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Bridge to use Symfony Messenger on AWS Lambda with Bref.

This bridge allows messages to be dispatched to SQS, SNS or EventBridge, while workers handle those messages on AWS Lambda.

Installation

This guide assumes that:

• Symfony is installed
• Symfony Messenger is installed
• Bref is installed and configured to deploy Symfony

First, install this package:

Next, register the bundle in config/bundles.php:

SQS, SNS and EventBridge can now be used with Symfony Messenger.

Usage

Symfony Messenger dispatches messages. To create a message, follow the Symfony Messenger documentation.

To configure where messages are dispatched, all the examples in this documentation are based on the example from the Symfony documentation:

SQS

The SQS service is a queue that works similar to RabbitMQ. To use it, set its URL in the environment variable MESSENGER_TRANSPORT_DSN:

That's it, messages will be dispatched to that queue.

The implementation uses the SQS transport provided by Symfony Amazon SQS Messenger, so all those features are supported. If you already use that transport, the transition to AWS Lamdba is very easy and should not require any change for dispatching messages.

Create the SQS queue

You can create the Queue yourself in the Console, write custom Cloudformation or use Lift's Queue construct that will handle that for you.

Here is a simple example with Lift, make sure to install the plugin first and check out the full documentation for more details.

In all cases, you would want to disable auto_setup to avoid extra requests and permission issues.

Add permissions

When running Symfony on AWS Lambda, it is not necessary to configure credentials. The AWS client will read them from environment variables automatically.

You just have to provide the correct role statements in serverless.yml and Lambda will take care of the rest. The required IAM permission to publish to SQS using Messenger is sqs:SendMessage on the given queue.

If you use Lift, this is done automatically for you.

Consume messages from SQS

1. If you don't use Lift, create the function that will be invoked by SQS in serverless.yml:

2. Create the handler script (for example bin/consumer.php):

If you are using Symfony 5.1 or later, use this instead:

3. Register and configure the SqsConsumer service:

Now, anytime a message is dispatched to SQS, the Lambda function will be called. The Bref consumer class will put back the message into Symfony Messenger to be processed.

FIFO Queue

The FIFO queue guarantees exactly once delivery, and has a mandatory queue name suffix .fifo:

Symfony Amazon SQS Messenger will automatically calculate/set the MessageGroupId and MessageDeduplicationId parameters required for FIFO queues, but you can set them explicitly:

Everything else is identical to the normal SQS queue.

SNS

AWS SNS is "notification" instead of "queues". Messages may not arrive in the same order as sent, and they might arrive all at once. To use it, create a SNS topic and set it as the DSN:

That's it, messages will be dispatched to that topic.

Note: when running Symfony on AWS Lambda, it is not necessary to configure credentials. The AWS client will read them from environment variables automatically.

To consume messages from SNS:

1. Create the function that will be invoked by SNS in serverless.yml:

2. Create the handler script (for example bin/consumer.php):

If you are using Symfony 5.1 or later, use this instead:

3. Register and configure the SnsConsumer service:

Now, anytime a message is dispatched to SNS, the Lambda function will be called. The Bref consumer class will put back the message into Symfony Messenger to be processed.

EventBridge

AWS EventBridge is a message routing service. It is similar to SNS, but more powerful. To use it, configure the DSN like so:

Optionally you can add set the EventBusName via a event_bus_name query parameter, either the name or the ARN:

That's it, messages will be dispatched to EventBridge.

Note: when running Symfony on AWS Lambda, it is not necessary to configure credentials. The AWS client will read them from environment variables automatically.

To consume messages from EventBridge:

1. Create the function that will be invoked by EventBridge in serverless.yml:

2. Create the handler script (for example bin/consumer.php):

If you are using Symfony 5.1 or later, use this instead:

3. Register and configure the EventBridgeConsumer service:

Now, anytime a message is dispatched to EventBridge for that source, the Lambda function will be called. The Bref consumer class will put back the message into Symfony Messenger to be processed.

Error handling

AWS Lambda has error handling mechanisms (retrying and handling failed messages). Because of that, this package does not integrates Symfony Messenger's retry mechanism. Instead, it works with Lambda's retry mechanism.

This section is work in progress, feel free to contribute to improve it.

When a message fails with SQS, by default it will go back to the SQS queue. It will be retried until the message expires. Here is an example to setup retries and "dead letter queue" with SQS:

When using SNS and EventBridge, messages will be retried by default 2 times.

Configuration

Configuring AWS clients

By default, AWS clients (SQS, SNS, EventBridge) are preconfigured to work on AWS Lambda (thanks to environment variables populated by AWS Lambda).

However, it is possible customize the AWS clients, for example to use them outside of AWS Lambda (locally, on EC2…) or to mock them in tests. These clients are registered as Symfony services under the keys:

• bref.messenger.sqs_client
• bref.messenger.sns_client
• bref.messenger.eventbridge_client

For example to customize the SQS client:

Disabling transports

By default, this package registers Symfony Messenger transports for SQS, SNS and EventBridge.

If you want to disable some transports (for example in case of conflict), you can remove BrefMessengerBundle from config/bundles.php and reconfigure the transports you want in your application's config. Take a look at Resources/config/services.yaml to copy the part that you want.

Customizing the serializer

If you want to change how messages are serialized, for example to use Happyr message serializer, you need to add the serializer on both the transport and the consumer. For example: