AWS SQS doesn't reliably trigger Lambda

Question

I've set up a small serverless app using Lambda and SQS. In my case i wanted to trigger a lambda every time a message is added to a SQS Queue.

functions in my serverless.yml

functions:
  collectGame:
    handler: js/collect.collectGame
    memorySize: 128
    timeout: 10
    events:
    - sqs:
        arn:
          Fn::GetAtt:
            - gameRequestQueue
            - Arn
    - http:
        method: post
        cors:
          origin: "https://my-api-url.com"
        path: get/game/{id}
        private: true
        request:
          parameters:
            paths:
              id:true

I tested the process by sending 31 Messages at once to the Queue but realized that only 9 Lambdas get executed (by looking into the cloudwatch logs). I looked into the Queue and can confirm that its being filled with all the messages and that its empty after the 9 Lambdas have been triggered.

I'd expect to have 31 Lambda executions but thats not the case. Anyone knows potential reasons why my Lambdas are not being triggered by the messages?

Answer 1

Your lambda function is probably being invoked with multiple messages. You should be able to set the BatchSize to 1 when you create the event source mapping, if you only want one message to be sent per lambda invocation

It looks like you are using the serverless framework. See their SQS event documentation for setting the batch size.