrying it
$ php bin/console messenger:failed:remove 20

# remove messages without retrying them and show each message before removing it
$ php bin/console messenger:failed:remove 20 30 --show-messages

6.2

The --class-filter and --stats options were introduced in Symfony 6.2.

If the message fails again, it will be re-sent back to the failure transport due to the normal retry rules. Once the max retry has been hit, the message will be discarded permanently.

Multiple Failed Transports

Sometimes it is not enough to have a single, global failed transport configured because some messages are more important than others. In those cases, you can override the failure transport for only specific transports:

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# config/packages/messenger.yaml
framework:
    messenger:
        # after retrying, messages will be sent to the "failed" transport
        # by default if no "failed_transport" is configured inside a transport
        failure_transport: failed_default

        transports:
            async_priority_high:
                dsn: '%env(MESSENGER_TRANSPORT_DSN)%'
                failure_transport: failed_high_priority

            # since no failed transport is configured, the one used will be
            # the global "failure_transport" set
            async_priority_low:
                dsn: 'doctrine://default?queue_name=async_priority_low'

            failed_default: 'doctrine://default?queue_name=failed_default'
            failed_high_priority: 'doctrine://default?queue_name=failed_high_priority'

If there is no failure_transport defined globally or on the transport level, the messages will be discarded after the number of retries.

The failed commands have an optional option --transport to specify the failure_transport configured at the transport level.

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# see all messages in "failure_transport" transport
$ php bin/console messenger:failed:show --transport=failure_transport

# retry specific messages from "failure_transport"
$ php bin/console messenger:failed:retry 20 30 --transport=failure_transport --force

# remove a message without retrying it from "failure_transport"
$ php bin/console messenger:failed:remove 20 --transport=failure_transport

Transport Configuration

Messenger supports a number of different transport types, each with their own options. Options can be passed to the transport via a DSN string or configuration.

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# .env
MESSENGER_TRANSPORT_DSN=amqp://localhost/%2f/messages?auto_setup=false
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# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            my_transport:
                dsn: "%env(MESSENGER_TRANSPORT_DSN)%"
                options:
                    auto_setup: false

Options defined under options take precedence over ones defined in the DSN.

AMQP Transport

The AMQP transport uses the AMQP PHP extension to send messages to queues like RabbitMQ. Install it by running:

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$ composer require symfony/amqp-messenger

The AMQP transport DSN may looks like this:

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# .env
MESSENGER_TRANSPORT_DSN=amqp://guest:guest@localhost:5672/%2f/messages

# or use the AMQPS protocol
MESSENGER_TRANSPORT_DSN=amqps://guest:guest@localhost/%2f/messages

If you want to use TLS/SSL encrypted AMQP, you must also provide a CA certificate. Define the certificate path in the amqp.cacert PHP.ini setting (e.g. amqp.cacert = /etc/ssl/certs) or in the cacert parameter of the DSN (e.g amqps://localhost?cacert=/etc/ssl/certs/).

The default port used by TLS/SSL encrypted AMQP is 5671, but you can overwrite it in the port parameter of the DSN (e.g. amqps://localhost?cacert=/etc/ssl/certs/&port=12345).

Note

By default, the transport will automatically create any exchanges, queues and binding keys that are needed. That can be disabled, but some functionality may not work correctly (like delayed queues). To not autocreate any queues, you can configure a transport with queues: [].

Note

You can limit the consumer of an AMQP transport to only process messages from some queues of an exchange. See Messenger: Sync & Queued Message Handling.

The transport has a number of other options, including ways to configure the exchange, queues binding keys and more. See the documentation on Connection.

The transport has a number of options:

Option Description Default
auto_setup Whether the exchanges and queues should be created automatically during send / get. true
cacert Path to the CA cert file in PEM format.  
cert Path to the client certificate in PEM format.  
channel_max Specifies highest channel number that the server permits. 0 means standard extension limit  
confirm_timeout Timeout in seconds for confirmation; if none specified, transport will not wait for message confirmation. Note: 0 or greater seconds. May be fractional.  
connect_timeout Connection timeout. Note: 0 or greater seconds. May be fractional.  
frame_max The largest frame size that the server proposes for the connection, including frame header and end-byte. 0 means standard extension limit (depends on librabbimq default frame size limit)  
heartbeat The delay, in seconds, of the connection heartbeat that the server wants. 0 means the server does not want a heartbeat. Note, librabbitmq has limited heartbeat support, which means heartbeats checked only during blocking calls.  
host Hostname of the AMQP service  
key Path to the client key in PEM format.  
login Username to use to connect the AMQP service  
password Password to use to connect to the AMQP service  
persistent   'false'
port Port of the AMQP service  
read_timeout Timeout in for income activity. Note: 0 or greater seconds. May be fractional.  
retry    
sasl_method    
connection_name For custom connection names (requires at least version 1.10 of the PHP AMQP extension)  
verify Enable or disable peer verification. If peer verification is enabled then the common name in the server certificate must match the server name. Peer verification is enabled by default.  
vhost Virtual Host to use with the AMQP service  
write_timeout Timeout in for outcome activity. Note: 0 or greater seconds. May be fractional.  
delay[queue_name_pattern] Pattern to use to create the queues delay_%exchange_name%_%routing_key%_%delay%
delay[exchange_name] Name of the exchange to be used for the delayed/retried messages delays
queues[name][arguments] Extra arguments  
queues[name][binding_arguments] Arguments to be used while binding the queue.  
queues[name][binding_keys] The binding keys (if any) to bind to this queue  
queues[name][flags] Queue flags AMQP_DURABLE
exchange[arguments] Extra arguments for the exchange (e.g. alternate-exchange)  
exchange[default_publish_routing_key] Routing key to use when publishing, if none is specified on the message  
exchange[flags] Exchange flags AMQP_DURABLE
exchange[name] Name of the exchange  
exchange[type] Type of exchange fanout

6.1

The connection_name option was introduced in Symfony 6.1.

You can also configure AMQP-specific settings on your message by adding AmqpStamp to your Envelope:

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use Symfony\Component\Messenger\Bridge\Amqp\Transport\AmqpStamp;
// ...

$attributes = [];
$bus->dispatch(new SmsNotification(), [
    new AmqpStamp('custom-routing-key', AMQP_NOPARAM, $attributes),
]);

Caution

The consumers do not show up in an admin panel as this transport does not rely on \AmqpQueue::consume() which is blocking. Having a blocking receiver makes the --time-limit/--memory-limit options of the messenger:consume command as well as the messenger:stop-workers command inefficient, as they all rely on the fact that the receiver returns immediately no matter if it finds a message or not. The consume worker is responsible for iterating until it receives a message to handle and/or until one of the stop conditions is reached. Thus, the worker's stop logic cannot be reached if it is stuck in a blocking call.

Tip

If your application faces socket exceptions or high connection churn (shown by the rapid creation and deletion of connections), consider using AMQProxy. This tool works as a gateway between Symfony Messenger and AMQP server, maintaining stable connections and minimizing overheads (which also improves the overall performance).

Doctrine Transport

The Doctrine transport can be used to store messages in a database table. Install it by running:

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$ composer require symfony/doctrine-messenger

The Doctrine transport DSN may looks like this:

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# .env
MESSENGER_TRANSPORT_DSN=doctrine://default

The format is doctrine://<connection_name>, in case you have multiple connections and want to use one other than the "default". The transport will automatically create a table named messenger_messages.

If you want to change the default table name, pass a custom table name in the DSN by using the table_name option:

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# .env
MESSENGER_TRANSPORT_DSN=doctrine://default?table_name=your_custom_table_name

Or, to create the table yourself, set the auto_setup option to false and generate a migration.

Caution

The datetime property of the messages stored in the database uses the timezone of the current system. This may cause issues if multiple machines with different timezone configuration use the same storage.

The transport has a number of options:

Option Description Default
table_name Name of the table messenger_messages
queue_name Name of the queue (a column in the table, to use one table for multiple transports) default
redeliver_timeout Timeout before retrying a message that's in the queue but in the "handling" state (if a worker stopped for some reason, this will occur, eventually you should retry the message) - in seconds. 3600
auto_setup Whether the table should be created automatically during send / get. true

Note

Set redeliver_timeout to a greater value than your slowest message duration. Otherwise, some messages will start a second time while the first one is still being handled.

When using PostgreSQL, you have access to the following options to leverage the LISTEN/NOTIFY feature. This allow for a more performant approach than the default polling behavior of the Doctrine transport because PostgreSQL will directly notify the workers when a new message is inserted in the table.

Option Description Default
use_notify Whether to use LISTEN/NOTIFY. true
check_delayed_interval The interval to check for delayed messages, in milliseconds. Set to 0 to disable checks. 60000
get_notify_timeout The length of time to wait for a response when calling PDO::pgsqlGetNotify, in milliseconds. 0

Beanstalkd Transport

The Beanstalkd transport sends messages directly to a Beanstalkd work queue. Install it by running:

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$ composer require symfony/beanstalkd-messenger

The Beanstalkd transport DSN may looks like this:

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# .env
MESSENGER_TRANSPORT_DSN=beanstalkd://localhost:11300?tube_name=foo&timeout=4&ttr=120

# If no port, it will default to 11300
MESSENGER_TRANSPORT_DSN=beanstalkd://localhost

The transport has a number of options:

Option Description Default
tube_name Name of the queue default
timeout Message reservation timeout - in seconds. 0 (will cause the server to immediately return either a response or a TransportException will be thrown)
ttr The message time to run before it is put back in the ready queue - in seconds. 90

Redis Transport

The Redis transport uses streams to queue messages. This transport requires the Redis PHP extension (>=4.3) and a running Redis server (^5.0). Install it by running:

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$ composer require symfony/redis-messenger

The Redis transport DSN may looks like this:

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# .env
MESSENGER_TRANSPORT_DSN=redis://localhost:6379/messages
# Full DSN Example
MESSENGER_TRANSPORT_DSN=redis://password@localhost:6379/messages/symfony/consumer?auto_setup=true&serializer=1&stream_max_entries=0&dbindex=0
# Redis Cluster Example
MESSENGER_TRANSPORT_DSN=redis://host-01:6379,redis://host-02:6379,redis://host-03:6379,redis://host-04:6379
# Unix Socket Example
MESSENGER_TRANSPORT_DSN=redis:///var/run/redis.sock
# TLS Example
MESSENGER_TRANSPORT_DSN=rediss://localhost:6379/messages

A number of options can be configured via the DSN or via the options key under the transport in messenger.yaml:

Option Description Default
stream The Redis stream name messages
group The Redis consumer group name symfony
consumer Consumer name used in Redis consumer
auto_setup Create the Redis group automatically? true
auth The Redis password  
delete_after_ack If true, messages are deleted automatically after processing them true
delete_after_reject If true, messages are deleted automatically if they are rejected true
lazy Connect only when a connection is really needed false
serializer How to serialize the final payload in Redis (the Redis::OPT_SERIALIZER option) Redis::SERIALIZER_PHP
stream_max_entries The maximum number of entries which the stream will be trimmed to. Set it to a large enough number to avoid losing pending messages 0 (which means "no trimming")
redeliver_timeout Timeout before retrying a pending message which is owned by an abandoned consumer (if a worker died for some reason, this will occur, eventually you should retry the message) - in seconds. 3600
claim_interval Interval on which pending/abandoned messages should be checked for to claim - in milliseconds 60000 (1 Minute)
persistent_id String, if null connection is non-persistent. null
retry_interval Int, value in milliseconds 0
read_timeout Float, value in seconds default indicates unlimited 0
timeout Connection timeout. Float, value in seconds default indicates unlimited 0
sentinel_master String, if null or empty Sentinel support is disabled null

6.1

The persistent_id, retry_interval, read_timeout, timeout, and sentinel_master options were introduced in Symfony 6.1.

Caution

There should never be more than one messenger:consume command running with the same combination of stream, group and consumer, or messages could end up being handled more than once. If you run multiple queue workers, consumer can be set to an environment variable, like %env(MESSENGER_CONSUMER_NAME)%, set by Supervisor (example below) or any other service used to manage the worker processes. In a container environment, the HOSTNAME can be used as the consumer name, since there is only one worker per container/host. If using Kubernetes to orchestrate the containers, consider using a StatefulSet to have stable names.

Tip

Set delete_after_ack to true (if you use a single group) or define stream_max_entries (if you can estimate how many max entries is acceptable in your case) to avoid memory leaks. Otherwise, all messages will remain forever in Redis.

In Memory Transport

The in-memory transport does not actually deliver messages. Instead, it holds them in memory during the request, which can be useful for testing. For example, if you have an async_priority_normal transport, you could override it in the test environment to use this transport:

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# config/packages/test/messenger.yaml
framework:
    messenger:
        transports:
            async_priority_normal: 'in-memory://'

Then, while testing, messages will not be delivered to the real transport. Even better, in a test, you can check that exactly one message was sent during a request:

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// tests/Controller/DefaultControllerTest.php
namespace App\Tests\Controller;

use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;
use Symfony\Component\Messenger\Transport\InMemory\InMemoryTransport;

class DefaultControllerTest extends WebTestCase
{
    public function testSomething(): void
    {
        $client = static::createClient();
        // ...

        $this->assertSame(200, $client->getResponse()->getStatusCode());

        /* @var InMemoryTransport $transport */
        $transport = $this->getContainer()->get('messenger.transport.async_priority_normal');
        $this->assertCount(1, $transport->getSent());
    }
}

6.3

The namespace of the InMemoryTransport class changed in Symfony 6.3 from Symfony\Component\Messenger\Transport\InMemoryTransport to Symfony\Component\Messenger\Transport\InMemory\InMemoryTransport.

The transport has a number of options:

serialize (boolean, default: false)
Whether to serialize messages or not. This is useful to test an additional layer, especially when you use your own message serializer.

Note

All in-memory transports will be reset automatically after each test in test classes extending KernelTestCase or WebTestCase.

Amazon SQS

The Amazon SQS transport is perfect for applications hosted on AWS. Install it by running:

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$ composer require symfony/amazon-sqs-messenger

The SQS transport DSN may looks like this:

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# .env
MESSENGER_TRANSPORT_DSN=https://sqs.eu-west-3.amazonaws.com/123456789012/messages?access_key=AKIAIOSFODNN7EXAMPLE&secret_key=j17M97ffSVoKI0briFoo9a
MESSENGER_TRANSPORT_DSN=sqs://localhost:9494/messages?sslmode=disable

Note

The transport will automatically create queues that are needed. This can be disabled by setting the auto_setup option to false.

Tip

Before sending or receiving a message, Symfony needs to convert the queue name into an AWS queue URL by calling the GetQueueUrl API in AWS. This extra API call can be avoided by providing a DSN which is the queue URL.

The transport has a number of options:

Option Description Default
access_key AWS access key must be urlencoded
account Identifier of the AWS account The owner of the credentials
auto_setup Whether the queue should be created automatically during send / get. true
buffer_size Number of messages to prefetch 9
debug If true it logs all HTTP requests and responses (it impacts performance) false
endpoint Absolute URL to the SQS service https://sqs.eu-west-1.amazonaws.com
poll_timeout Wait for new message duration in seconds 0.1
queue_name Name of the queue messages
region Name of the AWS region eu-west-1
secret_key AWS secret key must be urlencoded
session_token AWS session token  
visibility_timeout Amount of seconds the message will not be visible (Visibility Timeout) Queue's configuration
wait_time Long polling duration in seconds 20

6.1

The session_token option was introduced in Symfony 6.1.

Note

The wait_time parameter defines the maximum duration Amazon SQS should wait until a message is available in a queue before sending a response. It helps reducing the cost of using Amazon SQS by eliminating the number of empty responses.

The poll_timeout parameter defines the duration the receiver should wait before returning null. It avoids blocking other receivers from being called.

Note

If the queue name is suffixed by .fifo, AWS will create a FIFO queue. Use the stamp AmazonSqsFifoStamp to define the Message group ID and the Message deduplication ID.

FIFO queues don't support setting a delay per message, a value of delay: 0 is required in the retry strategy settings.

Serializing Messages

When messages are sent to (and received from) a transport, they're serialized using PHP's native serialize() & unserialize() functions. You can change this globally (or for each transport) to a service that implements SerializerInterface:

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# config/packages/messenger.yaml
framework:
    messenger:
        serializer:
            default_serializer: messenger.transport.symfony_serializer
            symfony_serializer:
                format: json
                context: { }

        transports:
            async_priority_normal:
                dsn: # ...
                serializer: messenger.transport.symfony_serializer

The messenger.transport.symfony_serializer is a built-in service that uses the Serializer component and can be configured in a few ways. If you do choose to use the Symfony serializer, you can control the context on a case-by-case basis via the SerializerStamp (see Envelopes & Stamps).

Tip

When sending/receiving messages to/from another application, you may need more control over the serialization process. Using a custom serializer provides that control. See SymfonyCasts' message serializer tutorial for details.

Getting Results from your Handlers

When a message is handled, the HandleMessageMiddleware adds a HandledStamp for each object that handled the message. You can use this to get the value returned by the handler(s):

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use Symfony\Component\Messenger\MessageBusInterface;
use Symfony\Component\Messenger\Stamp\HandledStamp;

$envelope = $messageBus->dispatch(new SomeMessage());

// get the value that was returned by the last message handler
$handledStamp = $envelope->last(HandledStamp::class);
$handledStamp->getResult();

// or get info about all of handlers
$handledStamps = $envelope->all(HandledStamp::class);

Getting Results when Working with Command & Query Buses

The Messenger component can be used in CQRS architectures where command & query buses are central pieces of the application. Read Martin Fowler's article about CQRS to learn more and how to configure multiple buses.

As queries are usually synchronous and expected to be handled once, getting the result from the handler is a common need.

A HandleTrait exists to get the result of the handler when processing synchronously. It also ensures that exactly one handler is registered. The HandleTrait can be used in any class that has a $messageBus property:

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// src/Action/ListItems.php
namespace App\Action;

use App\Message\ListItemsQuery;
use App\MessageHandler\ListItemsQueryResult;
use Symfony\Component\Messenger\HandleTrait;
use Symfony\Component\Messenger\MessageBusInterface;

class ListItems
{
    use HandleTrait;

    public function __construct(
        private MessageBusInterface $messageBus,
    ) {
    }

    public function __invoke(): void
    {
        $result = $this->query(new ListItemsQuery(/* ... */));

        // Do something with the result
        // ...
    }

    // Creating such a method is optional, but allows type-hinting the result
    private function query(ListItemsQuery $query): ListItemsQueryResult
    {
        return $this->handle($query);
    }
}

Hence, you can use the trait to create command & query bus classes. For example, you could create a special QueryBus class and inject it wherever you need a query bus behavior instead of the MessageBusInterface:

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// src/MessageBus/QueryBus.php
namespace App\MessageBus;

use Symfony\Component\Messenger\Envelope;
use Symfony\Component\Messenger\HandleTrait;
use Symfony\Component\Messenger\MessageBusInterface;

class QueryBus
{
    use HandleTrait;

    public function __construct(
        private MessageBusInterface $messageBus,
    ) {
    }

    /**
     * @param object|Envelope $query
     *
     * @return mixed The handler returned value
     */
    public function query($query): mixed
    {
        return $this->handle($query);
    }
}

Customizing Handlers

Configuring Handlers Using Attributes

You can configure your handler by passing options to the attribute:

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// src/MessageHandler/SmsNotificationHandler.php
namespace App\MessageHandler;

use App\Message\OtherSmsNotification;
use App\Message\SmsNotification;
use Symfony\Component\Messenger\Attribute\AsMessageHandler;

#[AsMessageHandler(fromTransport: 'async', priority: 10)]
class SmsNotificationHandler
{
    public function __invoke(SmsNotification $message): void
    {
        // ...
    }
}

Possible options to configure with the attribute are:

Option Description
bus Name of the bus from which the handler can receive messages, by default all buses.
fromTransport Name of the transport from which the handler can receive messages, by default all transports.
handles Type of messages (FQCN) that can be processed by the handler, only needed if can't be guessed by type-hint.
method Name of the method that will process the message, only if the target is a class.
priority Priority of the handler when multiple handlers can process the same message.

Manually Configuring Handlers

Symfony will normally find and register your handler automatically. But, you can also configure a handler manually - and pass it some extra config - by tagging the handler service with messenger.message_handler

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# config/services.yaml
services:
    App\MessageHandler\SmsNotificationHandler:
        tags: [messenger.message_handler]

        # or configure with options
        tags:
            -
                name: messenger.message_handler
                # only needed if can't be guessed by type-hint
                handles: App\Message\SmsNotification

Possible options to configure with tags are:

Option Description
bus Name of the bus from which the handler can receive messages, by default all buses.
from_transport Name of the transport from which the handler can receive messages, by default all transports.
handles Type of messages (FQCN) that can be processed by the handler, only needed if can't be guessed by type-hint.
method Name of the method that will process the message.
priority Priority of the handler when multiple handlers can process the same message.

Handling Multiple Messages

A single handler class can handle multiple messages. For that add the #AsMessageHandler attribute to all the handling methods:

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// src/MessageHandler/SmsNotificationHandler.php
namespace App\MessageHandler;

use App\Message\OtherSmsNotification;
use App\Message\SmsNotification;

class SmsNotificationHandler
{
    #[AsMessageHandler]
    public function handleSmsNotification(SmsNotification $message): void
    {
        // ...
    }

    #[AsMessageHandler]
    public function handleOtherSmsNotification(OtherSmsNotification $message): void
    {
        // ...
    }
}

6.2

Implementing the MessageSubscriberInterface is another way to handle multiple messages with one handler class. This interface was deprecated in Symfony 6.2.

Transactional Messages: Handle New Messages After Handling is Done

A message handler can dispatch new messages while handling others, to either the same or a different bus (if the application has multiple buses). Any errors or exceptions that occur during this process can have unintended consequences, such as:

  1. If using the DoctrineTransactionMiddleware and a dispatched message throws an exception, then any database transactions in the original handler will be rolled back.
  2. If the message is dispatched to a different bus, then the dispatched message will be handled even if some code later in the current handler throws an exception.

An Example RegisterUser Process

Consider an application with both a command and an event bus. The application dispatches a command named RegisterUser to the command bus. The command is handled by the RegisterUserHandler which creates a User object, stores that object to a database and dispatches a UserRegistered message to the event bus.

There are many handlers to the UserRegistered message, one handler may send a welcome email to the new user. We are using the DoctrineTransactionMiddleware to wrap all database queries in one database transaction.

Problem 1: If an exception is thrown when sending the welcome email, then the user will not be created because the DoctrineTransactionMiddleware will rollback the Doctrine transaction, in which the user has been created.

Problem 2: If an exception is thrown when saving the user to the database, the welcome email is still sent because it is handled asynchronously.

DispatchAfterCurrentBusMiddleware Middleware

For many applications, the desired behavior is to only handle messages that are dispatched by a handler once that handler has fully finished. This can be done by using the DispatchAfterCurrentBusMiddleware and adding a DispatchAfterCurrentBusStamp stamp to the message Envelope:

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// src/Messenger/CommandHandler/RegisterUserHandler.php
namespace App\Messenger\CommandHandler;

use App\Entity\User;
use App\Messenger\Command\RegisterUser;
use App\Messenger\Event\UserRegistered;
use Doctrine\ORM\EntityManagerInterface;
use Symfony\Component\Messenger\Envelope;
use Symfony\Component\Messenger\MessageBusInterface;
use Symfony\Component\Messenger\Stamp\DispatchAfterCurrentBusStamp;

class RegisterUserHandler
{
    public function __construct(
        private MessageBusInterface $eventBus,
        private EntityManagerInterface $em,
    ) {
    }

    public function __invoke(RegisterUser $command): void
    {
        $user = new User($command->getUuid(), $command->getName(), $command->getEmail());
        $this->em->persist($user);

        // The DispatchAfterCurrentBusStamp marks the event message to be handled
        // only if this handler does not throw an exception.

        $event = new UserRegistered($command->getUuid());
        $this->eventBus->dispatch(
            (new Envelope($event))
                ->with(new DispatchAfterCurrentBusStamp())
        );

        // ...
    }
}
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// src/Messenger/EventSubscriber/WhenUserRegisteredThenSendWelcomeEmail.php
namespace App\Messenger\EventSubscriber;

use App\Entity\User;
use App\Messenger\Event\UserRegistered;
use Doctrine\ORM\EntityManagerInterface;
use Symfony\Component\Mailer\MailerInterface;
use Symfony\Component\Mime\RawMessage;

class WhenUserRegisteredThenSendWelcomeEmail
{
    public function __construct(
        private MailerInterface $mailer,
        EntityManagerInterface $em,
    ) {
    }

    public function __invoke(UserRegistered $event): void
    {
        $user = $this->em->getRepository(User::class)->find($event->getUuid());

        $this->mailer->send(new RawMessage('Welcome '.$user->getFirstName()));
    }
}

This means that the UserRegistered message would not be handled until after the RegisterUserHandler had completed and the new User was persisted to the database. If the RegisterUserHandler encounters an exception, the UserRegistered event will never be handled. And if an exception is thrown while sending the welcome email, the Doctrine transaction will not be rolled back.

Note

If WhenUserRegisteredThenSendWelcomeEmail throws an exception, that exception will be wrapped into a DelayedMessageHandlingException. Using DelayedMessageHandlingException::getExceptions will give you all exceptions that are thrown while handling a message with the DispatchAfterCurrentBusStamp.

The dispatch_after_current_bus middleware is enabled by default. If you're configuring your middleware manually, be sure to register dispatch_after_current_bus before doctrine_transaction in the middleware chain. Also, the dispatch_after_current_bus middleware must be loaded for all of the buses being used.

Binding Handlers to Different Transports

Each message can have multiple handlers, and when a message is consumed all of its handlers are called. But you can also configure a handler to only be called when it's received from a specific transport. This allows you to have a single message where each handler is called by a different "worker" that's consuming a different transport.

Suppose you have an UploadedImage message with two handlers:

  • ThumbnailUploadedImageHandler: you want this to be handled by a transport called image_transport
  • NotifyAboutNewUploadedImageHandler: you want this to be handled by a transport called async_priority_normal

To do this, add the from_transport option to each handler. For example:

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// src/MessageHandler/ThumbnailUploadedImageHandler.php
namespace App\MessageHandler;

use App\Message\UploadedImage;

#[AsMessageHandler(fromTransport: 'image_transport')]
class ThumbnailUploadedImageHandler
{
    public function __invoke(UploadedImage $uploadedImage): void
    {
        // do some thumbnailing
    }
}

And similarly:

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// src/MessageHandler/NotifyAboutNewUploadedImageHandler.php
// ...

#[AsMessageHandler(fromTransport: 'async_priority_normal')]
class NotifyAboutNewUploadedImageHandler
{
    // ...
}

Then, make sure to "route" your message to both transports:

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# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            async_priority_normal: # ...
            image_transport: # ...

        routing:
            # ...
            'App\Message\UploadedImage': [image_transport, async_priority_normal]

That's it! You can now consume each transport:

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# will only call ThumbnailUploadedImageHandler when handling the message
$ php bin/console messenger:consume image_transport -vv

$ php bin/console messenger:consume async_priority_normal -vv

Caution

If a handler does not have from_transport config, it will be executed on every transport that the message is received from.

Process Messages by Batches

You can declare "special" handlers which will process messages by batch. By doing so, the handler will wait for a certain amount of messages to be pending before processing them. The declaration of a batch handler is done by implementing BatchHandlerInterface. The BatchHandlerTrait is also provided in order to ease the declaration of these special handlers:

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use Symfony\Component\Messenger\Handler\Acknowledger;
use Symfony\Component\Messenger\Handler\BatchHandlerInterface;
use Symfony\Component\Messenger\Handler\BatchHandlerTrait;

class MyBatchHandler implements BatchHandlerInterface
{
    use BatchHandlerTrait;

    public function __invoke(MyMessage $message, Acknowledger $ack = null): mixed
    {
        return $this->handle($message, $ack);
    }

    private function process(array $jobs): void
    {
        foreach ($jobs as [$message, $ack]) {
            try {
                // Compute $result from $message...

                // Acknowledge the processing of the message
                $ack->ack($result);
            } catch (\Throwable $e) {
                $ack->nack($e);
            }
        }
    }

    // Optionally, you can either redefine the `shouldFlush()` method
    // of the trait to define your own batch size...
    private function shouldFlush(): bool
    {
        return 100 <= \count($this->jobs);
    }

    // ... or redefine the `getBatchSize()` method if the default
    // flush behavior suits your needs
    private function getBatchSize(): int
    {
        return 100;
    }
}

6.3

The getBatchSize() method was introduced in Symfony 6.3.

Note

When the $ack argument of __invoke() is null, the message is expected to be handled synchronously. Otherwise, __invoke() is expected to return the number of pending messages. The BatchHandlerTrait handles this for you.

Note

By default, pending batches are flushed when the worker is idle as well as when it is stopped.

Extending Messenger

Envelopes & Stamps

A message can be any PHP object. Sometimes, you may need to configure something extra about the message - like the way it should be handled inside AMQP or adding a delay before the message should be handled. You can do that by adding a "stamp" to your message:

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use Symfony\Component\Messenger\Envelope;
use Symfony\Component\Messenger\MessageBusInterface;
use Symfony\Component\Messenger\Stamp\DelayStamp;

public function index(MessageBusInterface $bus): void
{
    $bus->dispatch(new SmsNotification('...'), [
        // wait 5 seconds before processing
        new DelayStamp(5000),
    ]);

    // or explicitly create an Envelope
    $bus->dispatch(new Envelope(new SmsNotification('...'), [
        new DelayStamp(5000),
    ]));

    // ...
}

Internally, each message is wrapped in an Envelope, which holds the message and stamps. You can create this manually or allow the message bus to do it. There are a variety of different stamps for different purposes and they're used internally to track information about a message - like the message bus that's handling it or if it's being retried after failure.

Middleware

What happens when you dispatch a message to a message bus depends on its collection of middleware and their order. By default, the middleware configured for each bus looks like this:

  1. add_bus_name_stamp_middleware - adds a stamp to record which bus this message was dispatched into;
  2. dispatch_after_current_bus- see Messenger: Sync & Queued Message Handling;
  3. failed_message_processing_middleware - processes messages that are being retried via the failure transport to make them properly function as if they were being received from their original transport;
  4. Your own collection of middleware;
  5. send_message - if routing is configured for the transport, this sends messages to that transport and stops the middleware chain;
  6. handle_message - calls the message handler(s) for the given message.

Note

These middleware names are actually shortcut names. The real service ids are prefixed with messenger.middleware. (e.g. messenger.middleware.handle_message).

The middleware are executed when the message is dispatched but also again when a message is received via the worker (for messages that were sent to a transport to be handled asynchronously). Keep this in mind if you create your own middleware.

You can add your own middleware to this list, or completely disable the default middleware and only include your own.

If a middleware service is abstract, you can configure its constructor's arguments and a different instance will be created per bus.

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# config/packages/messenger.yaml
framework:
    messenger:
        buses:
            messenger.bus.default:
                # disable the default middleware
                default_middleware: false

                middleware:
                    # use and configure parts of the default middleware you want
                    - 'add_bus_name_stamp_middleware': ['messenger.bus.default']

                    # add your own services that implement Symfony\Component\Messenger\Middleware\MiddlewareInterface
                    - 'App\Middleware\MyMiddleware'
                    - 'App\Middleware\AnotherMiddleware'

Middleware for Doctrine

If you use Doctrine in your app, a number of optional middleware exist that you may want to use:

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# config/packages/messenger.yaml
framework:
    messenger:
        buses:
            command_bus:
                middleware:
                    # each time a message is handled, the Doctrine connection
                    # is "pinged" and reconnected if it's closed. Useful
                    # if your workers run for a long time and the database
                    # connection is sometimes lost
                    - doctrine_ping_connection

                    # After handling, the Doctrine connection is closed,
                    # which can free up database connections in a worker,
                    # instead of keeping them open forever
                    - doctrine_close_connection

                    # logs an error when a Doctrine transaction was opened but not closed
                    - doctrine_open_transaction_logger

                    # wraps all handlers in a single Doctrine transaction
                    # handlers do not need to call flush() and an error
                    # in any handler will cause a rollback
                    - doctrine_transaction

                    # or pass a different entity manager to any
                    #- doctrine_transaction: ['custom']

Other Middlewares

Add the router_context middleware if you need to generate absolute URLs in the consumer (e.g. render a template with links). This middleware stores the original request context (i.e. the host, the HTTP port, etc.) which is needed when building absolute URLs.

Add the validation middleware if you need to validate the message object using the Validator component before handling it. If validation fails, a ValidationFailedException will be thrown. The ValidationStamp can be used to configure the validation groups.

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# config/packages/messenger.yaml
framework:
    messenger:
        buses:
            command_bus:
                middleware:
                    - router_context
                    - validation

Messenger Events

In addition to middleware, Messenger also dispatches several events. You can create an event listener to hook into various parts of the process. For each, the event class is the event name:

6.2

The WorkerRateLimitedEvent was introduced in Symfony 6.2.

Additional Handler Arguments

It's possible to have messenger pass additional data to the message handler using the HandlerArgumentsStamp. Add this stamp to the envelope in a middleware and fill it with any additional data you want to have available in the handler:

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// src/Messenger/AdditionalArgumentMiddleware.php
namespace App\Messenger;

use Symfony\Component\Messenger\Envelope;
use Symfony\Component\Messenger\Middleware\MiddlewareInterface;
use Symfony\Component\Messenger\Middleware\StackInterface;
use Symfony\Component\Messenger\Stamp\HandlerArgumentsStamp;

final class AdditionalArgumentMiddleware implements MiddlewareInterface
{
    public function handle(Envelope $envelope, StackInterface $stack): Envelope
    {
        $envelope = $envelope->with(new HandlerArgumentsStamp([
            $this->resolveAdditionalArgument($envelope->getMessage()),
        ]));

        return $stack->next()->handle($envelope, $stack);
    }

    private function resolveAdditionalArgument(object $message): mixed
    {
        // ...
    }
}

Then your handler will look like this:

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// src/MessageHandler/SmsNotificationHandler.php
namespace App\MessageHandler;

use App\Message\SmsNotification;

final class SmsNotificationHandler
{
    public function __invoke(SmsNotification $message, mixed $additionalArgument)
    {
        // ...
    }
}

6.2

The HandlerArgumentsStamp was introduced in Symfony 6.2.

Message Serializer For Custom Data Formats

If you receive messages from other applications, it's possible that they are not exactly in the format you need. Not all applications will return a JSON message with body and headers fields. In those cases, you'll need to create a new message serializer implementing the SerializerInterface. Let's say you want to create a message decoder:

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namespace App\Messenger\Serializer;

use Symfony\Component\Messenger\Envelope;
use Symfony\Component\Messenger\Transport\Serialization\SerializerInterface;

class MessageWithTokenDecoder implements SerializerInterface
{
    public function decode(array $encodedEnvelope): Envelope
    {
        $envelope = \json_decode($encodedEnvelope, true);

        try {
            // parse the data you received with your custom fields
            $data = $envelope['data'];
            $data['token'] = $envelope['token'];

            // other operations like getting information from stamps
        } catch (\Throwable $throwable) {
            // wrap any exception that may occur in the envelope to send it to the failure transport
            return new Envelope($throwable);
        }

        return new Envelope($data);
    }

    public function encode(Envelope $envelope): array
    {
        // this decoder does not encode messages, but you can implement it by returning
        // an array with serialized stamps if you need to send messages in a custom format
        throw new \LogicException('This serializer is only used for decoding messages.');
    }
}

The next step is to tell Symfony to use this serializer in one or more of your transports:

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# config/packages/messenger.yaml
framework:
    messenger:
        transports:
            my_transport:
                dsn: '%env(MY_TRANSPORT_DSN)%'
                serializer: 'App\Messenger\Serializer\MessageWithTokenDecoder'

Multiple Buses, Command & Event Buses

Messenger gives you a single message bus service by default. But, you can configure as many as you want, creating "command", "query" or "event" buses and controlling their middleware.

A common architecture when building applications is to separate commands from queries. Commands are actions that do something and queries fetch data. This is called CQRS (Command Query Responsibility Segregation). See Martin Fowler's article about CQRS to learn more. This architecture could be used together with the Messenger component by defining multiple buses.

A command bus is a little different from a query bus. For example, command buses usually don't provide any results and query buses are rarely asynchronous. You can configure these buses and their rules by using middleware.

It might also be a good idea to separate actions from reactions by introducing an event bus. The event bus could have zero or more subscribers.

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framework:
    messenger:
        # The bus that is going to be injected when injecting MessageBusInterface
        default_bus: command.bus
        buses:
            command.bus:
                middleware:
                    - validation
                    - doctrine_transaction
            query.bus:
                middleware:
                    - validation
            event.bus:
                default_middleware:
                    enabled: true
                    # set "allow_no_handlers" to true (default is false) to allow having
                    # no handler configured for this bus without throwing an exception
                    allow_no_handlers: false
                    # set "allow_no_senders" to false (default is true) to throw an exception
                    # if no sender is configured for this bus
                    allow_no_senders: true
                middleware:
                    - validation

6.2

The allow_no_senders option was introduced in Symfony 6.2.

This will create three new services:

  • command.bus: autowireable with the MessageBusInterface type-hint (because this is the default_bus);
  • query.bus: autowireable with MessageBusInterface $queryBus;
  • event.bus: autowireable with MessageBusInterface $eventBus.

Restrict Handlers per Bus

By default, each handler will be available to handle messages on all of your buses. To prevent dispatching a message to the wrong bus without an error, you can restrict each handler to a specific bus using the messenger.message_handler tag:

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# config/services.yaml
services:
    App\MessageHandler\SomeCommandHandler:
        tags: [{ name: messenger.message_handler, bus: command.bus }]
        # prevent handlers from being registered twice (or you can remove
        # the MessageHandlerInterface that autoconfigure uses to find handlers)
        autoconfigure: false

This way, the App\MessageHandler\SomeCommandHandler handler will only be known by the command.bus bus.

You can also automatically add this tag to a number of classes by using the _instanceof service configuration. Using this, you can determine the message bus based on an implemented interface:

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# config/services.yaml
services:
    # ...

    _instanceof:
        # all services implementing the CommandHandlerInterface
        # will be registered on the command.bus bus
        App\MessageHandler\CommandHandlerInterface:
            tags:
                - { name: messenger.message_handler, bus: command.bus }

        # while those implementing QueryHandlerInterface will be
        # registered on the query.bus bus
        App\MessageHandler\QueryHandlerInterface:
            tags:
                - { name: messenger.message_handler, bus: query.bus }

Debugging the Buses

The debug:messenger command lists available messages & handlers per bus. You can also restrict the list to a specific bus by providing its name as an argument.

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$ php bin/console debug:messenger

  Messenger
  =========

  command.bus
  -----------

   The following messages can be dispatched:

   ---------------------------------------------------------------------------------------
    App\Message\DummyCommand
        handled by App\MessageHandler\DummyCommandHandler
    App\Message\MultipleBusesMessage
        handled by App\MessageHandler\MultipleBusesMessageHandler
   ---------------------------------------------------------------------------------------

  query.bus
  ---------

   The following messages can be dispatched:

   ---------------------------------------------------------------------------------------
    App\Message\DummyQuery
        handled by App\MessageHandler\DummyQueryHandler
    App\Message\MultipleBusesMessage
        handled by App\MessageHandler\MultipleBusesMessageHandler
   ---------------------------------------------------------------------------------------

Tip

The command will also show the PHPDoc description of the message and handler classes.

Redispatching a Message

It you want to redispatch a message (using the same transport and envelope), create a new RedispatchMessage and dispatch it through your bus. Reusing the same SmsNotification example shown earlier:

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// src/MessageHandler/SmsNotificationHandler.php
namespace App\MessageHandler;

use App\Message\SmsNotification;
use Symfony\Component\Messenger\Attribute\AsMessageHandler;
use Symfony\Component\Messenger\Message\RedispatchMessage;
use Symfony\Component\Messenger\MessageBusInterface;

#[AsMessageHandler]
class SmsNotificationHandler
{
    public function __construct(private MessageBusInterface $bus)
    {
    }

    public function __invoke(SmsNotification $message): void
    {
        // do something with the message
        // then redispatch it based on your own logic

        if ($needsRedispatch) {
            $this->bus->dispatch(new RedispatchMessage($message));
        }
    }
}

The built-in RedispatchMessageHandler will take care of this message to redispatch it through the same bus it was dispatched at first. You can also use the second argument of the RedispatchMessage constructor to provide transports to use when redispatching the message.

6.3

The RedispatchMessage and RedispatchMessageHandler classes were introduced in Symfony 6.3.

Learn more

This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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