Why change tracking enables reactions in DynamoDB - See It in Action

Why Change Tracking Enables Reactions in DynamoDB

📖 Scenario: You are managing a simple online store's inventory using DynamoDB. You want to track changes in product stock levels so that when stock is low, the system can react by sending alerts or triggering restock processes automatically.

🎯 Goal: Build a DynamoDB table with product data, configure a change tracking mechanism using DynamoDB Streams, and write a query to detect stock changes that trigger reactions.

📋 What You'll Learn

Create a DynamoDB table named Products with specific product entries

Enable DynamoDB Streams on the Products table to track changes

Write a query to detect when product stock falls below a threshold

Set up a reaction trigger based on the detected stock changes

💡 Why This Matters

🌍 Real World

Tracking inventory changes in real time helps businesses react quickly to low stock and avoid running out of products.

💼 Career

Understanding change tracking and reactions in DynamoDB is valuable for roles in cloud development, DevOps, and backend engineering.

1

Create the Products table with initial data

Create a DynamoDB table called Products with these exact items: {"ProductID": "P001", "Name": "Notebook", "Stock": 50}, {"ProductID": "P002", "Name": "Pen", "Stock": 100}, and {"ProductID": "P003", "Name": "Eraser", "Stock": 30}.

DynamoDB

# Your code here to create the Products table and add the three items

Need a hint?

Use aws dynamodb create-table to create the table and aws dynamodb put-item to add each product.

2

Enable DynamoDB Streams for change tracking

Enable DynamoDB Streams on the Products table with the stream view type set to NEW_AND_OLD_IMAGES to track changes before and after updates.

DynamoDB

aws dynamodb create-table --table-name Products --attribute-definitions AttributeName=ProductID,AttributeType=S --key-schema AttributeName=ProductID,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

aws dynamodb put-item --table-name Products --item '{"ProductID": {"S": "P001"}, "Name": {"S": "Notebook"}, "Stock": {"N": "50"}}'
aws dynamodb put-item --table-name Products --item '{"ProductID": {"S": "P002"}, "Name": {"S": "Pen"}, "Stock": {"N": "100"}}'
aws dynamodb put-item --table-name Products --item '{"ProductID": {"S": "P003"}, "Name": {"S": "Eraser"}, "Stock": {"N": "30"}}'
# Your code here to enable DynamoDB Streams with NEW_AND_OLD_IMAGES

Need a hint?

Use aws dynamodb update-table with --stream-specification to enable streams.

3

Query to detect low stock changes

Write a DynamoDB query or scan command that filters products where the Stock attribute is less than 20 to detect low stock levels.

DynamoDB

aws dynamodb create-table --table-name Products --attribute-definitions AttributeName=ProductID,AttributeType=S --key-schema AttributeName=ProductID,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

aws dynamodb put-item --table-name Products --item '{"ProductID": {"S": "P001"}, "Name": {"S": "Notebook"}, "Stock": {"N": "50"}}'
aws dynamodb put-item --table-name Products --item '{"ProductID": {"S": "P002"}, "Name": {"S": "Pen"}, "Stock": {"N": "100"}}'
aws dynamodb put-item --table-name Products --item '{"ProductID": {"S": "P003"}, "Name": {"S": "Eraser"}, "Stock": {"N": "30"}}'

aws dynamodb update-table --table-name Products --stream-specification StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES
# Your code here to query products with Stock less than 20

Need a hint?

Use aws dynamodb scan with a filter expression to find products with stock less than 20.

4

Set up reaction trigger for low stock

Configure a reaction by creating a Lambda function trigger on the DynamoDB Stream of the Products table that activates when stock falls below 20. Write the Lambda function code snippet that checks the Stock attribute in the stream event and triggers an alert if stock is low.

DynamoDB

aws dynamodb create-table --table-name Products --attribute-definitions AttributeName=ProductID,AttributeType=S --key-schema AttributeName=ProductID,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

aws dynamodb put-item --table-name Products --item '{"ProductID": {"S": "P001"}, "Name": {"S": "Notebook"}, "Stock": {"N": "50"}}'
aws dynamodb put-item --table-name Products --item '{"ProductID": {"S": "P002"}, "Name": {"S": "Pen"}, "Stock": {"N": "100"}}'
aws dynamodb put-item --table-name Products --item '{"ProductID": {"S": "P003"}, "Name": {"S": "Eraser"}, "Stock": {"N": "30"}}'

aws dynamodb update-table --table-name Products --stream-specification StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES

aws dynamodb scan --table-name Products --filter-expression "Stock < :val" --expression-attribute-values '{":val":{"N":"20"}}'
# Your code here to write a Lambda function snippet that triggers on stream events and checks stock

Need a hint?

Write a Lambda function that loops over stream records, checks for MODIFY events, reads the new stock value, and triggers an alert if stock is below 20.