TTL with Streams for archival in DynamoDB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does TTL stand for in DynamoDB?

TTL stands for Time To Live. It is a feature that automatically deletes expired items from a DynamoDB table.

intermediate

How does DynamoDB Streams help with archival when using TTL?

DynamoDB Streams capture item changes, including deletions caused by TTL expiration. This allows you to archive deleted items by processing the stream before the data is lost.

intermediate

What is the typical flow for archiving data using TTL and Streams?

1. Enable TTL on the table to auto-delete expired items.
2. Enable DynamoDB Streams to capture deletions.
3. Use a Lambda function triggered by the stream to copy deleted items to an archive storage like S3.

advanced

Why is it important to process DynamoDB Streams quickly when using TTL for archival?

Because TTL deletes items automatically and the stream records are only kept for 24 hours, processing streams quickly ensures you capture and archive data before it disappears.

beginner

Can TTL be used to directly archive data in DynamoDB?

No, TTL only deletes expired items. Archival requires using DynamoDB Streams to capture deletions and then copying data to another storage system.

What happens to an item in DynamoDB when its TTL expires?

A It is marked as expired but remains in the table.

B It is archived automatically to S3.

C It is automatically deleted from the table.

D It triggers an alert but stays in the table.

TTL automatically deletes expired items from the DynamoDB table.

Which DynamoDB feature allows you to capture item deletions caused by TTL?

A DynamoDB Streams

B Global Secondary Index

C Provisioned Throughput

D DynamoDB Accelerator (DAX)

DynamoDB Streams capture all item changes including deletions caused by TTL.

What is a common service used to process DynamoDB Streams for archival?

A Amazon EC2

B AWS Lambda

C Amazon RDS

D AWS Glue

AWS Lambda is commonly used to process stream records and archive data.

How long are DynamoDB Stream records retained?

A 24 hours

B 7 days

C 30 days

D Indefinitely

Stream records are kept for 24 hours, so processing must be timely.

Which of the following is NOT true about TTL in DynamoDB?

A TTL deletes expired items automatically.

B TTL requires enabling DynamoDB Streams for archival.

C TTL helps manage data lifecycle by removing old data.

D TTL can trigger a Lambda function directly.

TTL does not trigger Lambda directly; Streams must be used to detect deletions.

Explain how TTL and DynamoDB Streams work together to enable data archival.

Think about how automatic deletion and event capture combine.

Describe the steps to set up a DynamoDB table for archival using TTL and Streams.

Consider configuration and processing flow.

Practice

1. What is the main purpose of enabling TTL (Time to Live) on a DynamoDB table?

easy

A. Increase read capacity units for faster queries

B. Encrypt data at rest for security

C. Create backups of the table automatically

D. Automatically delete expired items to keep the table clean

Solution

1. Step 1: Understand TTL function

   TTL marks items with an expiration timestamp so DynamoDB can delete them automatically after expiry.

2. Step 2: Identify TTL's main benefit

   This automatic deletion helps keep the table clean without manual intervention.

3. Final Answer:

   Automatically delete expired items to keep the table clean -> Option D

4. Quick Check:

   TTL = automatic deletion [OK]

Hint: TTL deletes expired data automatically [OK]

Common Mistakes:

• Confusing TTL with encryption
• Thinking TTL creates backups
• Assuming TTL increases capacity

2. Which of the following is the correct way to enable TTL on a DynamoDB table using AWS CLI?

easy

A. aws dynamodb enable-ttl --table MyTable --attribute expiryDate

B. aws dynamodb set-ttl --table-name MyTable --ttl-attribute expiryDate

C. aws dynamodb update-time-to-live --table-name MyTable --time-to-live-specification Enabled=true,AttributeName=expiryDate

D. aws dynamodb activate-ttl --table MyTable --attributeName expiryDate

Solution

1. Step 1: Recall AWS CLI TTL command

   The correct command is 'update-time-to-live' with parameters for table name and TTL specification.

2. Step 2: Match correct syntax

   aws dynamodb update-time-to-live --table-name MyTable --time-to-live-specification Enabled=true,AttributeName=expiryDate uses the exact syntax: --time-to-live-specification Enabled=true,AttributeName=expiryDate.

3. Final Answer:

   aws dynamodb update-time-to-live --table-name MyTable --time-to-live-specification Enabled=true,AttributeName=expiryDate -> Option C

4. Quick Check:

   Correct CLI command = aws dynamodb update-time-to-live --table-name MyTable --time-to-live-specification Enabled=true,AttributeName=expiryDate [OK]

Hint: Use 'update-time-to-live' with Enabled=true [OK]

Common Mistakes:

• Using non-existent commands like enable-ttl
• Wrong parameter names
• Missing 'time-to-live-specification' flag

3. Given a DynamoDB Stream enabled on a table with TTL, what type of event will appear in the stream when an item expires and is deleted?

medium

A. INSERT

B. REMOVE

C. MODIFY

D. UPDATE

Solution

1. Step 1: Understand TTL deletion effect on streams

   When TTL deletes an item, DynamoDB Streams capture this as a REMOVE event because the item is removed.

2. Step 2: Identify correct event type

   INSERT and MODIFY happen on new or updated items, not deletions. REMOVE is the correct event for deletions.

3. Final Answer:

   REMOVE -> Option B

4. Quick Check:

   TTL deletion = REMOVE event [OK]

Hint: TTL deletions trigger REMOVE events in streams [OK]

Common Mistakes:

• Choosing INSERT or MODIFY for deletions
• Confusing UPDATE with MODIFY
• Assuming TTL triggers no stream events

4. You wrote a Lambda function triggered by DynamoDB Streams to archive deleted items. However, the Lambda never receives any events for expired items. What is the most likely cause?

medium

A. The stream is not enabled or not set to capture REMOVE events

B. TTL is not enabled on the table

C. Lambda function has no permissions to read the table

D. The table has no primary key defined

Solution

1. Step 1: Check stream configuration

   If the Lambda never receives events, the stream might be disabled or not configured to capture REMOVE events, which TTL deletions generate.

2. Step 2: Verify other causes

   TTL must be enabled, but if streams are off or missing REMOVE events, Lambda won't get notifications. Permissions or missing primary key would cause other errors.

3. Final Answer:

   The stream is not enabled or not set to capture REMOVE events -> Option A

4. Quick Check:

   Missing REMOVE events in stream = The stream is not enabled or not set to capture REMOVE events [OK]

Hint: Ensure stream captures REMOVE events for TTL deletions [OK]

Common Mistakes:

• Ignoring stream settings
• Assuming permissions cause no events
• Overlooking TTL enablement

5. You want to archive expired DynamoDB items to S3 using a Lambda triggered by Streams. Which approach ensures no data loss and handles possible Lambda failures?

hard

A. Process REMOVE events in Lambda and write directly to S3, retrying on failure

B. Use TTL to delete items, ignore streams, and periodically scan table for expired items

C. Disable TTL and manually delete items after archiving

D. Process INSERT events in Lambda and archive items before expiration

Solution

1. Step 1: Understand archival with TTL and streams

   TTL deletes expired items, streams capture REMOVE events. Lambda triggered by these events can archive data safely.

2. Step 2: Ensure reliability and no data loss

   Processing REMOVE events and writing to S3 with retries ensures data is archived even if Lambda fails temporarily.

3. Step 3: Evaluate other options

   Use TTL to delete items, ignore streams, and periodically scan table for expired items ignores streams and risks missing data. Disable TTL and manually delete items after archiving disables TTL, losing automatic cleanup. Process INSERT events in Lambda and archive items before expiration archives before expiration, which is not TTL-based archival.

4. Final Answer:

   Process REMOVE events in Lambda and write directly to S3, retrying on failure -> Option A

5. Quick Check:

   Reliable archival = Process REMOVE events in Lambda and write directly to S3, retrying on failure [OK]

Hint: Archive REMOVE events with retries for safety [OK]

Common Mistakes:

• Ignoring stream REMOVE events
• Disabling TTL unnecessarily
• Archiving on INSERT instead of REMOVE