DynamoDB Streams overview in AWS - Step-by-Step Execution

Process Flow - DynamoDB Streams overview

Data change in DynamoDB table

↓

DynamoDB Streams captures change

↓

Stream records created

↓

Stream consumer reads records

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Consumer processes changes

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End

When data changes in a DynamoDB table, Streams capture these changes as records. A consumer reads and processes these records to react to the changes.

Execution Sample

AWS

1. Write item to DynamoDB table
2. DynamoDB Streams captures this write
3. Stream record created with change details
4. Consumer reads stream record
5. Consumer processes the change

This sequence shows how a data write triggers a stream record that a consumer reads and processes.

Process Table

Step	Action	Stream Record Created?	Consumer Reads?	Consumer Processes?
1	Write item to DynamoDB table	No	No	No
2	DynamoDB Streams captures change	Yes	No	No
3	Stream record available	Yes	No	No
4	Consumer reads stream record	Yes	Yes	No
5	Consumer processes the change	Yes	Yes	Yes
6	No new changes	No	No	No

💡 No new changes in DynamoDB, so no new stream records or processing

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 4	After Step 5	Final
DynamoDB Table Data	Empty	Item added	Item added	Item added	Item added	Item added
Stream Records	Empty	Empty	One record created	One record read	One record processed	One record processed
Consumer State	Idle	Idle	Idle	Reading	Processing	Idle

Key Moments - 3 Insights

Why doesn't the consumer process anything immediately after the item is written?

Because the stream record is created only after the write completes (see Step 2 and 3 in execution_table). The consumer reads and processes only after the record exists.

Can the consumer read stream records before they are created?

No, the consumer can only read records after DynamoDB Streams captures the change and creates the record (Step 3).

What happens if no data changes occur in the table?

No new stream records are created, so the consumer has nothing to read or process (Step 6).

Visual Quiz - 3 Questions

Look at the execution_table, at which step does the stream record get created?

A Step 1

B Step 2

C Step 4

D Step 5

💡 Hint

Check the 'Stream Record Created?' column in execution_table

According to variable_tracker, what is the consumer state after Step 4?

A Reading

B Processing

C Idle

D Waiting

💡 Hint

Look at the 'Consumer State' row and the 'After Step 4' column

If no new data changes happen, what happens to the stream records and consumer processing?

A New stream records are created and processed

B Consumer processes old records repeatedly

C No new stream records, consumer remains idle

D Stream records are deleted automatically

💡 Hint

Refer to Step 6 in execution_table and final states in variable_tracker

Concept Snapshot

DynamoDB Streams capture table data changes as records.
Each change (insert, update, delete) creates a stream record.
Consumers read these records to react to changes.
Stream records appear shortly after data changes.
No changes mean no new stream records or processing.

Full Transcript

DynamoDB Streams work by capturing changes made to a DynamoDB table. When you write, update, or delete an item, the stream records this change. These records are then available for a consumer application to read and process. The flow starts with a data change, followed by stream record creation, then the consumer reads and processes the record. If no changes happen, no new stream records are created, and the consumer remains idle. This process helps applications react to data changes in near real-time.

Practice

1. What is the main purpose of DynamoDB Streams?

easy

A. To store backups of DynamoDB tables permanently

B. To encrypt data stored in DynamoDB tables

C. To increase the read capacity of a DynamoDB table

D. To track and react to data changes in real time

Solution

1. Step 1: Understand DynamoDB Streams function

   DynamoDB Streams capture data changes like inserts, updates, and deletes in real time.

2. Step 2: Compare options with Streams purpose

   Only To track and react to data changes in real time correctly describes tracking and reacting to data changes. Other options describe unrelated features.

3. Final Answer:

   To track and react to data changes in real time -> Option D

4. Quick Check:

   DynamoDB Streams = Track data changes [OK]

Hint: Streams capture table changes instantly for reaction [OK]

Common Mistakes:

• Confusing Streams with backup or encryption features
• Thinking Streams increase read capacity
• Assuming Streams store data permanently

2. Which setting must be enabled to start using DynamoDB Streams on a table?

easy

A. EncryptionEnabled set to true

B. BackupEnabled set to true

C. StreamEnabled set to true

D. AutoScalingEnabled set to true

Solution

1. Step 1: Identify the configuration for enabling Streams

   To use DynamoDB Streams, the table must have StreamEnabled set to true.

2. Step 2: Eliminate unrelated settings

   BackupEnabled, EncryptionEnabled, and AutoScalingEnabled do not enable Streams.

3. Final Answer:

   StreamEnabled set to true -> Option C

4. Quick Check:

   Enable Streams = StreamEnabled true [OK]

Hint: Enable Streams by setting StreamEnabled true [OK]

Common Mistakes:

• Confusing Streams with backups or encryption
• Assuming AutoScaling enables Streams
• Forgetting to enable Streams explicitly

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

medium

A. Only the new item image after the change

B. Both the new and old item images

C. Only the keys of the changed items

D. Only the old item image before the change

Solution

1. Step 1: Understand StreamViewType NEW_AND_OLD_IMAGES meaning

   This setting records both the item before and after the change.

2. Step 2: Compare options with StreamViewType behavior

   Only Both the new and old item images matches the behavior of capturing both new and old images.

3. Final Answer:

   Both the new and old item images -> Option B

4. Quick Check:

   NEW_AND_OLD_IMAGES = new + old data [OK]

Hint: NEW_AND_OLD_IMAGES means capture before and after data [OK]

Common Mistakes:

• Choosing only new or only old images
• Confusing keys only with full images
• Not knowing StreamViewType options

4. A developer enabled DynamoDB Streams but does not see any stream records after table updates. What is the most likely cause?

medium

A. StreamEnabled is false on the table

B. StreamViewType is set to KEYS_ONLY

C. Stream retention period is set to 7 days

D. The table has no primary key defined

Solution

1. Step 1: Check if Streams are enabled

   If StreamEnabled is false, no stream records are generated regardless of updates.

2. Step 2: Evaluate other options

   KEYS_ONLY still produces records; retention period (24-168 hours) does not prevent seeing recent records; tables require primary keys but that doesn't stop streams if enabled.

3. Final Answer:

   StreamEnabled is false on the table -> Option A

4. Quick Check:

   No records = Streams not enabled [OK]

Hint: Streams must be enabled to see records [OK]

Common Mistakes:

• Assuming KEYS_ONLY disables records
• Thinking retention period prevents seeing records
• Ignoring StreamEnabled setting

5. You want to trigger a Lambda function whenever an item is updated in your DynamoDB table to process both the old and new item images. Which DynamoDB Streams configuration and setup is required?

hard

A. Enable Streams with StreamViewType NEW_AND_OLD_IMAGES and configure Lambda trigger on the stream

B. Enable Streams with StreamViewType KEYS_ONLY and configure Lambda trigger on the table

C. Enable Streams with StreamViewType NEW_IMAGE and configure Lambda trigger on the stream

D. Enable Streams with StreamViewType OLD_IMAGE and configure Lambda trigger on the table

Solution

1. Step 1: Choose StreamViewType for updates

   To capture both before and after update data, use NEW_AND_OLD_IMAGES.

2. Step 2: Configure Lambda trigger on the DynamoDB Stream

   Lambda triggers must be set on the stream, not directly on the table.

3. Final Answer:

   Enable Streams with StreamViewType NEW_AND_OLD_IMAGES and configure Lambda trigger on the stream -> Option A

4. Quick Check:

   Lambda trigger on stream with NEW_AND_OLD_IMAGES [OK]

Hint: Use NEW_AND_OLD_IMAGES and trigger Lambda on stream [OK]

Common Mistakes:

• Triggering Lambda directly on table instead of stream
• Choosing KEYS_ONLY or OLD_IMAGE for update data
• Not enabling Streams before Lambda trigger