Lambda with S3 event triggers in AWS - Mini Project: Build & Apply

Lambda with S3 event triggers

📖 Scenario: You are setting up an AWS Lambda function that automatically runs when a new file is uploaded to an S3 bucket. This helps process files without manual steps.

🎯 Goal: Build an AWS Lambda function triggered by S3 upload events using Infrastructure as Code. You will create the S3 bucket, configure the Lambda function, and connect the trigger.

📋 What You'll Learn

Create an S3 bucket named exactly my-upload-bucket

Create a Lambda function named exactly ProcessUploadFunction

Configure the Lambda function with runtime python3.12

Set the Lambda function handler to lambda_function.lambda_handler

Add an S3 event trigger on my-upload-bucket for ObjectCreated events

Use valid AWS CloudFormation YAML syntax

💡 Why This Matters

🌍 Real World

Automating file processing workflows by triggering Lambda functions on file uploads to S3 is common in data pipelines, image processing, and serverless applications.

💼 Career

Understanding how to connect AWS Lambda with S3 event triggers is essential for cloud engineers and developers working on serverless architectures and event-driven systems.

1

Create the S3 bucket resource

Create an AWS CloudFormation resource for an S3 bucket named my-upload-bucket. Use the logical ID UploadBucket.

AWS

# Your code here

Need a hint?

Use AWS::S3::Bucket as the resource type and set BucketName property.

2

Add the Lambda function resource

Add a Lambda function resource with logical ID ProcessUploadFunction. Set Runtime to python3.12, Handler to lambda_function.lambda_handler, and use a placeholder Role ARN arn:aws:iam::123456789012:role/lambda-exec-role.

AWS

Resources:
  UploadBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: my-upload-bucket
# Your code here

Need a hint?

Use AWS::Lambda::Function as the resource type and set the required properties.

3

Add S3 event trigger to Lambda

Add an Event source to the Lambda function to trigger on ObjectCreated events from the my-upload-bucket S3 bucket. Use the Events property with logical ID S3UploadEvent inside the Lambda resource.

AWS

Resources:
  UploadBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: my-upload-bucket
  ProcessUploadFunction:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: ProcessUploadFunction
      Runtime: python3.12
      Handler: lambda_function.lambda_handler
      Role: arn:aws:iam::123456789012:role/lambda-exec-role
      Code:
        ZipFile: |
          def lambda_handler(event, context):
              return 'Hello from Lambda'
# Your code here

Need a hint?

Use the Events property inside the Lambda resource to add the S3 trigger.

4

Add permission for S3 to invoke Lambda

Add an AWS::Lambda::Permission resource with logical ID AllowS3Invoke to allow the S3 bucket my-upload-bucket to invoke the Lambda function ProcessUploadFunction. Set Action to lambda:InvokeFunction, Principal to s3.amazonaws.com, and SourceArn to the ARN of my-upload-bucket.

AWS

Resources:
  UploadBucket:
    Type: AWS::S3::Bucket
    Properties:
      BucketName: my-upload-bucket
  ProcessUploadFunction:
    Type: AWS::Lambda::Function
    Properties:
      FunctionName: ProcessUploadFunction
      Runtime: python3.12
      Handler: lambda_function.lambda_handler
      Role: arn:aws:iam::123456789012:role/lambda-exec-role
      Code:
        ZipFile: |
          def lambda_handler(event, context):
              return 'Hello from Lambda'
      Events:
        S3UploadEvent:
          Type: S3
          Properties:
            Bucket: my-upload-bucket
            Events: s3:ObjectCreated:*
# Your code here

Need a hint?

Use AWS::Lambda::Permission to allow S3 to invoke the Lambda function.