Building an S3 Event-Driven AWS Lambda to Send Email Alerts and Backup Files

Introduction

In this blog, I’ll walk through a hands-on AWS serverless implementation where an S3 file upload automatically triggers a Lambda function, sends an email notification via SNS, and copies the uploaded object into a backup bucket.

This use case is common in real-world systems where teams need:

• Immediate visibility when files are uploaded

• Automated backups

• Event-driven processing without managing servers

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Problem Statement

Create an S3 event trigger to invoke a Lambda function that:

• Sends an SNS email notification on every file upload

• Copies the uploaded file into a backup S3 bucket

Email notification should include:

• Source Bucket Name

• AWS Region

• File Name and File Size

• Upload IP Address

• Event Time

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AWS Services Used

• Amazon S3 – Object storage and event source

• AWS Lambda – Serverless event processing

• Amazon SNS – Email notification service

• Amazon CloudWatch – Logs and monitoring

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Key Concepts Practiced

Before implementing the solution, I practiced and understood the following Lambda fundamentals:

• Handler – The entry point of the Lambda function

• Event – JSON payload sent by S3 containing upload details

• Context – Runtime metadata such as request ID and execution info

• Test Event – Used for local validation (not used in final execution)

• Environment Variables – Secure way to store configuration values

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Architecture Overview

S3 (PUT Object Event)
→ Lambda Function
→ SNS Email Notification
→ Copy Object to Backup S3 Bucket

This architecture is fully event-driven and serverless.

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Step 1: Configure S3 Event Trigger

An S3 bucket is configured to trigger a Lambda function only when a PUT (ObjectCreated) event occurs.

Concept used:

• S3 Event Notifications allow S3 to notify other AWS services when specific actions occur.

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Step 2: Create an SNS Topic and Subscribers

An SNS topic is created to send email notifications.
Email subscribers are added and confirmed.

Concept used:

• SNS Topics act as a publisher-subscriber messaging system.

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Step 3: Write the Lambda Function Code

The Lambda function performs the following tasks:

• Reads file metadata from the S3 event

• Formats a detailed email message

• Publishes the message to SNS

• Copies the uploaded object to a backup bucket

Lambda Code

import os,json,boto3

s3 = boto3.client("s3")
sns = boto3.client("sns")

def lambda_handler(event,context):
    print(event)
    source_bucket = event['Records'][0]['s3']['bucket']['name']
    aws_region = event['Records'][0]['awsRegion']
    key_val = event['Records'][0]['s3']['object']['key']
    size_val = event['Records'][0]['s3']['object']['size']/1024
    ipAddress = event['Records'][0]['requestParameters']['sourceIPAddress']
    event_time = event['Records'][0]['eventTime']
    message = "Hi, \n The Event time is : " + event_time + "Hi, \nYou are
receiving this email because you are subscribed to this S3event. \nThe Source
Bucket is : " + source_bucket + "\nThe AWS Region is :" + aws_region + "\nThe
Uploaded Filename is : " + key_val + " having Size : " + str(size_val) + " KB" +
"\nThe Object is upload from IP Address: " + ipAddress

 #Below are the variables for copy_object function parameters
 #Provide below the target bucket name where your object needs to be copied
    backupBucket = os.environ['BACKUP_BUCKET_NAME']
    snsArn = os.environ['SNS_TOPIC_ARN']
    emailSubject = "S3EventTrigger-Notification"
    copy_source = {'Bucket' : source_bucket, 'Key' : key_val}
    sns_response = sns.publish(TopicArn=snsArn,Message=message,Subject=emailSubject)
    print(sns_response)
    
    try:
        print("Copying the object from source to destination")
        s3.copy_object(Bucket=backupBucket,Key=key_val, CopySource=copy_source)
 
    except Exception as e:
        print(e)
        print("Error getting object")
        raise e

Concepts used:

• Lambda Handler (lambda_handler)

• Event Object (event['Records'])

• Boto3 SDK for AWS service interaction

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Step 4: Configure Environment Variables

Environment variables are added in Lambda to avoid hard-coding values.

Key	Value
BACKUP_BUCKET_NAME	<Backup_Bucket_Name>
SNS_TOPIC_ARN	<SNS_Topic_ARN>

Concept used:

• Environment Variables provide secure, reusable configuration.

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Step 5: Upload File to Source S3 Bucket

A file is uploaded to the source S3 bucket.

This action automatically triggers the Lambda function.

Concept used:

• Event-driven execution (no manual invocation)

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Step 6: Verify Lambda Execution in CloudWatch

Lambda execution logs are verified in CloudWatch under:

/aws/lambda/<LambdaFunctionName>

Concept used:

• CloudWatch Logs for monitoring and debugging serverless workloads

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Step 7: Verify Backup Bucket

The uploaded file is successfully copied to the backup S3 bucket.

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Step 8: Verify Email Notification

An email notification is received containing:

• Source bucket name

• AWS region

• File name and size

• Upload IP address

• Event time

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Conclusion

This project demonstrates a real-world AWS serverless workflow using S3, Lambda, and SNS.

It highlights how AWS services can be combined to build scalable, automated, and event-driven solutions without managing infrastructure.

Through this exercise, I gained hands-on experience with:

• Lambda internals (handler, event, context)

• S3 event notifications

• SNS messaging

• Environment-based configuration

• CloudWatch monitoring