How can I programmatically pass the current iteration index as input to an ECS task?

Question

I have the following definition. I want to be able to pass the current iteration number of the map to my ecs task like this python src.py --my_argument <index>. I used "$$.Map.Item.Index" but it doesn't work. I just runs it literally like this: python src.py --my_argument $$.Map.Item.Index

{
  "Comment": "A state machine that iterates over an array and creates an ECS task for each item.",
  "StartAt": "IterateArray",
  "States": {
    "IterateArray": {
      "Type": "Map",
      "InputPath": "$.arrayField", 
      "ItemsPath": "$", 
      "MaxConcurrency": 0,
      "Iterator": {
        "StartAt": "RunECSTask",
        "States": {
          "RunECSTask": {
            "Type": "Task",
            "Resource": "arn:aws:states:::ecs:runTask.sync",
            "Parameters": {
              "LaunchType": "FARGATE",
              "Cluster": "ClusterName",
              "TaskDefinition": "TaskDefinitionName",
              "Overrides": {
                "ContainerOverrides": [
                  {
                    "Name": "yourContainerName",
                    "Command": [
                      "python",
                      "src.py",
                      "--my_argument",
                      "$$.Map.Item.Index"
                    ]
                  }
                ]
              }

            },
            "End": true
          }
        }
      },
      "End": true
    }
  }
}

fedonev · Accepted Answer · 2024-02-12 15:30:02Z

0

Replace "Command" with "Command.$". Appending .$ to a key tells Step Functions to interpolate the path references in the value.

See Passing Data to an Amazon ECS Task in the docs for more examples.

answered Feb 12, 2024 at 15:30

fedonev

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2 Comments

james pow Over a year ago

that didn't work for me because I think it was trying to pass the entire content instead of the value of the current iteration so I had to try something else. Can you pls take a look at my follow up question though?: stackoverflow.com/questions/77992087/…

fedonev Over a year ago

@jamespow OP: "I want to be able to pass the current iteration number".

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