Time to live (TTL) for expiration in AWS - Mini Project: Build & Apply

Time to live (TTL) for expiration

📖 Scenario: You are managing a cloud database where data should automatically expire after a certain time to save space and keep information fresh.Imagine a library where books are borrowed and must be returned after a fixed period. Similarly, data entries will have a 'time to live' (TTL) that tells the system when to delete them.

🎯 Goal: Create a DynamoDB table with a TTL attribute that automatically deletes expired items.

📋 What You'll Learn

Create a DynamoDB table named LibraryBooks with a primary key BookID of type string.

Add a TTL attribute named ExpirationTime to the table configuration.

Set the TTL attribute to enable automatic expiration of items.

Use AWS CloudFormation syntax for the configuration.

💡 Why This Matters

🌍 Real World

TTL is used in cloud databases to automatically remove outdated data, saving storage and improving performance.

💼 Career

Understanding TTL configuration is important for cloud engineers and architects managing scalable, cost-efficient databases.

1

Create DynamoDB table resource

Create a DynamoDB table resource named LibraryBooks with a primary key attribute BookID of type String in AWS CloudFormation YAML syntax.

AWS

# Your code here to create the DynamoDB table resource

Hint

Define the DynamoDB table with Type: AWS::DynamoDB::Table. Use AttributeDefinitions and KeySchema to set the primary key.

2

Add TTL attribute name configuration

Add a TimeToLiveSpecification property to the LibraryBooks resource with AttributeName set to ExpirationTime.

AWS

Resources:
  LibraryBooks:
    Type: AWS::DynamoDB::Table
    Properties:
      TableName: LibraryBooks
      AttributeDefinitions:
        - AttributeName: BookID
          AttributeType: S
      KeySchema:
        - AttributeName: BookID
          KeyType: HASH
      BillingMode: PAY_PER_REQUEST
# Add TimeToLiveSpecification with AttributeName ExpirationTime here

Hint

Use TimeToLiveSpecification inside Properties to specify the TTL attribute name.

3

Enable TTL for the attribute

Add Enabled: true inside the TimeToLiveSpecification property to activate TTL on the ExpirationTime attribute.

AWS

Resources:
  LibraryBooks:
    Type: AWS::DynamoDB::Table
    Properties:
      TableName: LibraryBooks
      AttributeDefinitions:
        - AttributeName: BookID
          AttributeType: S
      KeySchema:
        - AttributeName: BookID
          KeyType: HASH
      BillingMode: PAY_PER_REQUEST
      TimeToLiveSpecification:
        AttributeName: ExpirationTime
# Enable TTL by setting Enabled to true here

Hint

Set Enabled to true to turn on TTL for the attribute.

4

Complete the CloudFormation template

Add the ExpirationTime attribute to AttributeDefinitions with type Number to store the TTL timestamp.

AWS

Resources:
  LibraryBooks:
    Type: AWS::DynamoDB::Table
    Properties:
      TableName: LibraryBooks
      AttributeDefinitions:
        - AttributeName: BookID
          AttributeType: S
# Add ExpirationTime attribute definition with type Number here
      KeySchema:
        - AttributeName: BookID
          KeyType: HASH
      BillingMode: PAY_PER_REQUEST
      TimeToLiveSpecification:
        AttributeName: ExpirationTime
        Enabled: true

Hint

TTL attribute must be defined as a Number type in AttributeDefinitions.

Practice

1. What is the main purpose of Time to Live (TTL) in AWS DynamoDB?

easy

A. Backup data to another region

B. Encrypt data at rest for security

C. Automatically delete expired items to save storage space

D. Increase read capacity for faster queries

Solution

1. Step 1: Understand TTL function

   TTL is designed to remove items automatically after a set expiration time.

2. Step 2: Identify the main benefit

   This automatic deletion helps save storage space and reduces manual cleanup.

3. Final Answer:

   Automatically delete expired items to save storage space -> Option C

4. Quick Check:

   TTL purpose = automatic deletion [OK]

Hint: TTL deletes expired data automatically to save space [OK]

Common Mistakes:

• Confusing TTL with encryption
• Thinking TTL backs up data
• Assuming TTL improves query speed

2. Which attribute type must the TTL attribute have in DynamoDB to enable expiration?

easy

A. Number representing Unix epoch time in seconds

B. Binary data with expiration timestamp

C. Boolean indicating expired or not

D. String containing date in ISO format

Solution

1. Step 1: Check TTL attribute requirements

   DynamoDB TTL requires a Number attribute representing expiration time as Unix epoch seconds.

2. Step 2: Eliminate other types

   String, Boolean, or Binary types are not valid for TTL expiration timestamps.

3. Final Answer:

   Number representing Unix epoch time in seconds -> Option A

4. Quick Check:

   TTL attribute = Number (epoch seconds) [OK]

Hint: TTL attribute must be a number with epoch seconds [OK]

Common Mistakes:

• Using string dates instead of numbers
• Setting TTL attribute as Boolean
• Trying to use binary data for TTL

3. Given this DynamoDB item with TTL attribute expireAt: 1700000000 (Unix epoch seconds), what happens when current time is 1700000001?

medium

A. Item remains until manually deleted

B. Item's TTL attribute is reset to current time

C. Item is archived to S3 automatically

D. Item is immediately deleted by DynamoDB TTL process

Solution

1. Step 1: Compare current time with TTL value

   The current time (1700000001) is greater than the TTL attribute (1700000000), so the item is expired.

2. Step 2: Understand TTL behavior on expiration

   DynamoDB TTL automatically deletes expired items shortly after expiration time passes.

3. Final Answer:

   Item is immediately deleted by DynamoDB TTL process -> Option D

4. Quick Check:

   Current time > TTL = item deleted [OK]

Hint: Item deletes soon after TTL time passes [OK]

Common Mistakes:

• Thinking TTL deletes instantly at exact second
• Assuming manual deletion is needed
• Believing TTL archives data instead of deleting

4. You enabled TTL on attribute expiry but items are not deleting after expiration. What is the most likely cause?

medium

A. DynamoDB table is in a different region

B. TTL attribute expiry is missing or has wrong data type

C. TTL only works on primary key attributes

D. TTL requires manual activation every 24 hours

Solution

1. Step 1: Check TTL attribute correctness

   If the TTL attribute is missing or not a Number with epoch seconds, TTL won't delete items.

2. Step 2: Verify other options

   TTL works regardless of region, does not require manual activation, and does not need to be primary key.

3. Final Answer:

   TTL attribute expiry is missing or has wrong data type -> Option B

4. Quick Check:

   Wrong TTL attribute = no deletion [OK]

Hint: TTL attribute must exist and be correct type [OK]

Common Mistakes:

• Thinking TTL depends on table region
• Believing TTL needs manual daily activation
• Assuming TTL attribute must be primary key

5. You want to store session data that expires exactly 30 minutes after creation using DynamoDB TTL. Which approach correctly sets the TTL attribute?

hard

A. Set TTL attribute to current Unix epoch time in seconds plus 1800 seconds

B. Set TTL attribute to current time as ISO string plus 30 minutes

C. Set TTL attribute to Boolean true when session expires

D. Set TTL attribute to current Unix epoch time in milliseconds plus 1800000

Solution

1. Step 1: Calculate TTL value correctly

   TTL attribute must be a Number in seconds, so add 1800 seconds (30 minutes) to current epoch seconds.

2. Step 2: Eliminate incorrect formats

   ISO strings, Booleans, or milliseconds are invalid for TTL attribute in DynamoDB.

3. Final Answer:

   Set TTL attribute to current Unix epoch time in seconds plus 1800 seconds -> Option A

4. Quick Check:

   TTL = epoch seconds + 1800 [OK]

Hint: TTL value = current epoch seconds + 1800 for 30 minutes [OK]

Common Mistakes:

• Using ISO date strings instead of epoch seconds
• Using milliseconds instead of seconds
• Setting TTL as Boolean instead of number