Event-driven architecture patterns in DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an event in event-driven architecture?

An event is a significant change or action that happens in a system, like a new order placed or a user signed up. It triggers other parts of the system to react.

intermediate

How does DynamoDB Streams support event-driven architecture?

DynamoDB Streams captures data changes in a table and sends them as events, allowing other services to react to these changes in real time.

beginner

What is the role of an event processor in event-driven systems?

An event processor listens for events and performs actions based on those events, like updating data or triggering workflows.

intermediate

Explain the difference between event-driven and request-driven architectures.

Event-driven architecture reacts to events asynchronously, while request-driven waits for direct requests and responds immediately.

beginner

Why is decoupling important in event-driven architecture?

Decoupling means parts of the system work independently, so changes in one part don’t break others. It makes the system flexible and easier to maintain.

What does DynamoDB Streams capture?

A Network traffic logs

B User login events

C Changes to items in a DynamoDB table

D Scheduled backups

DynamoDB Streams captures changes to items in a DynamoDB table as events.

In event-driven architecture, what triggers an action?

A An event

B A direct user request

C A scheduled timer

D A database backup

Actions are triggered by events, which represent changes or significant occurrences.

Which of these is a benefit of decoupling in event-driven systems?

A Tighter integration

B Easier maintenance

C More complex dependencies

D Slower response times

Decoupling makes systems easier to maintain by reducing dependencies.

What is an event processor responsible for?

A Managing user authentication

B Storing data permanently

C Generating user reports

D Listening and reacting to events

Event processors listen for events and perform actions based on them.

How does event-driven architecture handle communication?

A Asynchronously through events

B Synchronously through direct calls

C Only through user input

D By polling databases continuously

Event-driven architecture uses asynchronous communication via events.

Describe how DynamoDB Streams can be used in an event-driven architecture.

Think about how changes in the database can trigger other actions.

Explain why decoupling is important in event-driven systems and how it benefits system design.

Consider how parts of the system work without tightly depending on each other.

Practice

1. What is the main purpose of using DynamoDB Streams in an event-driven architecture?

easy

A. To capture and record changes in the DynamoDB table as events

B. To store backup copies of the DynamoDB table

C. To increase the read capacity of the DynamoDB table

D. To encrypt data stored in DynamoDB

Solution

1. Step 1: Understand DynamoDB Streams role

   DynamoDB Streams capture data modification events like inserts, updates, and deletes.

2. Step 2: Identify the purpose in event-driven architecture

   These captured events trigger other processes automatically, enabling real-time reactions.

3. Final Answer:

   To capture and record changes in the DynamoDB table as events -> Option A

4. Quick Check:

   DynamoDB Streams = capture changes [OK]

Hint: Streams capture table changes as events for triggers [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 using AWS CLI?

easy

A. aws dynamodb set-stream --table MyTable --enabled true

B. aws dynamodb enable-stream --table MyTable --type NEW_IMAGE

C. aws dynamodb create-stream --table-name MyTable --view-type KEYS_ONLY

D. aws dynamodb update-table --table-name MyTable --stream-specification StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES

Solution

1. Step 1: Recall AWS CLI command for enabling streams

   The correct command uses 'update-table' with '--stream-specification' to enable streams.

2. Step 2: Verify syntax and parameters

   aws dynamodb update-table --table-name MyTable --stream-specification StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES correctly sets StreamEnabled=true and specifies StreamViewType as NEW_AND_OLD_IMAGES.

3. Final Answer:

   aws dynamodb update-table --table-name MyTable --stream-specification StreamEnabled=true,StreamViewType=NEW_AND_OLD_IMAGES -> Option D

4. Quick Check:

   Enable streams = update-table + stream-specification [OK]

Hint: Use update-table with stream-specification to enable streams [OK]

Common Mistakes:

• Using non-existent commands like enable-stream
• Incorrect parameter names
• Confusing create-stream with enabling streams

3. Given a DynamoDB Stream enabled with StreamViewType=NEW_IMAGE, what will an AWS Lambda function receive when an item is updated?

medium

A. Only the keys of the updated item

B. The entire item before and after the update

C. Only the new version of the item after the update

D. No data, only a notification that an update occurred

Solution

1. Step 1: Understand StreamViewType NEW_IMAGE meaning

   NEW_IMAGE sends only the new version of the item after the change.

2. Step 2: Determine what Lambda receives on update

   Lambda gets the updated item data, not the old version or just keys.

3. Final Answer:

   Only the new version of the item after the update -> Option C

4. Quick Check:

   NEW_IMAGE = new item data only [OK]

Hint: NEW_IMAGE sends only updated item data to Lambda [OK]

Common Mistakes:

• Confusing NEW_IMAGE with NEW_AND_OLD_IMAGES
• Assuming keys only are sent
• Thinking Lambda gets no data

4. You wrote a Lambda function triggered by DynamoDB Streams but it never executes. What is the most likely cause?

medium

A. The DynamoDB table does not have Streams enabled

B. The Lambda function is not subscribed to the stream

C. The Lambda function code has syntax errors

D. The DynamoDB table has no data

Solution

1. Step 1: Check if Streams are enabled

   If Streams were not enabled, no events would be generated, but question implies setup.

2. Step 2: Verify Lambda subscription to the stream

   Without subscribing Lambda to the stream, it won't trigger on events.

3. Final Answer:

   The Lambda function is not subscribed to the stream -> Option B

4. Quick Check:

   Lambda must be subscribed to stream to trigger [OK]

Hint: Ensure Lambda is subscribed to DynamoDB Stream [OK]

Common Mistakes:

• Assuming syntax errors stop invocation
• Thinking empty table stops Lambda trigger
• Ignoring subscription setup

5. You want to build a real-time notification system using DynamoDB and Lambda. Which event-driven architecture pattern best fits this use case?

hard

A. Use DynamoDB Streams to capture changes and trigger Lambda to send notifications

B. Use periodic polling of DynamoDB to check for changes and send notifications

C. Use DynamoDB Global Tables to replicate data and notify users

D. Use DynamoDB backups to trigger notifications on data changes

Solution

1. Step 1: Identify real-time event-driven pattern

   Real-time notifications require immediate reaction to data changes.

2. Step 2: Match pattern with DynamoDB Streams and Lambda

   Streams capture changes as events; Lambda processes them instantly to notify users.

3. Final Answer:

   Use DynamoDB Streams to capture changes and trigger Lambda to send notifications -> Option A

4. Quick Check:

   Streams + Lambda = real-time notifications [OK]

Hint: Streams trigger Lambda for instant notifications [OK]

Common Mistakes:

• Choosing polling which is not real-time
• Confusing replication with notifications
• Using backups which are not event triggers