Serverless AWS Lambda Development · Lesson

S3 for File Storage and Events

Deepen your understanding of using Amazon S3 for storing and retrieving large objects, and how S3 events can trigger Lambda for processing.

S3 for File Storage and Events is a free Serverless AWS Lambda Development lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Serverless AWS Lambda Development learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

S3 & Lambda: Event Power

Welcome! In this lesson, we'll dive into how Amazon S3, a powerful storage service, works hand-in-hand with AWS Lambda.

You'll learn to store and retrieve files, and critically, how S3 can trigger your Lambda functions automatically when something happens to your data.

Amazon S3: Cloud Storage

Amazon S3 (Simple Storage Service) is a highly scalable, durable, and available object storage service.

It stores data as objects within buckets.
Objects are files (images, videos, documents) and their metadata.
Buckets are like top-level folders, globally unique names.
S3 is perfect for storing large amounts of unstructured data.

Storing Objects in S3

You can easily put objects into an S3 bucket. Each object has a key, which is its unique identifier within the bucket.

Console: Upload files directly via the AWS Management Console.
CLI: Use the AWS Command Line Interface for scripted uploads.
SDKs: Programmatically upload from your application using AWS SDKs (e.g., Python Boto3, Node.js SDK).

Retrieving Objects from S3

Getting your data back from S3 is just as simple. You reference the bucket name and the object's key.

S3 also offers features like versioning to keep multiple versions of an object, and pre-signed URLs for temporary, secure access to private objects.

S3 Event Notifications

One of S3's most powerful features for serverless is Event Notifications. S3 can notify you when specific events occur in your buckets.

These events include:

Object creation (PUT, POST, COPY)
Object deletion
Object restoration from Glacier

These notifications can be sent to various AWS services, including Lambda functions!

Configure an S3 Trigger

Setting up an S3 trigger for Lambda is done via the S3 console or infrastructure-as-code tools.

You specify:

The event type (e.g., ObjectCreated:Put).
The destination (your Lambda function).
Optional prefix or suffix to filter events (e.g., only trigger for files in the images/ folder or .jpg files).

Lambda Processing S3 Events

When an S3 event occurs, Lambda invokes your function and passes the event details as a JSON payload to your handler. Let's see an example in Python.

import json

def lambda_handler(event, context):
    print("Received S3 event!")
    for record in event['Records']:
        bucket_name = record['s3']['bucket']['name']
        object_key = record['s3']['object']['key']
        event_name = record['eventName']

        print(f"Bucket: {bucket_name}")
        print(f"Object Key: {object_key}")
        print(f"Event Type: {event_name}")

        # In a real scenario, you'd download and process the object here
        # using the bucket_name and object_key
        print(f"Processing '{object_key}' from '{bucket_name}'...")

    return {
        'statusCode': 200,
        'body': json.dumps('S3 event processed successfully!')
    }

Understanding Event Payload

The event object passed to your Lambda function's handler contains crucial information about the S3 event.

Records: A list, as multiple events can be batched.
s3: Contains details about the bucket and object involved.
bucket.name: The name of the S3 bucket.
object.key: The full path/key of the object that triggered the event.
eventName: Describes the specific S3 action (e.g., ObjectCreated:Put).

Common Use Case: Image Resize

A classic serverless pattern is image processing. Imagine a mobile app where users upload photos:

User uploads a high-res image to an S3 bucket.
S3 triggers a Lambda function (e.g., ObjectCreated:Put event).
Lambda downloads the image, resizes it to various thumbnails.
Lambda uploads the thumbnails to a different S3 bucket.

This is highly scalable and cost-effective!

S3 Event Triggers Check

Which of the following statements are TRUE about S3 Event Notifications for Lambda?

Recap: S3 Events for Lambda

Great job! You've learned how S3 acts as both a storage solution and a powerful event source for Lambda.

S3 stores objects in buckets, offering high durability and scalability.
S3 Event Notifications allow specific actions (like object creation/deletion) to trigger Lambda functions.
Lambda functions receive a JSON payload with event metadata, not the full object.
This pattern enables powerful serverless workflows like image processing or data transformations.

Frequently asked questions

Is the “S3 for File Storage and Events” lesson free?

Yes — the full text of “S3 for File Storage and Events” is free to read here on the web, and the Serverless AWS Lambda Development course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Serverless AWS Lambda Development course, upgrade to CoddyKit PRO.

What will I learn in “S3 for File Storage and Events”?

Deepen your understanding of using Amazon S3 for storing and retrieving large objects, and how S3 events can trigger Lambda for processing. You practise Serverless AWS Lambda Development with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Serverless AWS Lambda Development?

No prior experience is required. Serverless AWS Lambda Development on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “S3 for File Storage and Events” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Serverless AWS Lambda Development lesson?

Yes. Every Serverless AWS Lambda Development lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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