AWS: 3 Easy to Write Lambda Functions

Here are three examples of AWS Lambda functions for different use cases. These include the hello world function, image resizing, and fetching data from DynamoDB.

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1. Basic Hello World Function

This is a simple AWS Lambda function that returns a “Hello, World!” message. It’s often used in the AWS Lambda to understand the basics.

def lambda_handler(event, context):
    return {
        'statusCode': 200,
        'body': 'Hello, World!'
    }

2. Image Resizing Function

This function resizes an image uploaded to an S3 bucket. When an image is uploaded, the Lambda function is triggered, resizes it, and stores it in a different S3 bucket.

import boto3
from PIL import Image
import io

s3_client = boto3.client('s3')

def lambda_handler(event, context):
    source_bucket = event['Records'][0]['s3']['bucket']['name']
    source_key = event['Records'][0]['s3']['object']['key']
    target_bucket = 'resized-images-bucket'
    target_key = 'resized-' + source_key
    
    # Download image from S3
    response = s3_client.get_object(Bucket=source_bucket, Key=source_key)
    image_content = response['Body'].read()
    
    # Resize image
    image = Image.open(io.BytesIO(image_content))
    image = image.resize((100, 100))  # Resize to 100x100 pixels
    
    # Convert image to bytes
    buffer = io.BytesIO()
    image.save(buffer, 'JPEG')
    buffer.seek(0)
    
    # Upload the resized image back to S3
    s3_client.put_object(Bucket=target_bucket, Key=target_key, Body=buffer)
    
    return {
        'statusCode': 200,
        'body': f'Resized image saved to {target_bucket}/{target_key}'
    }

Explanation: Event JSON

{
"Records": [
{
"eventVersion": "2.1",
"eventSource": "aws:s3",
"awsRegion": "us-west-2",
"eventTime": "2024-09-08T12:34:56.789Z",
"eventName": "ObjectCreated:Put",
"s3": {
"bucket": {
"name": "source-bucket-name"
},
"object": {
"key": "path/to/your/object.jpg",
"size": 12345
}
}
}
]
}

event['Records'][0]: This accesses the first record in the Records array of the event object. If various objects trigger the Lambda function simultaneously, but we are accessing the first one with [0].

event['Records'][0]['s3']['bucket']['name']:

event: The event data passed to the Lambda function.
[‘Records’]: The list of records contained in the event.
[0]: Accesses the first record in the list.
[‘s3’]: This part of the event object contains details about the S3 service.
[‘bucket’]: This nested JSON object contains bucket information that triggered the event.
[‘name’]: The name of the S3 bucket. This is where the object was created or modified.

The line source_bucket = event['Records'][0]['s3']['bucket']['name'] stores the name of the S3 bucket that triggered the event in the variable source_bucket.

event['Records'][0]['s3']['object']['key']:

[‘object’]: This nested JSON object contains details about the S3 object that triggered the event.
[‘key’]: The key (file path) of the S3 object that was created, modified, or deleted.

The line source_key = event['Records'][0]['s3']['object']['key'] stores the key (file path) of the object in the variable source_key.

{
  "Records": [
    {
      "s3": {
        "bucket": {
          "name": "my-image-bucket"
        },
        "object": {
          "key": "uploads/new_image.jpg"
        }
      }
    }
  ]
}

When the Lambda function executes:

source_bucket will be "my-image-bucket".
source_key will be "uploads/new_image.jpg".

This allows the Lambda function to identify which object triggered it and where it is located within the S3 bucket.

Note: You noticed a way to examine JSON content within the Lambda function. You can find the same way of accessing JSON data in the production projects.

3. API Gateway Integration: Fetching Data from a DynamoDB Table

This function is designed to be triggered by an API Gateway HTTP request to fetch data from a DynamoDB table.

import boto3
import json

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table('YourDynamoDBTableName')

def lambda_handler(event, context):
    # Fetching all items from DynamoDB table
    try:
        response = table.scan()
        items = response.get('Items', [])
        
        return {
            'statusCode': 200,
            'body': json.dumps(items)
        }
    
    except Exception as e:
        return {
            'statusCode': 500,
            'body': json.dumps({'error': str(e)})
        }