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SQS to Lambda (via Lambda)

There is currently not a native SQS event source for Lambda. This is unfortunate. You can run something like https://github.com/robinjmurphy/sqs-to-lambda but that requires running an instance, and who wants to do that?

Running a Lambda function (128MB) full-time costs about $5.39/month, and a t2.nano (on demand) costs $4.68. Surely $0.71 is worth the coolness of not running a boring EC2 instance. (There's a cheaper option too, keep reading.)

The supplied CloudFormation template will set up a Lambda function that reads from SQS queues, and invokes Lambda functions with the payloads. By default it will run a Lambda function continuously, polling your queues constantly for new items.

You can also configure it to poll your queues once a minute, reducing Lambda costs to almost nothing, at the expense of waiting up to 60s to receive new queue items.

One day, hopefully soon, Lambda will likely support SQS as a native event source, and then this will be completely unnecessary. :fingerscrossed:

Getting Started

First, create the CloudFormation stack. Inside a clone of this project:

aws --region us-east-1 cloudformation create-stack                            \
  --stack-name sqs-to-lambda                                                  \
  --template-body file://cloudformation.json                                  \
  --parameters 'ParameterKey=QueueToFunctionMapping,ParameterValue="<queue url 1>,<function 1>,<queue url 2>,<function 2>,..."' \
  --capabilities CAPABILITY_IAM

If you'd like the every-minute, cheaper option, add ParameterKey=Frequency,ParameterValue=1Minute to the --parameters option.

You can also use the console, if you are so inclined.

Your functions specified in QueueToFunctionMapping will now receive everything sent to their respective queues. The payload is an object with source set to aws.sqs and Message as the actual message from SQS:

{
    "source": "aws.sqs",
    "QueueUrl": "https://sqs.us-east-1.amazonaws.com/1234567/my-queue",
    "Message": {
        "MessageId": "2b2ea032-5d3d-4a17-b38c-92bece3ad7ce",
        "ReceiptHandle": "AQEB8t7sz7fgeAalKraYO3brB2+r0d3p18RE3G6J9k9GmRFODibL64oget5R6NaRJDoYrwHNtLutKOiY3Ggls2F6LRJFKLZhLbr3fSd+Hg6KiECu4tfdyAZxAwj2/X5QIieu0dtCMIEujHSDn7Xzz9L5hNW/uCB7Tx7Km0Sal077KE4h4CCHMvZDza8bNzmFTXvfRj5+odG80oLtir0w+lwx+DQYnkIZJxvVRLkfOspU2/84/ye4VZkr8pOD7xIGtgzU/Z7pdzTXeKw0WSfHQoQ661qBcqBHhMTjXXZ0WzsYHW1HPqtSwqA760nZfh0RXRjo9AGFsXYmtnQoFs64PCJ1hZ2u+N+azHChx4Ma+PtT6pgUfkCzrYG5Gq/BaR+RmPsW",
        "MD5OfBody": "abecffaa52f529a2b83b6612a7964b02",
        "Body": "{\"foo\":\"bar\"}"
    }
}

NOTE: Your Lambda function will need to delete the item from the queue using the given ReceiptHandle! Otherwise, it will keep getting delivered.

Questions

How does it work?

The supplied CloudFormation template will create a Lambda function that knows how to pull from queues, and invoke other Lambda functions. The function is triggered by CloudWatch Events, also set up by the CloudFormation template. CloudWatch Events are not yet supported directly by CloudFormation, so another Lambda function is supplied to create them as a custom resource.

If you choose Continuous frequency, the function is invoked every 5 minutes, and runs for almost 5 minutes, constantly polling.

If you choose 1Minute frequency, the function is invoked every minute, but exits once the queue returns 0 items to process.

What's up with the cloudformation.yml file?

Yaml is a much easier format to write these in. Trust me.

What's up with the Javascript in cloudformation.json?

Embedding Javascript in the CloudFormation template is an easy way to make the template self-contained. It also allows us to dynamically inject the configuration into the SQS poller function. The javascript in the cloudformation.json file is minimized from sqs-to-lambda.js and cloudwatch-rule-custom-event.js.

We minimize the Javascript because there is a 2KB limit to inline code in CloudFormation templates.

Building

The cloudformation.json file is a build artifact - don't edit it directly! To build:

$ npm install
$ npm run build

Contributing

Make your changes, build a new cloudformation.json file (see above), and submit a pull request.