Lambda function that generates a thumbnail for any image file uploaded to S3.

thumbnail_generator_lambda.py

import os
import json
import boto3
from PIL import Image
import pathlib
import urllib

# Read from environmental variables
ID = os.environ['AWS_ID']
KEY = os.environ['AWS_KEY']
REGION = os.environ['AWS_REGION']
BUCKET = os.environ['BUCKET_NAME']

def lambda_handler(event, context):
    # Init S3 Client
    client = boto3.client(
        's3',
        aws_access_key_id=ID,
        aws_secret_access_key=KEY,
        region_name=REGION
    )
    for record in event['Records']:
        # Read new file (S3 Event: it will always contain one element). Each new file will generate a new event and a new Lambda will be called.
        image_path = record['s3']['object']['key']
        # Format string to a path that can be read by Boto3
        image_path = urllib.parse.unquote_plus(image_path)
    
        lambda_download_path =  f"/tmp/{pathlib.Path(image_path).name}" # Local path to download the new file.
        lambda_new_file_path = f"/tmp/{get_new_file_name(image_path)}" # Local path in which to create the new file (thumbnail).
        s3_new_file_path = f"thumbnails/{get_new_file_name(image_path)}" # S3 path in which to upload the new file (thumbnail)
    
        # Download new file to Lambda local
        client.download_file(BUCKET, image_path, lambda_download_path)
       
        # Read the new file and generate the thumbnail
        image = Image.open(lambda_download_path)
        MAX_SIZE = (200, 200)
        image.thumbnail(MAX_SIZE)
        image.save(lambda_new_file_path)
        
        # Upload the thumbnail to S3
        client.upload_file(lambda_new_file_path, BUCKET,s3_new_file_path)
        print(f'New file uploaded to path {s3_new_file_path}')
    
    return {
        'statusCode': 200,
        'body': json.dumps(s3_new_file_path)
    }
    
    
def get_new_file_name(file_name):
    # Takes the file passed as parameter and adds the suffix 'thumbnail' before the file format.
    file_extension  = pathlib.Path(file_name).suffix
    file_name = pathlib.Path(file_name).stem
    return f"{file_name}_thumbnail{file_extension}"