Step Functions + Map State = Scalable Parallel Fan-Out

Why: Process arrays of tasks in parallel using serverless design. Perfect for batch processing (S3/SQS/DynamoDB), mass API calls, or report generation.

Best Practices:

• Use Map in distributed mode (not inline) if you have more than ~40 iterations.
• Plug in Lambda, ECS, or even nested Step Functions.
• Set maxConcurrency to avoid overloading dependencies.

Use Case: You receive 1,000 orders → Step Function processes each in parallel, logging success/failure.

Example Map state fragment:

{
  "Type": "Map",
  "InputPath": "$.items",
  "ItemsPath": "$",
  "MaxConcurrency": 10,
  "Iterator": {
    "StartAt": "ProcessItem",
    "States": {
      "ProcessItem": {
        "Type": "Task",
        "Resource": "arn:aws:lambda:region:account:function:processItem",
        "End": true
      }
    }
  },
  "End": true
}

Result: pass items: [1,2,3,4,...] — and Step Functions fan-out and trigger processItem Lambda for each.