Amazon web services – AWS Step Functions: How to set a condition in choice state, if date is less that current date minus 24 hours?

In AWS Step Functions, the "Choice" state enables you to perform conditional branching in your state machine based on the values of the input. However, the "Choice" state doesn’t have the ability to perform arithmetic operations or compute time differences out-of-the-box. To make date comparisons like the one you described, you’d typically need to involve a Lambda function.

Here’s how you can achieve this:

1. Lambda Function for Date Comparison:
   Create a Lambda function that:

   • Accepts the input date in ISO 8601 format.
   • Computes the difference between the current date and the provided date.
   • Returns a result indicating whether the input date is more than 24 hours old.

2. Choice State in Step Functions:
   After invoking the Lambda function, use a Choice state to branch based on the result of the Lambda function.

Here’s a high-level example:

Lambda Function (Python):

import datetime

def lambda_handler(event, context):
    input_date_str = event.get('date')
    input_date = datetime.datetime.fromisoformat(input_date_str)
    
    current_date = datetime.datetime.utcnow()
    delta = current_date - input_date

    return {
        'isMoreThan24Hours': delta.total_seconds() > 86400  # 24 hours = 86400 seconds
    }

State Machine:

{
  "Comment": "A state machine that checks if a date is more than 24 hours old.",
  "StartAt": "CheckDate",
  "States": {
    "CheckDate": {
      "Type": "Task",
      "Resource": "arn:aws:lambda:REGION:ACCOUNT_ID:function:YourLambdaFunctionName",
      "Next": "IsOlderThan24Hours"
    },
    "IsOlderThan24Hours": {
      "Type": "Choice",
      "Choices": [
        {
          "Variable": "$.isMoreThan24Hours",
          "BooleanEquals": true,
          "Next": "MoreThan24HoursBranch"
        }
      ],
      "Default": "LessThan24HoursBranch"
    },
    "MoreThan24HoursBranch": {
      "Type": "Pass",
      "Result": "The date is older than 24 hours.",
      "End": true
    },
    "LessThan24HoursBranch": {
      "Type": "Pass",
      "Result": "The date is less than 24 hours old.",
      "End": true
    }
  }
}

In this design, the state machine invokes the Lambda function, and based on the result, it goes to one of the two branches: MoreThan24HoursBranch or LessThan24HoursBranch.