How to access API Parameters of a node and add them as part of it's own output json in AWS Step Functions?

Question

Here's some part of my StepFunction:
 https://i.stack.imgur.com/4Jxd9.png

Here's the workflow for the "Parallel" node:
```
    {
      "Type": "Parallel",
      "Branches": [
        {
          "StartAt": "InvokeEndpoint01",
          "States": {
            "InvokeEndpoint01": {
              "Type": "Task",
              "End": true,
              "Parameters": {
                "Body": "$.Input",
                "EndpointName": "dummy-endpoint-name1"
              },
              "Resource": "arn:aws:states:::aws-sdk:sagemakerruntime:invokeEndpoint"
            }
          }
        },
        {
          "StartAt": "InvokeEndpoint02",
          "States": {
            "InvokeEndpoint02": {
              "Type": "Task",
              "End": true,
              "Parameters": {
                "Body": "$.Input",
                "EndpointName": "dummy-endpoint-name2"
              },
              "Resource": "arn:aws:states:::aws-sdk:sagemakerruntime:invokeEndpoint"
            }
          }
        }
      ],
      "Next": "Lambda Invoke"
    },
```
I would like to access the `EndpointName` of each node inside this Parallel block and add it as one of the keys of that particular node's output, without modifying the existing output's body and other headers.(in the above json, `EndpointName` can be found for first node inside the Parallel at `$.Branches[0].States.InvokeEndpoint01.Parameters.EndpointName`)

Here's output of one of the node inside the Parallel block:
```
{
  "Body": "{xxxx}",
  "ContentType": "application/json",
  "InvokedProductionVariant": "xxxx"
}
```
and I would like to access the API Parameter and make it something like below:
```
{
  "Body": "{xxxx}",
  "ContentType": "application/json",
  "InvokedProductionVariant": "xxxx",
  "EndpointName": "dummy-endpoint-name1"
}
```

How do I do this?

Answer

Hi,

Two possible solution that I can see are:

1. Define ```ResultSelector``` in each state to insert the static ```EndpointName``` value into the state's result. Adding a value ```"Output.$": "$"``` will copy the full, un-manipulated, state result into that key.

**Example Definition**
```
{
    "StartAt": "InvokeEndpoint02",
    "States":
    {
        "InvokeEndpoint02":
        {
            "Type": "Task",
            "End": true,
            "Parameters":
            {
                "Body": "$.Input",
                "EndpointName": "dummy-endpoint-name2"
            },
            "Resource": "arn:aws:states:::aws-sdk:sagemakerruntime:invokeEndpoint",
            "ResultSelector":
            {
                "Output.$": "$",
                "EndpointName": "dummy-endpoint-name2"
            }
        }
    }
}
```

**Example Output**
```
{
  "EndpointName": "dummy-endpoint-name2",
  "Output": {
    "Body": "{xxxx}",
    "ContentType": "application/json",
    "InvokedProductionVariant": "xxxx"
  }
}
```

2. Pass the ```EndpointName``` into  Amazon SageMaker's ```CustomAttributes``` Request/Response elements, [SageMaker InvokeEndpoint Response Elements](https://docs.aws.amazon.com/sagemaker/latest/APIReference/API_runtime_InvokeEndpoint.html#API_runtime_InvokeEndpoint_ResponseElements). Adding ```EndpointName``` to the model's response in the ```CustomAttributes``` element will result in the desired state result.

Answer

2nd way from @Edward_S's answer does fulfill my needs. but, someone stumbling on this question in the future would want to learn how this can be accomplished.

I learned from AWS Support that it is not possible to access the parameters(or API Parameters) of a node.
If you want to access the Parameters, make a node(at `i-1`th position) send the Parameters current node(at `i`th position) need as Parameters and fill them dynamically and then access them from it's output.

How to access API Parameters of a node and add them as part of it's own output json in AWS Step Functions?

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