AWS Step Function - Adding dynamic value to Pass state type

I too got stuck on this before I figured it out.

Pass states can be used, but @ankitkanojia and @shashi 's answers need a minor modification.

If you want to use input paths, the keys inside parameters need to end in ".$" ("totalCount.$")

So the state specification should be as follows:

"loop":{
      "Type": "Pass",
      "Result":{
        "totalCount.$": "$.newFieldsResponse.body.count",
        "currentCount": 0,
        "step": 1
      },
      "ResultPath": "$.iteration",
      "Next":"iterateLoop"
    },

It works in a combination of two of the solutions here exposed:

1. Add Parameter in Pass step
2. Add *.$ in the name of the var you want to pass:

 {
  "loop": {
    "Type": "Pass",
    "parameters": {
      "totalCount.$": "$.newFieldsResponse.body.count",
      "currentCount": 0,
      "step": 1
    },
    "ResultPath": "$.iteration",
    "Next": "iterateLoop"
  }
 }

This is possible through "Parameters" in pass state

JSON

{
  "loop": {
    "Type": "Pass",
    "Parameters": {
      "totalCount": "$.newFieldsResponse.body.count",
      "currentCount": 0,
      "step": 1
    },
    "ResultPath": "$.iteration",
    "Next": "iterateLoop"
  }
}

Looks like this may not be possible. The workaround I did is to use "Parameters" property. From AWS documentation: "For key-value pairs where the value is selected using a path, the key name must end in *.$. ".

So resolved the above by :

1. Changing Pass state to remove any dynamic value reference

"loop":{
      "Type": "Pass",
      "Result":{
        "currentCount": 0,
        "step": 1
      },
      "ResultPath": "$.iteration",
      "Next":"iterateLoop"
    },

2. creating a Parameters property where I need the values as below:

 "iterateLoop":{
      "Type":"Task",
      "Resource": "arn:aws:lambda:....r",
      "Parameters":{
        "totalCount.$": "$.newFieldsResponse.body.count",
        "currentCount.$": "$.iteration.currentCount",
        "step.$": "$.iteration.step"
      },
      "ResultPath": "$.iteration",
      "Next":"continueLoop"
    },

totalCount, currentCount and step all read the value from using a path in the state input. The key needs to be appended with a ".$" at the end.