Messenger: Sync & Queued Message Handling

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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
{
    private $content;

    public function __construct(string $content)
    {
        $this->content = $content;
    }

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

5.4

The #[AsMessageHandler] PHP attribute was introduced in Symfony 5.4. PHP attributes require at least PHP 8.0.

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!
    }
}

Note

You can also create a class without the attribute (e.g. if you're using PHP 7.4), by implementing MessageHandlerInterface instead.

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\Messenger\MessageBusInterface;

class DefaultController extends AbstractController
{
    public function index(MessageBusInterface $bus)
    {
        // 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 '*' 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.

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
{
    private $userId;

    public function __construct(int $userId)
    {
        $this->userId = $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
{
    private $userRepository;

    public function __construct(UserRepository $userRepository)
    {
        $this->userRepository = $userRepository;
    }

    public function __invoke(NewUserWelcomeEmail $welcomeEmail)
    {
        $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.

5.4

The StopWorkerException class was introduced in Symfony 5.4.

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

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

5.3

Limiting the worker to specific queues was introduced in Symfony 5.3.

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 Redis section 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 POSIX signal to finish processing their current message before terminating.

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, workers usually sequentially process messages in long-running CLI processes, which don't finish after processing a single message. That's why you must be careful about service states to prevent information and/or memory leakage.

However, certain Symfony services, such as the Monolog fingers crossed handler, leak by design. In those cases, use the reset_on_message transport option to automatically reset the service container between two messages:

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

5.4

The reset_on_message option was introduced in Symfony 5.4.

Note

reset_on_message will default to true (with no other allowed value) in Symfony 6. To disable this behavior, execute the messenger:consume command with the --no-reset option.

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.

5.2

The WorkerMessageRetriedEvent class was introduced in Symfony 5.2.

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

5.1

The RecoverableMessageHandlingException was introduced in Symfony 5.1.

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
$ php bin/console messenger:failed:show

# 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

5.1

The --show-messages option was introduced in Symfony 5.1.

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

5.3

The possibility to use multiple failed transports was introduced in Symfony 5.3.

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.

5.1

Starting from Symfony 5.1, the AMQP transport has moved to a separate package. 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

5.2

The AMQPS protocol support was introduced in Symfony 5.2.

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

With Symfony 5.3 or newer, 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  
prefetch_count    
read_timeout Timeout in for income activity. Note: 0 or greater seconds. May be fractional.  
retry    
sasl_method    
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

5.2

The confirm_timeout option was introduced in Symfony 5.2.

5.3

The prefetch_count option was deprecated in Symfony 5.3 because it has no effect on the AMQP Messenger transport.

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.

Doctrine Transport

The Doctrine transport can be used to store messages in a database table.

5.1

Starting from Symfony 5.1, the Doctrine transport has moved to a separate package. 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.

5.1

The ability to automatically generate a migration for the messenger_messages table was introduced in Symfony 5.1 and DoctrineBundle 2.1.

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.

5.1

The ability to leverage PostgreSQL's LISTEN/NOTIFY was introduced in Symfony 5.1.

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

5.2

The Beanstalkd transport was introduced in Symfony 5.2.

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).

5.1

Starting from Symfony 5.1, the Redis transport has moved to a separate package. 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&delete_after_ack=true
# 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

5.1

The Unix socket DSN was introduced in Symfony 5.1.

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 false
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)

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.

5.1

The delete_after_ack, redeliver_timeout and claim_interval options were introduced in Symfony 5.1.

5.2

The delete_after_reject and lazy options were introduced in Symfony 5.2.

5.3

The rediss:// DSN scheme support for TLS protocol was introduced in Symfony 5.3.

5.3

The tls option was deprecated in Symfony 5.3, use rediss:// DSN scheme for TLS support instead.

5.4

Not setting a explicit value for the delete_after_ack option is deprecated since Symfony 5.4. In Symfony 6.0, the default value of this option changes from false to true.

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\InMemoryTransport;

class DefaultControllerTest extends WebTestCase
{
    public function testSomething()
    {
        $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());
    }
}

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.

5.3

The serialize option was introduced in Symfony 5.3.

Note

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

Amazon SQS

5.1

The Amazon SQS transport was introduced in Symfony 5.1.

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.

5.2

The feature to provide the queue URL in the DSN was introduced in Symfony 5.2.

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
visibility_timeout Amount of seconds the message will not be visible (Visibility Timeout) Queue's configuration
wait_time Long polling duration in seconds 20

5.3

The debug option was introduced in Symfony 5.3.

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.

Customizing Handlers

Configuring Handlers Using Attributes

5.4

The #[AsMessageHandler] PHP attribute was introduced in Symfony 5.4. PHP attributes require at least PHP 8.0.

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)
    {
        // ...
    }
}

Possible options to configure with the attribute are:

  • bus
  • fromTransport
  • handles
  • method
  • priority

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:

  • bus
  • from_transport
  • handles
  • method
  • priority

Handler Subscriber & Options

A handler class can handle multiple messages or configure itself by implementing MessageSubscriberInterface:

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

use App\Message\OtherSmsNotification;
use App\Message\SmsNotification;
use Symfony\Component\Messenger\Handler\MessageSubscriberInterface;

class SmsNotificationHandler implements MessageSubscriberInterface
{
    public function __invoke(SmsNotification $message)
    {
        // ...
    }

    public function handleOtherSmsNotification(OtherSmsNotification $message)
    {
        // ...
    }

    public static function getHandledMessages(): iterable
    {
        // handle this message on __invoke
        yield SmsNotification::class;

        // also handle this message on handleOtherSmsNotification
        yield OtherSmsNotification::class => [
            'method' => 'handleOtherSmsNotification',
            //'priority' => 0,
            //'bus' => 'messenger.bus.default',
        ];
    }
}

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;
use Symfony\Component\Messenger\Handler\MessageSubscriberInterface;

class ThumbnailUploadedImageHandler implements MessageSubscriberInterface
{
    public function __invoke(UploadedImage $uploadedImage)
    {
        // do some thumbnailing
    }

    public static function getHandledMessages(): iterable
    {
        yield UploadedImage::class => [
            'from_transport' => 'image_transport',
        ];
    }
}

And similarly:

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

class NotifyAboutNewUploadedImageHandler implements MessageSubscriberInterface
{
    // ...

    public static function getHandledMessages(): iterable
    {
        yield UploadedImage::class => [
            'from_transport' => 'async_priority_normal',
        ];
    }
}

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

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.

5.4

BatchHandlerInterface and BatchHandlerTrait were introduced in Symfony 5.4.

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)
{
    // wait 5 seconds before processing
    $bus->dispatch(new SmsNotification('...'), [
        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 Transactional Messages: Handle New Messages After Handling is Done;
  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

                    # 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

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

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

5.4

The doctrine_open_transaction_logger middleware was introduced in Symfony 5.4.

Other Middlewares

5.3

The router_context middleware was introduced in Symfony 5.3.

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:

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
    {
        try {
            // parse the data you received with your custom fields
            $data = $encodedEnvelope['data'];
            $data['token'] = $encodedEnvelope['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. See Multiple Buses.

Learn more

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