SQS Queues

In the following example, we specify that the compute function should be triggered whenever there are messages in the given SQS Queue.

The ARN for the queue can be specified as a string, the reference to the ARN of a resource by logical ID, or the import of an ARN that was exported by a different service or CloudFormation stack.

Note: The sqs event will hook up your existing SQS Queue to a Lambda function. Serverless won't create a new queue for you.

functions:
  compute:
    handler: handler.compute
    events:
      # These are all possible formats
      - sqs: arn:aws:sqs:region:XXXXXX:MyFirstQueue
      - sqs:
          arn:
            Fn::GetAtt:
              - MySecondQueue
              - Arn
      - sqs:
          arn:
            Fn::ImportValue: MyExportedQueueArnId
      - sqs:
          arn:
            Fn::Join:
              - ':'
              - - arn
                - aws
                - sqs
                - Ref: AWS::Region
                - Ref: AWS::AccountId
                - MyOtherQueue

Setting the BatchSize

For the SQS event integration, you can set the batchSize, which effects how many SQS messages can be included in a single Lambda invocation. The default batchSize is 10. The max batchSize is 10000 for a standard queue, 10 for a FIFO queue.

You can also set maximumBatchingWindow to standard queues to specify the maximum amount of time in seconds to gather records before invoking the function. The max maximumBatchingWindow is 300 seconds. Check AWS documentation for more details.

functions:
  compute:
    handler: handler.compute
    events:
      - sqs:
          arn: arn:aws:sqs:region:XXXXXX:myQueue
          batchSize: 10
          maximumBatchingWindow: 60

IAM Permissions

The Serverless Framework will automatically configure the most minimal set of IAM permissions for you. However you can still add additional permissions if you need to. Read the official AWS documentation for more information about IAM Permissions for SQS events.

Deploying SQS queues

The examples above show how to consume messages from an existing SQS queue. To create an SQS queue in serverless.yml, you can either write custom CloudFormation, or you can use Lift.

Lift is a Serverless Framework plugin that simplifies deploying pieces of applications via "constructs". Lift can be installed via:

serverless plugin install -n serverless-lift

We can use the queue construct to deploy an SQS queue with its Lambda consumer:

constructs:
  my-queue:
    type: queue
    worker:
      handler: handler.compute

plugins:
  - serverless-lift

The queue construct deploys:

  • An SQS queue
  • A worker Lambda function: this function processes messages sent to the queue.
  • An SQS "dead letter queue": this queue stores all the messages that failed to be processed.

Read the queue construct documentation to find a complete example with code, and to learn how to configure the batch size, retries and other options.

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