DynamoDB Streams concept - Mini Project: Build & Apply

DynamoDB Streams Concept

📖 Scenario: You are managing a simple inventory system for a small store. You want to keep track of changes made to the inventory items, such as when items are added, updated, or removed. DynamoDB Streams can help you capture these changes in real time.

🎯 Goal: Build a DynamoDB table with a stream enabled to capture item changes. Then, configure the stream to capture only the new images of changed items.

📋 What You'll Learn

Create a DynamoDB table named Inventory with a primary key ItemId of type string.

Enable DynamoDB Streams on the Inventory table.

Set the stream view type to NEW_IMAGE to capture only the new state of items after changes.

💡 Why This Matters

🌍 Real World

DynamoDB Streams help track changes in your database in real time, useful for audit logs, notifications, or syncing data to other systems.

💼 Career

Understanding DynamoDB Streams is important for backend developers and cloud engineers working with AWS to build scalable, event-driven applications.

1

Create the DynamoDB table

Create a DynamoDB table named Inventory with a primary key called ItemId of type string.

DynamoDB

# Your code here to create the Inventory table with ItemId as the primary key

Hint

Use the AWS CLI create-table command with the correct attribute definitions and key schema.

2

Enable DynamoDB Streams

Enable DynamoDB Streams on the Inventory table by updating the table to turn on streams.

DynamoDB

aws dynamodb create-table \
    --table-name Inventory \
    --attribute-definitions AttributeName=ItemId,AttributeType=S \
    --key-schema AttributeName=ItemId,KeyType=HASH \
    --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5
# Your code here to enable streams on the Inventory table

Hint

Use the AWS CLI update-table command with --stream-specification to enable streams.

3

Set the stream view type

Set the stream view type to NEW_IMAGE so the stream captures only the new images of items after changes.

DynamoDB

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

aws dynamodb update-table \
    --table-name Inventory \
    --stream-specification StreamEnabled=true,StreamViewType=NEW_IMAGE
# Your code here to confirm the stream view type is set to NEW_IMAGE

Hint

Use describe-table to check the stream settings.

4

Complete the DynamoDB Streams setup

Complete the setup by confirming the stream ARN is available in the table description.

DynamoDB

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

aws dynamodb update-table \
    --table-name Inventory \
    --stream-specification StreamEnabled=true,StreamViewType=NEW_IMAGE

aws dynamodb describe-table --table-name Inventory
# Your code here to confirm the stream ARN is present

Hint

Look for LatestStreamArn in the table description output to confirm streams are enabled.

Practice

1. What is the primary purpose of DynamoDB Streams?

easy

A. To back up the entire DynamoDB table automatically every hour

B. To capture and record changes made to items in a DynamoDB table in real time

C. To increase the read capacity of a DynamoDB table

D. To encrypt data stored in DynamoDB tables

Solution

1. Step 1: Understand DynamoDB Streams functionality

   DynamoDB Streams capture data changes such as inserts, updates, and deletes on a table.

2. Step 2: Compare options with Streams purpose

   Only To capture and record changes made to items in a DynamoDB table in real time describes capturing changes in real time, which is the core function of Streams.

3. Final Answer:

   To capture and record changes made to items in a DynamoDB table in real time -> Option B

4. Quick Check:

   DynamoDB Streams = capture changes [OK]

Hint: Streams track table changes live, not backups or capacity [OK]

Common Mistakes:

• Confusing Streams with backups
• Thinking Streams increase capacity
• Assuming Streams encrypt data

2. Which of the following is the correct way to enable DynamoDB Streams on a table?

easy

A. Enable Auto Scaling on the table

B. Add a Global Secondary Index with StreamEnabled = true

C. Create a Lambda function and attach it to the table without enabling Streams

D. Set the StreamSpecification with StreamEnabled = true and choose a StreamViewType

Solution

1. Step 1: Recall how to enable Streams

   Streams are enabled by setting StreamSpecification with StreamEnabled true and selecting a StreamViewType.

2. Step 2: Evaluate options

   Set the StreamSpecification with StreamEnabled = true and choose a StreamViewType correctly describes enabling Streams. Other options relate to indexes, Lambda, or scaling, which do not enable Streams.

3. Final Answer:

   Set the StreamSpecification with StreamEnabled = true and choose a StreamViewType -> Option D

4. Quick Check:

   Enable Streams = StreamSpecification true + StreamViewType [OK]

Hint: Enable Streams by setting StreamSpecification true with view type [OK]

Common Mistakes:

• Confusing Streams with indexes
• Assuming Lambda enables Streams automatically
• Thinking Auto Scaling enables Streams

3. Given a DynamoDB Stream with StreamViewType set to NEW_AND_OLD_IMAGES, what data will each stream record contain?

medium

A. Only the new image of the item after the change

B. Only the old image of the item before the change

C. Both the new and old images of the item

D. Only the keys of the changed item

Solution

1. Step 1: Understand StreamViewType NEW_AND_OLD_IMAGES

   This view type captures both the item image before and after the change.

2. Step 2: Match options to the view type

   Both the new and old images of the item correctly states both new and old images are included. Other options only mention one or keys.

3. Final Answer:

   Both the new and old images of the item -> Option C

4. Quick Check:

   NEW_AND_OLD_IMAGES = new + old images [OK]

Hint: NEW_AND_OLD_IMAGES means both before and after data included [OK]

Common Mistakes:

• Thinking only new or only old image is included
• Confusing keys-only view with full images
• Ignoring the StreamViewType setting

4. You have enabled DynamoDB Streams but your Lambda function is not receiving any events despite recent writes to the table. What is a possible reason?

medium

A. The Lambda function is not properly configured as an event source for the stream

B. The table has no write activity, so no stream records are generated

C. All of the above

D. The StreamViewType was set to KEYS_ONLY, but your Lambda expects full images

Solution

1. Step 1: Analyze the scenario

   Streams enabled with recent writes means records are generated, so issue is likely with Lambda setup to consume stream events.

2. Step 2: Evaluate options

   The Lambda not being configured as an event source for the stream explains no events. All of the above doesn't apply since writes occurred. No write activity contradicted by scenario. StreamViewType affects record content, not event delivery to Lambda.

3. Final Answer:

   The Lambda function is not properly configured as an event source for the stream -> Option A

4. Quick Check:

   No events despite writes = Lambda event source not mapped [OK]

Hint: Lambda must be mapped as event source to DynamoDB Stream [OK]

Common Mistakes:

• Ignoring that no writes means no stream records
• Forgetting to attach Lambda as event source
• Assuming KEYS_ONLY always sends full data

5. You want to build a system that reacts only when an item's attribute status changes in your DynamoDB table. Which StreamViewType should you choose to efficiently detect this change?

hard

A. NEW_AND_OLD_IMAGES

B. OLD_IMAGE

C. NEW_IMAGE

D. KEYS_ONLY

Solution

1. Step 1: Identify data needed to detect attribute changes

   To know if 'status' changed, you need both old and new values to compare.

2. Step 2: Match StreamViewType to requirement

   Only NEW_AND_OLD_IMAGES provides both before and after images for comparison.

3. Final Answer:

   NEW_AND_OLD_IMAGES -> Option A

4. Quick Check:

   Detect attribute change = need old + new images [OK]

Hint: Compare old and new images to detect attribute changes [OK]

Common Mistakes:

• Choosing only NEW_IMAGE or OLD_IMAGE which lacks comparison data
• Assuming KEYS_ONLY includes attribute data
• Not realizing both images are needed to detect changes