Creating an AWS Lambda Price Checker with SNS E-mail Notifications

November 27, 2024

Using an AWS lambda to check the price of item and get informed when it drops under a certain threshold by e-mail

This tutorial guides you through creating an AWS Lambda function to monitor product prices on Amazon and send alerts when the price drops below a predefined threshold. Notifications will be sent via AWS SNS, per e-mail.

The entire setup will incur no additional cost, it is well within the AWS free tier.

Prerequisites:

AWS Account with access to AWS Lambda, EventBridge and SNS.

The Lambda Function

Below is the Python code for the Lambda function:

import json
import requests
import re
from bs4 import BeautifulSoup
import boto3  # For SNS notifications

# Function to handle the Lambda event
def lambda_handler(event, context):
    # Define the product to monitor
    products = [
        {
            "url": 'https://www.amazon.de/-/en/AMD-Ryzen-7800X3D-Technology-Architecture/dp/B0BTZB7F88/',
            "name": "AMD Ryzen 7 7800X3D",
            "threshold": 600.0  # Price threshold in Euros
        }
    ]

    messages = []

    for product in products:
        price = check_price_amazon(product["url"])

        if price is not None and price < product["threshold"]:
            # Send notification
            send_sns_notification(price, product["url"], product["name"])
            messages.append(f'Price for {product["name"]} dropped to {price} EUR! Notification sent.')
        else:
            messages.append(f'Price for {product["name"]} is still above the threshold.')

    return {
        'statusCode': 200,
        'body': json.dumps(' '.join(messages))
    }

# Function to check the price on Amazon
def check_price_amazon(url):
    HEADERS = {
        "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:89.0) Gecko/20100101 Firefox/89.0",
        "Accept-Language": "en-US,en;q=0.9",
        "Accept-Encoding": "gzip, deflate, br",
        "Connection": "keep-alive"
    }

    try:
        response = requests.get(url, headers=HEADERS, timeout=10)
        if response.status_code == 200:
            soup = BeautifulSoup(response.content, 'html.parser')
            price_whole = soup.find('span', {'class': 'a-price-whole'})
            price_fraction = soup.find('span', {'class': 'a-price-fraction'})
            if price_whole and price_fraction:
                # Clean the price string by removing non-numeric characters
                price_whole_cleaned = re.sub(r'[^\d]', '', price_whole.text)
                price_fraction_cleaned = re.sub(r'[^\d]', '', price_fraction.text)

                # Combine whole and fractional parts into a valid float
                price = float(f"{price_whole_cleaned}.{price_fraction_cleaned}")
                return price
        elif response.status_code == 503:
            print("Server returned 503. Possible bot detection.")
    except requests.exceptions.RequestException as e:
        print(f"Request failed: {e}")
    return None

# Function to send a notification via AWS SNS
def send_sns_notification(price, product_url, product_name):
    sns_client = boto3.client('sns')
    topic_arn = 'SNS_TOPIC_ARN'  # Replace with your SNS Topic ARN

    message = f"The price for {product_name} has dropped to {price} EUR. Check it out here: {product_url}"
    response = sns_client.publish(
        TopicArn=topic_arn,
        Message=message,
        Subject="Price Alert!"
    )
    print(f"SNS notification sent with response: {response}")

Configuration

1. Set Lambda Timeout

Set the Lambda timeout to 10 seconds:
- Open the Lambda function in the AWS Console.
- Go to Configuration > General Configuration.
- Set Timeout to 10 seconds.

2. Add Layers to the lambda

Add the following layers for requests and BeautifulSoup. Use the appropriate Python runtime version and region-specific ARNs from the Klayers repository.

3. Add SNS Permissions to Lambda Role

Open the IAM Role assigned to your Lambda function and add the SNS publish to it:

4. Set Up SNS

Step 1: Go to the SNS Console.
Step 2: Create a new standard topic.
- Sub-step: Provide a unique name.
- Sub-step: Copy the Topic ARN and replace SNS_TOPIC_ARN in the Lambda code with it.
Step 3: Configure subscriptions.
- Create a new subscription to the SNS Topic.
- Choose Email as the protocol and provide your email address.
- Confirm the subscription via the confirmation email.

5. Add an EventBridge Trigger to the Lambda

Configure an EventBridge Rule to trigger the Lambda periodically (daily in the example):

6. Testing the Lambda function:

Open the Lambda test console and use an empty json event.

Execute the function and verify the subscribed email.

7. Results:

WHEN AND IF the price of your item/items drops bellow the set threshold, you will receive a mail like this: