AWS Lambda – S3 Trigger Integration (Python)

This project demonstrates a basic event-driven architecture using AWS Lambda and Amazon S3. When a file is uploaded to a specific S3 bucket, the Lambda function is triggered and logs the file name to Amazon CloudWatch.

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✅ Objective

• Understand how S3 triggers work with Lambda
• Learn how to handle AWS events in Python
• Practice role-based permissions using IAM
• Monitor function execution via CloudWatch Logs

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🛠️ Services Used

• Amazon S3 – Event source for uploads
• AWS Lambda – Event-driven compute
• IAM – Role for Lambda to access S3 and CloudWatch
• Amazon CloudWatch – To log and view events

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📐 Architecture

1. File uploaded to S3
2. S3 sends an event to Lambda
3. Lambda function logs the filename
4. Output visible in CloudWatch Logs

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🚀 Setup Instructions

1. Create an S3 Bucket

• Go to the S3 console → Create bucket
• Example name: lambda-s3-trigger-demo1
• Ensure ACLs are disabled and public access is blocked

📸 Screenshot:

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2. Create the Lambda Function

• Go to Lambda Console → Create function
• Runtime: Python 3.10
• Permissions: Create a new role with basic Lambda permissions

Paste the following code:

import json

def lambda_handler(event, context):
    file_name = event['Records'][0]['s3']['object']['key']
    print(f"New file uploaded: {file_name}")
    return {
        'statusCode': 200,
        'body': json.dumps(f"Processed file: {file_name}")
    }

📸 Screenshot:

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3. Add S3 as Trigger

• In Lambda → Click Add trigger
• Choose Amazon S3
• Select the bucket created (lambda-s3-trigger-demo1)
• Event type: PUT
• Save

⚠️ If you get a permissions error make sure to check the box: :

“I acknowledge that using the same S3 bucket for both input and output is not recommended...”
Otherwise, the trigger won't be created.

📸 Screenshot:

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4. Upload a File to S3

• Upload a test file (e.g., test.txt) into the S3 bucket

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5. Check Logs in CloudWatch

• Go to CloudWatch → Log Groups → /aws/lambda/your-function-name
• Verify that you see a log like: New file uploaded: test.txt

📸 Screenshot:

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📌 Notes

• This project demonstrates a simple event trigger setup
• You can expand the Lambda to process file content, send notifications, or trigger other AWS services
• Make sure the IAM role has:
  • AmazonS3ReadOnlyAccess
  • AWSLambdaBasicExecutionRole