AWS Stepfunction 将数据传递给下一个 lambda 而无需所有额外填充

Question

I have created a state machine with AWD CDK (typescript) and it all works fine. It is just the output of Lambda 1 which is the input for Lambda 2, has some sort of state machine padding which I am not interested in.

Definition of state machine:

{
  "StartAt": "",
  "States": {
    "...applicationPdf": {
      "Next": "...setApplicationProcessed",
      "Type": "Task",
      "Resource": "arn:aws:states:::lambda:invoke",
      "Parameters": {
        "FunctionName": "...applicationPdf",
        "Payload.$": "$"
      }
    },
    "...setApplicationProcessed": {
      "Next": "Done",
      "Type": "Task",
      "Resource": "arn:aws:states:::lambda:invoke",
      "Parameters": {
        "...applicationPdf",
        "Payload.$": "$"
      }
    },
    "Done": {
      "Type": "Succeed"
    }
  }
}

Output of Lambda1 (applicationPdf):

{
  "ExecutedVersion": "$LATEST",
  "Payload": {
    ...
  },
  "SdkHttpMetadata": {
    "AllHttpHeaders": {
      ...
    },
    "HttpHeaders": {
       ....
    },
    "HttpStatusCode": 200
  },
  "SdkResponseMetadata": {
     ....
  },
  "StatusCode": 200
}

So I am only interested in Payload , not all the other stuff. The reason I want to do is that is I want to run the 2nd lambda separately I just want the Event going into the Lambda, to be the Payload object, not the the object with ExecutedVersion etc .

Does anyone know how to do this? I will have a look at the Parameters option of the definition, maybe the answer lies there.

Answer 1

Thanks for your question and for your interest in Step Functions.

The ResultSelector and OutputPath fields can be used to manipulate the output of a state, which can be particularly helpful when a state outputs values which you do not need access to in subsequent states. The difference between them is that ResultSelector is applied before the state's ResultPath is applied, while OutputPath is applied after it.

As you noted, you can use OutputPath to filter out any unwanted metadata before being passed on to the next state.

Answer 2

I found one solution, add the outputPath :

return new LambdaInvoke(this, 'lamba', {
      lambdaFunction: Function.fromFunctionArn(this, name, this.createLabmdaArn('applicationPdf')),
      outputPath: '$.Payload',
    });

This seems to work and might be THE solution.