Serverless EMI Calculator using AWS Lambda and API Gateway

Overview

This repository contains a serverless EMI calculator built with AWS Lambda and API Gateway. The application is designed to calculate the Equated Monthly Installment (EMI) based on principal, interest rate, and time period. It uses Python for the Lambda function and integrates with API Gateway to expose the functionality via HTTP requests.

Documentation

• Installation and Usage

Prerequisites

• AWS Account
• Basic understanding of AWS Lambda and API Gateway
• Python 3.9 runtime environment

Steps to Deploy

Step 1: Create AWS Lambda Function

1. Login to the AWS Management Console.
2. Search for Lambda in the service bar.
3. Create a new Lambda function:
   • Function Name: lambda-emi-calc
   • Runtime: Python 3.9
   • Click Create Function.

Step 2: Add Python Code

1. Clear existing code in the Lambda function editor.

2. Paste the following Python code:

   import json
   print('Loading function... Lambda EMI calculator using API Gateway')
   
   def lambda_handler(event, context):
       # 1. Parse out query string params
       principal = int(event['queryStringParameters']['p'])
       rate = float(event['queryStringParameters']['r'])
       time = int(event['queryStringParameters']['t'])
       emi = emi_calculator(principal, rate, time)
       # 2. Construct the body of the response object
       transactionResponse = {
           'p': principal,
           'r': rate,
           't': time,
           'emi': emi
       }
   
       # 3. Construct http response object
       responseObject = {
           'statusCode': 200,
           'headers': {
               'Content-Type': 'application/json'
           },
           'body': json.dumps(transactionResponse)
       }
       # 4. Return the response object
       return responseObject
   
   def emi_calculator(p, r, t):
       r = r / (12 * 100)  # one month interest
       t = t * 12  # one month period
       emi = (p * r * pow(1 + r, t)) / (pow(1 + r, t) - 1)
       return emi

3. Deploy the Lambda function.

Step 3: Test the Lambda Function

1. Configure a test event with the following input:

   {  
     "queryStringParameters": {  
       "p": 10000,  
       "r": 2.5,  
       "t": 5  
     } 
   }

2. Run the test to ensure there are no errors and the output is correct.

Step 4: Set Up API Gateway

1. Search for API Gateway in the service bar.

2. Create a new API Gateway:

   • API Name: EmiCalcApi
   • Description: EmiCalcApi
   • Endpoint Type: Regional
   • Click Create API.

3. Create a Resource:

   • Resource Name: emi
   • Click Create Resource.

4. Create a Method:

   • Method Type: GET
   • Integration Type: Lambda Function
   • Lambda Proxy Integration: Enabled
   • Select the Lambda function lambda-emi-calc.
   • Click Create Method.

Step 5: Deploy the API

1. Click Deploy API.

2. Stage Name: dev

   • Deployment Description: dev
   • Click Deploy.

3. Go to the Stage section and click Edit.

4. Update parameters as needed:

   • Rate (r): Set to 5.8
   • Time (t): Set to 10

5. Copy the Invoke URL from the stage details and append the following query string:

   /emi?p=10000&r=5.8&t=10
   

6. Paste the complete URL into your browser to get the EMI result.

Output

The Lambda function will return a JSON response with the EMI calculation, including the principal, rate, time, and calculated EMI.

License

This project is licensed under the MIT License - see the LICENSE file for details.