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. osls 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.

You can set functionResponseType to ReportBatchItemFailures to let your function return a partial success result if one or more messages in the batch have failed.

Check AWS documentation for more details.

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

Setting filter patterns

This configuration allows customers to filter event before lambda invocation. It accepts up to 5 filter patterns by default and up to 10 with quota extension. If one event matches at least 1 pattern, lambda will process it.

For more details and examples of filter patterns, please see the AWS event filtering documentation

Note: osls only sets this property if you explicitly add it to the sqs configuration (see an example below). The following example will only process records where field a is equal to 1 or 2.

functions:
  onlyOneOrTwo:
    handler: handler.preprocess
    events:
      - sqs:
          arn: arn:aws:sqs:region:XXXXXX:myQueue
          filterPatterns:
            - a: [1, 2]

Setting the Maximum Concurrency

The maximum concurrency setting limits the number of concurrent instances of the function that an Amazon SQS event source can invoke. The minimum limit of concurrent functions that the event source can invoke is 2, and the maximum is 1000. To turn off maximum concurrency, leave this field empty.

For more details, see the AWS SQS max concurrency documentation.

functions:
  onlyOneOrTwo:
    handler: handler.preprocess
    events:
      - sqs:
          arn: arn:aws:sqs:region:XXXXXX:myQueue
          maximumConcurrency: 250

Enabling and disabling the event source

The enabled property toggles the Enabled flag of the underlying event source mapping. It defaults to true; set it to false to deploy the mapping in a paused state, so Lambda stops polling the queue and processing messages until you re-enable it.

functions:
  compute:
    handler: handler.compute
    events:
      - sqs:
          arn: arn:aws:sqs:region:XXXXXX:myQueue
          enabled: false

IAM Permissions

osls will automatically configure the minimum 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 plugin that simplifies deploying pieces of applications via "constructs". Lift can be installed via:

osls 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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