AWS Step Function: state A pass lambda output to state B

Question

My AWS lambda function check-version-lambda returns {"latest": "yes"} or {"latest": "no"}.

I have the AWS step function below, to pass above result to next state.

The next state process_version is a choice state, how do I retrieve the input inside Choices? What to fill in for <???>?

  {
      "StartAt": "check_version",
      "States": {
        "check_version": {
          "Type": "Task",
          "Resource": "arn:aws:lambda:us-east-1:000:function:check-version-lambda",
          "OutputPath": "$.latest",
          "Next": "process_version"
        },
        "process_version": {
          "Type": "Choice",
          "Choices": [
            {
              "Variable": "<???>",
              "StringEquals": "yes",
              "Next": "next_state"
            },
            {
              "Variable": "<???>",
              "StringEquals": "no",
              "Next": "next_state"
            }
          ],
          "Default": "next_state"
        }
      }
    }

Answer 1

In your "check_version" state, you can use

"ResultPath": "$.result",
"OutputPath": "$.result",

to explicitly configure the step function to put the result of the lambda (e.g. {"latest": "yes"}) into the result property of the input object. OutputPath tells the step function to only select that result as state output and hand it over to the next state.

In your "process_version" state, you should then be able to use:

"Variable": "$.result.latest",
"StringEquals": "yes",
"Next": ...

Source: https://docs.aws.amazon.com/step-functions/latest/dg/input-output-example.html