How to implement a Dead Letter Queue using AWS

Question

I'm trying to implement a dead letter queue for failed lambda events. I created an SQS queue and two lambdas. One lambda only throws an error and the other listens to the SQS queue and is triggered when the queue receives a message and logs the event to Cloudwatch.

In the AWS management console, I am able to see that the .function lambda (the one that throws an error) has a dead letter queue configured.

I am able to see that the .dispatcher function (the one that listens to SQS) is configured correctly and if I send a message to the SQS queue I can also see Cloudwatch logs showing it's being triggered as expected.

Although everything seems to be configured correctly, I am unable to get the .function to send an event to SQS when it's failed in order to trigger the .dispatcher lambda.

I've watched multiple videos, read documentation and I have not been able to figure out why this is not working. I've also tried the onError configuration but, no luck there either.

handler.js

module.exports.function = async (event) => {
    throw new Error('Throwing error 🚨')
}

module.exports.dispatcher = async (event) => {
  try {
    console.log(`Dispached Event:${JSON.stringify(event)}`)
  } catch (error) {
    console.log(error)
    return error
  }
}

serverless.yml

service: dlq-example

frameworkVersion: '3'

provider:
  name: aws
  runtime: nodejs14.x
  iam:
    role:
      statements:
        # Allow functions to list all buckets
        - Effect: Allow
          Action: '*'
          Resource: '*'

plugins:
  - serverless-plugin-lambda-dead-letter

functions:
  hello:
    handler: handler.function
    description: Throws error.
    deadLetter:
      targetArn:
        GetResourceArn: DeadLetterQueue

  dispatcher:
    handler: handler.dispatcher
    description: Dispatcher function. Configured to be triggered by events sent to SQS and handle them.
    events:
      - sqs:
          arn:
            Fn::GetAtt:
              - DeadLetterQueue
              - Arn
resources:
  Resources:
    DeadLetterQueue:
      Type: AWS::SQS::Queue
      Properties:
        QueueName: dlq

Here are images of what I see in the AWS management console:

Screenshot of handler.function lambda (the one that has the DLQ configured)

Screenshot of the handler.dispatcher function (The one that listens to SQS and handles each message)

Screenshot of the SQS queue and the lambda trigger configuration.

Answer 1

For anyone who stumbles across this issue in the future. My configuration was correct, I was missing a SQS queue policy. Once I configured a policy everything worked as expected.