💸 How I Automated AWS Billing Control with Lambda, SNS & Boto3

#cloudcomputing #awschallenge #aws #webdev

Introduction

Have you ever worried about unexpected AWS billing due to resources running in the background? ☁️💸

In this blog, I’ll walk you through how I automated my AWS cost control by:

Setting up a Lambda function with Boto3
Using AWS SNS to trigger alerts
Creating a Billing Budget
Automatically stopping EC2 instances when billing crosses $0.01.

Step 1:Create SNS Topic to triger Lambda

Go to SNS > Topics
Click Create topic
Type: Standard
Name: BudgetAlertsTopic
Create topic
In "Subscriptions" tab → click Create subscription
Protocol: Email
Endpoint: Your email
Go to your email inbox → Confirm the subscription

Step 2:Create a Budget

Go to Billing > Budgets **> **Create Budget

Type: Cost Budget
Name: MyBillingBudget
Budget amount: $0.01
Scope: All services
Notifications:
Threshold: 100%
Send to: SNS topic BudgetAlertsTopic
Create budget

Step 3:Create Lambda Function to Stop EC2 + Block S3

Go to IAM > Roles > Create Role
Use Case: Lambda
Permissions → Create new custom policy with:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "ec2:DescribeInstances",
        "ec2:StopInstances",
        "s3:ListBucket",
        "s3:PutPublicAccessBlock"
      ],
      "Resource": "*"
    }
  ]
}

Name the role: LambdaBillingStopperRole

Step 4:Create Lambda Function

Go to Lambda > Create Function
Name: StopAWSResources
Runtime: Python 3.12
Role: Attach LambdaBillingStopperRole

import boto3

def lambda_handler(event, context):
    ec2 = boto3.client('ec2')
    s3 = boto3.client('s3')

    # Stop all EC2 instances
    instances = ec2.describe_instances(Filters=[{'Name': 'instance-state-name', 'Values': ['running']}])
    for reservation in instances['Reservations']:
        for instance in reservation['Instances']:
            ec2.stop_instances(InstanceIds=[instance['InstanceId']])
            print(f"Stopped instance: {instance['InstanceId']}")

    # Block all S3 buckets
    buckets = s3.list_buckets()
    for bucket in buckets['Buckets']:
        s3.put_public_access_block(
            Bucket=bucket['Name'],
            PublicAccessBlockConfiguration={
                'BlockPublicAcls': True,
                'IgnorePublicAcls': True,
                'BlockPublicPolicy': True,
                'RestrictPublicBuckets': True
            }
        )
        print(f"Blocked bucket: {bucket['Name']}")

    return {
        'statusCode': 200,
        'body': 'EC2 stopped and S3 buckets locked.'
    }

Paste this code in the function:

Deploy manually and save the code.

Step:5 Connect SNS to Lambda

Go to SNS > Topics > BudgetAlertsTopic
Click Create subscription
Protocol: AWS Lambda
Endpoint: Select your function StopAWSResources
Go to Lambda → Permissions → Add trigger → Choose SNS and select topic