AWS Cost Management Made Easy: Build Your Own Calculator with the AWS Pricing API

#aws #finops #level200 #optimization

When discussing AWS pricing with customers, limitations in the official AWS Pricing Calculator can sometimes hinder accurate cost estimations. This blog post addresses a specific challenge encountered with Amazon CloudWatch Synthetics pricing and provides a solution by building a custom calculator using the AWS Pricing API.

Amazon CloudWatch Synthetics is a service that allows you to create canaries—configurable scripts that run on a schedule to monitor your endpoints and APIs. One of the main challenges we faced was the need to compare different setups of CloudWatch Synthetics, such as defining the number of runs per hour and generating comparison tables—features not available in the AWS Calculator.

By following this guide, you'll learn how to create tailored calculators for any AWS service. Our solution allows flexible configurations and side-by-side comparisons, enabling better decisions when choosing the most cost-effective monitoring setup.

Note: The hosted example has been removed. Use this guide to create your own calculator or adapt it for other use cases.

Prerequisites

Make sure you have:

An AWS account with permissions to:
- Create/manage AWS Lambda functions
- Access the AWS Pricing API
- Work with Amazon S3 and Amazon CloudFront
- Manage Amazon Route 53 (for custom domains)
Basic knowledge of:
- Python, AWS Lambda, Amazon S3
- HTML, CSS, and JavaScript
AWS CLI installed
A code editor

Architecture Overview

Amazon S3: Hosts the static site and pricing JSON.
Amazon CloudFront: Distributes content globally.
Amazon Route 53: Manages your domain.
AWS Lambda: Retrieves pricing from AWS Pricing API.
Amazon EventBridge: Triggers AWS Lambda function daily.

Workflow

AWS Lambda function fetches pricing from AWS Pricing API (available only in us-east-1)
JSON is stored in Amazon S3 and served via CloudFront

Example format:

{
  "us-east-1": {"USD": "0.0012000000"},
  "eu-central-1": {"USD": "0.0016000000"}
}

Implementation Guide

AWS Lambda Function Setup

Requirements:

IAM permissions: Pricing API, S3 write, CloudWatch logs
Set env var: s3_bucket

Lambda function source: GitHub – Lambda function code

Key Function Steps

Initialize

import json, boto3, os

Extract prices

def extract_prices(data):
    prices = {}
    for item in data:
        region = item['product']['attributes']['regionCode']
        terms = item['terms']['OnDemand']
        for val in terms.values():
            for dim in val['priceDimensions'].values():
                prices[region] = dim['pricePerUnit']
    return prices

Main handler

def lambda_handler(event, context):
    pricing = boto3.client('pricing', region_name='us-east-1')
    response = pricing.get_products(
        ServiceCode='AmazonCloudWatch',
        Filters=[{"Type": "TERM_MATCH", "Field": "productFamily", "Value": "Canaries"}],
        FormatVersion='aws_v1',
        MaxResults=100
    )
    prices = extract_prices([json.loads(i) for i in response['PriceList']])
    boto3.client('s3').put_object(
        Bucket=os.getenv('s3_bucket'),
        Key='canarycalc/prices.json',
        Body=json.dumps(prices)
    )

Front-End Integration

Use the generated JSON to build a static front-end app using HTML/CSS/JS. Example code: GitHub – Frontend

Troubleshooting

S3 error: Check permissions
Pricing API failure: Validate filters and region

Resources

Final Thoughts

This basic example can be extended to any AWS service. Explore the full pricing API responses and tailor logic for your FinOps needs, including support for Savings Plans or free tier.

You can even implement pricing logic in spreadsheets or custom dashboards for business use.

AWS pricing is complex—but with automation, it's manageable.

— Alexey--