DynamoDB capacity modes (on-demand, provisioned) in AWS - Mini Project: Build & Apply

DynamoDB Capacity Modes Setup

📖 Scenario: You are setting up a DynamoDB table for a new application. You need to create the table with initial data and then configure its capacity mode to handle traffic efficiently.

🎯 Goal: Build a DynamoDB table configuration with initial attributes and set its capacity mode to either on-demand or provisioned.

📋 What You'll Learn

Create a DynamoDB table named Users with a primary key UserId of type string.

Add a configuration variable capacity_mode to select between PAY_PER_REQUEST (on-demand) and PROVISIONED modes.

If capacity_mode is PROVISIONED, configure ReadCapacityUnits and WriteCapacityUnits with exact values.

Complete the table creation configuration including the capacity mode settings.

💡 Why This Matters

🌍 Real World

DynamoDB capacity modes help manage costs and performance for applications with varying traffic patterns.

💼 Career

Understanding how to configure DynamoDB tables with correct capacity modes is essential for cloud engineers and developers working with AWS.

1

Create DynamoDB table data structure

Create a dictionary called table_definition with the following keys and values exactly: TableName set to 'Users', KeySchema as a list with one dictionary having AttributeName as 'UserId' and KeyType as 'HASH', and AttributeDefinitions as a list with one dictionary having AttributeName as 'UserId' and AttributeType as 'S'.

AWS

# Create the DynamoDB table definition dictionary
# Your code here

Hint

Use a dictionary with keys TableName, KeySchema, and AttributeDefinitions exactly as described.

2

Add capacity mode configuration variable

Add a variable called capacity_mode and set it to the string 'PAY_PER_REQUEST' to represent on-demand capacity mode.

AWS

table_definition = {
    'TableName': 'Users',
    'KeySchema': [
        {'AttributeName': 'UserId', 'KeyType': 'HASH'}
    ],
    'AttributeDefinitions': [
        {'AttributeName': 'UserId', 'AttributeType': 'S'}
    ]
}
# Define the capacity_mode variable
# Your code here

Hint

Set capacity_mode exactly to 'PAY_PER_REQUEST' to select on-demand mode.

3

Add provisioned capacity settings conditionally

Add a conditional block that checks if capacity_mode equals 'PROVISIONED'. Inside this block, add a key ProvisionedThroughput to table_definition with a dictionary value containing ReadCapacityUnits set to 5 and WriteCapacityUnits set to 5.

AWS

table_definition = {
    'TableName': 'Users',
    'KeySchema': [
        {'AttributeName': 'UserId', 'KeyType': 'HASH'}
    ],
    'AttributeDefinitions': [
        {'AttributeName': 'UserId', 'AttributeType': 'S'}
    ]
}
capacity_mode = 'PAY_PER_REQUEST'
# Add provisioned throughput settings if capacity_mode is 'PROVISIONED'
# Your code here

Hint

Use an if statement to add ProvisionedThroughput only when capacity_mode is 'PROVISIONED'.

4

Complete table creation configuration with capacity mode

Add a key BillingMode to table_definition and set its value to the current capacity_mode variable.

AWS

table_definition = {
    'TableName': 'Users',
    'KeySchema': [
        {'AttributeName': 'UserId', 'KeyType': 'HASH'}
    ],
    'AttributeDefinitions': [
        {'AttributeName': 'UserId', 'AttributeType': 'S'}
    ]
}
capacity_mode = 'PAY_PER_REQUEST'
if capacity_mode == 'PROVISIONED':
    table_definition['ProvisionedThroughput'] = {
        'ReadCapacityUnits': 5,
        'WriteCapacityUnits': 5
    }
# Set the BillingMode key in table_definition to capacity_mode
# Your code here

Hint

Assign capacity_mode to the BillingMode key in table_definition.

Practice

1. What is the main advantage of using DynamoDB's on-demand capacity mode?

easy

A. It offers a lower cost for steady, predictable workloads.

B. It automatically scales to handle any workload without manual capacity planning.

C. It requires you to set fixed read and write capacity units.

D. It limits the number of requests per second to a fixed amount.

Solution

1. Step 1: Understand on-demand mode behavior

   On-demand mode automatically adjusts capacity to meet traffic demands without manual input.

2. Step 2: Compare with provisioned mode

   Provisioned mode requires fixed capacity settings, unlike on-demand.

3. Final Answer:

   It automatically scales to handle any workload without manual capacity planning. -> Option B

4. Quick Check:

   On-demand = auto scaling without setup [OK]

Hint: On-demand means auto scale, no manual setup needed [OK]

Common Mistakes:

• Confusing on-demand with provisioned fixed capacity
• Thinking on-demand limits requests
• Assuming on-demand is cheaper for steady workloads

2. Which of the following is the correct way to specify provisioned capacity in a DynamoDB table creation JSON?

easy

A. { "Throughput": { "Reads": 5, "Writes": 10 } }

B. { "CapacityMode": "ON_DEMAND" }

C. { "ProvisionedThroughput": { "ReadCapacityUnits": 5, "WriteCapacityUnits": 10 } }

D. { "ReadUnits": 5, "WriteUnits": 10 }

Solution

1. Step 1: Recall provisioned capacity syntax

   Provisioned mode requires specifying ReadCapacityUnits and WriteCapacityUnits inside ProvisionedThroughput.

2. Step 2: Check options for correct JSON structure

   { "ProvisionedThroughput": { "ReadCapacityUnits": 5, "WriteCapacityUnits": 10 } } matches the correct AWS DynamoDB API format for provisioned throughput.

3. Final Answer:

   { "ProvisionedThroughput": { "ReadCapacityUnits": 5, "WriteCapacityUnits": 10 } } -> Option C

4. Quick Check:

   ProvisionedThroughput with Read/Write units = correct syntax [OK]

Hint: Provisioned capacity uses ProvisionedThroughput with Read/Write units [OK]

Common Mistakes:

• Using CapacityMode for provisioned capacity
• Missing ProvisionedThroughput wrapper
• Incorrect property names like ReadUnits

3. Given a DynamoDB table in provisioned mode with 5 read capacity units and 5 write capacity units, what happens if your application suddenly sends 20 write requests per second?

medium

A. Some write requests are throttled because they exceed the provisioned write capacity.

B. All 20 write requests succeed immediately without throttling.

C. DynamoDB automatically increases write capacity to 20 units instantly.

D. The table switches automatically to on-demand mode to handle the load.

Solution

1. Step 1: Understand provisioned capacity limits

   Provisioned mode limits throughput to the set capacity units (5 writes per second here).

2. Step 2: Analyze effect of exceeding capacity

   Sending 20 writes exceeds 5 units, causing throttling of excess requests.

3. Final Answer:

   Some write requests are throttled because they exceed the provisioned write capacity. -> Option A

4. Quick Check:

   Provisioned mode throttles excess requests [OK]

Hint: Provisioned mode throttles requests above set capacity [OK]

Common Mistakes:

• Assuming automatic capacity increase in provisioned mode
• Thinking on-demand mode applies automatically
• Believing all requests always succeed

4. You configured a DynamoDB table with provisioned capacity: 10 read units and 10 write units. Your application experiences throttling errors during peak hours. What is the best immediate fix to reduce throttling without downtime?

medium

A. Switch the table to on-demand capacity mode.

B. Reduce the size of items stored in the table.

C. Delete and recreate the table with higher capacity.

D. Increase the provisioned read and write capacity units.

Solution

1. Step 1: Identify cause of throttling

   Throttling occurs because provisioned capacity is too low for peak traffic.

2. Step 2: Choose immediate fix without downtime

   Increasing provisioned capacity units can be done live without deleting the table.

3. Final Answer:

   Increase the provisioned read and write capacity units. -> Option D

4. Quick Check:

   Increase capacity units to reduce throttling [OK]

Hint: Increase provisioned units live to fix throttling fast [OK]

Common Mistakes:

• Deleting and recreating table causes downtime
• Assuming switching to on-demand is instant and free
• Reducing item size does not fix capacity limits

5. A startup expects unpredictable traffic spikes and wants to minimize cost during low usage while avoiding throttling during spikes. Which DynamoDB capacity mode should they choose and why?

hard

A. On-demand mode because it charges per request and scales instantly without manual setup.

B. Provisioned mode with auto scaling enabled to adjust capacity automatically.

C. Provisioned mode with fixed capacity to control costs strictly.

D. On-demand mode but with a fixed maximum request limit to save costs.

Solution

1. Step 1: Understand startup's needs

   They want to avoid throttling during spikes and save cost during low usage.

2. Step 2: Compare capacity modes for unpredictable traffic

   On-demand mode charges per request and auto scales instantly, ideal for unpredictable spikes.

3. Step 3: Evaluate other options

   Provisioned with auto scaling helps but requires setup and may lag; fixed capacity risks throttling or cost waste.

4. Final Answer:

   On-demand mode because it charges per request and scales instantly without manual setup. -> Option A

5. Quick Check:

   Unpredictable traffic = on-demand mode best [OK]

Hint: Unpredictable spikes? Choose on-demand for auto scaling [OK]

Common Mistakes:

• Choosing fixed provisioned capacity for unpredictable traffic
• Assuming auto scaling is instant and always perfect
• Thinking on-demand has fixed request limits