Example of a state machine in AWS using step functions

check_age_range_lambda.py

import datetime
import json


def lambda_handler(event, context):
    registration_info = event['registration_info']
    print(registration_info)

    dob = registration_info['child']['dateOfBirth']
    today = datetime.date.today()
    dob_date = datetime.datetime.strptime(dob, '%Y-%m-%d').date()
    age = today.year - dob_date.year - ((today.month, today.day) < (dob_date.month, dob_date.day))

    if age < 2 or age > 5:
        return {
            'statusCode': 400,
            'body': 'Child is not within age range for this daycare'
        }
    
    # Modifies the input data
    registration_info['child']['age'] = age

    return {
        'statusCode': 200,
        'body': json.dumps({'registration_info': registration_info})
    }

check_information_lambda.py

import json
import datetime


def lambda_handler(event, context):
    registration_info = event['registration_info']

    required_fields = ['child', 'parents', 'daysOfWeek']
    for field in required_fields:
        if field not in registration_info:
            return {
                'statusCode': 400,
                'body': f"Missing required field: {field}"
            }
    
    return {
        "statusCode": 200,
        "body": json.dumps(registration_info)
    }

check_spot_availability_lambda.py

import json


def lambda_handler(event, context):
    print(event)
    registration_info = event['registration_info']

    # Placeholder for actual availability check logic
    spots_available = 20  # This should be dynamically determined, not hardcoded

    if spots_available <= 0:
        return {
            'statusCode': 400,
            'body': json.dumps('No spots available in the daycare.')
        }

    # If spots are available, return the registration_info without changes
    return {
        'statusCode': 200,
        'body': json.dumps(registration_info)
    }

sample_input.json

{
  "registration_info": {
    "child": {
      "firstName": "Mohamed",
      "lastName": "Diallo",
      "dateOfBirth": "2022-07-01"
    },
    "parents": {
      "mother": {
        "firstName": "Aicha",
        "lastName": "Cisse",
        "email": "aicha.cisse@example.com",
        "phone": "123-456-7890"
      },
      "father": {
        "firstName": "Ibrahim",
        "lastName": "Diallo",
        "email": "ibrahim.diallo@example.com",
        "phone": "098-765-4321"
      }
    },
    "daysOfWeek": [
      "Monday",
      "Tuesday",
      "Wednesday",
      "Thursday",
      "Friday"
    ],
    "specialInstructions": "Mohamed has a peanut allergy."
  }
}

state_language_code.json

{
  "Comment": "A simple AWS Step Functions state machine that automates a daycare registration workflow.",
  "StartAt": "Check Information",
  "States": {
    "Check Information": {
      "Type": "Task",
      "Resource": "arn:aws:states:::lambda:invoke",
      "Output": "{% $states.result.Payload %}",
      "Arguments": {
        "FunctionName": "arn:aws:lambda:eu-west-2:XXXXX:function:CheckInformation:$LATEST",
        "Payload": "{% $states.input %}"
      },
      "Assign": {
        "statusCode": "{% $states.result.Payload.statusCode %}"
      },
      "Retry": [
        {
          "ErrorEquals": [
            "Lambda.ServiceException",
            "Lambda.AWSLambdaException",
            "Lambda.SdkClientException",
            "Lambda.TooManyRequestsException"
          ],
          "IntervalSeconds": 1,
          "MaxAttempts": 3,
          "BackoffRate": 2,
          "JitterStrategy": "FULL"
        }
      ],
      "Next": "Information Check Result"
    },
    "Information Check Result": {
      "Type": "Choice",
      "Choices": [
        {
          "Condition": "{% $statusCode = 200 %}",
          "Next": "Check age range"
        },
        {
          "Condition": "{% $statusCode = 400 %}",
          "Next": "Notify Missing Info"
        }
      ]
    },
    "Notify Missing Info": {
      "Type": "Fail",
      "Error": "InformationIncomplete",
      "Cause": "The parent did not provide complete information."
    },
    "Check age range": {
      "Type": "Task",
      "Resource": "arn:aws:states:::lambda:invoke",
      "Output": "{% $states.result.Payload %}",
      "Arguments": {
        "FunctionName": "arn:aws:lambda:eu-west-2:XXXXXXX:function:CheckAgeRange:$LATEST",
        "Payload": "{% $states.context.Execution.Input %}"
      },
      "Assign": {
        "ageStatusCode": "{% $states.result.Payload.statusCode %}",
        "modifiedBody": "{% $states.result.Payload.body %}"
      },
      "Retry": [
        {
          "ErrorEquals": [
            "Lambda.ServiceException",
            "Lambda.AWSLambdaException",
            "Lambda.SdkClientException",
            "Lambda.TooManyRequestsException"
          ],
          "IntervalSeconds": 1,
          "MaxAttempts": 3,
          "BackoffRate": 2,
          "JitterStrategy": "FULL"
        }
      ],
      "Next": "Age Check Result"
    },
    "Age Check Result": {
        "Type": "Choice",
        "Choices": [
          {
            "Condition": "{% $ageStatusCode = 200 %}",
            "Next": "Check Spots Availability"
          },
          {
           "Condition": "{% $ageStatusCode = 400 %}",
            "Next": "Notify Invalid Age"
          }
        ]
    },
    "Notify Invalid Age": {
        "Type": "Fail",
        "Error": "InvalidAge",
        "Cause": "The child does not meet the age requirements."
    },
    "Check Spots Availability": {
        "Type": "Task",
        "Resource": "arn:aws:states:::lambda:invoke",
        "Output": "{% $states.result.Payload %}",
        "Arguments": {
            "FunctionName": "arn:aws:lambda:eu-west-2:xxxxxx:function:CheckSpotAvailable:$LATEST",
            "Payload": "{% $modifiedBody %}"
        },
        "Assign": {
            "checkStatusCode": "{% $states.result.Payload.statusCode %}"
        },
        "Next": "Spot Availability Result"
    },
    "Spot Availability Result": {
        "Type": "Choice",
        "Choices": [
          {
            "Condition": "{% $checkStatusCode = 200 %}",
            "Next": "Confirm Registration"
          },
          {
            "Condition": "{% $checkStatusCode = 400 %}",
            "Next": "Notify No Spots"
          }
        ]
    },
    "Notify No Spots": {
        "Type": "Fail",
        "Error": "NoSpots",
        "Cause": "There are no spots available."
    },
     "Confirm Registration": {
      "Type": "Succeed",
      "Comment": "Registration succeeded!"
    }
  },
  "QueryLanguage": "JSONata"
}