Table capacity modes (on-demand vs provisioned) in DynamoDB - Hands-On Comparison

DynamoDB Table Capacity Modes: On-Demand vs Provisioned

📖 Scenario: You are building a simple inventory system for a small online store. You want to create a DynamoDB table to store product information. You need to decide how to set the table's capacity mode to handle read and write traffic efficiently.

🎯 Goal: Create a DynamoDB table named Products with a primary key ProductID. First, set up the table with the Provisioned capacity mode and specify read and write capacity units. Then, change the capacity mode to On-Demand to allow automatic scaling without specifying capacity units.

📋 What You'll Learn

Create a DynamoDB table named Products with ProductID as the partition key.

Set the table's capacity mode to Provisioned with ReadCapacityUnits set to 5 and WriteCapacityUnits set to 5.

Add a configuration variable to switch the capacity mode to On-Demand.

Update the table creation code to use the On-Demand capacity mode when the configuration variable is set.

💡 Why This Matters

🌍 Real World

Choosing the right capacity mode in DynamoDB helps manage costs and performance for applications with varying traffic patterns.

💼 Career

Understanding DynamoDB capacity modes is essential for cloud developers and database administrators working with AWS to optimize database scalability and cost.

1

Create DynamoDB table with Provisioned capacity mode

Write the AWS CLI command to create a DynamoDB table named Products with ProductID as the partition key. Set the capacity mode to Provisioned with ReadCapacityUnits and WriteCapacityUnits both set to 5.

DynamoDB

# Your AWS CLI command here to create the table with provisioned capacity

Hint

Use aws dynamodb create-table with --provisioned-throughput to set capacity units.

2

Add configuration variable for capacity mode

Create a shell variable named CAPACITY_MODE and set it to PROVISIONED to represent the current capacity mode setting.

DynamoDB

aws dynamodb create-table \
    --table-name Products \
    --attribute-definitions AttributeName=ProductID,AttributeType=S \
    --key-schema AttributeName=ProductID,KeyType=HASH \
    --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

# Define capacity mode variable
# Your code here

Hint

Use CAPACITY_MODE=PROVISIONED to set the variable.

3

Write conditional logic to choose capacity mode

Write a shell if statement that checks if CAPACITY_MODE equals PROVISIONED. If yes, set a variable CAPACITY_PARAMS to --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5. Otherwise, set CAPACITY_PARAMS to --billing-mode PAY_PER_REQUEST for on-demand mode.

DynamoDB

aws dynamodb create-table \
    --table-name Products \
    --attribute-definitions AttributeName=ProductID,AttributeType=S \
    --key-schema AttributeName=ProductID,KeyType=HASH \
    --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

CAPACITY_MODE=PROVISIONED

# Add if statement to set CAPACITY_PARAMS based on CAPACITY_MODE
# Your code here

Hint

Use if [ "$CAPACITY_MODE" = "PROVISIONED" ] to check the variable.

4

Create table using dynamic capacity mode parameter

Rewrite the AWS CLI command to create the Products table using the variable CAPACITY_PARAMS for capacity settings instead of hardcoding. This will allow switching between provisioned and on-demand modes by changing CAPACITY_MODE.

DynamoDB

aws dynamodb create-table \
    --table-name Products \
    --attribute-definitions AttributeName=ProductID,AttributeType=S \
    --key-schema AttributeName=ProductID,KeyType=HASH \
    $CAPACITY_PARAMS

CAPACITY_MODE=PROVISIONED

if [ "$CAPACITY_MODE" = "PROVISIONED" ]; then
    CAPACITY_PARAMS="--provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5"
else
    CAPACITY_PARAMS="--billing-mode PAY_PER_REQUEST"
fi

# Use $CAPACITY_PARAMS in the create-table command
# Your code here

Hint

Use $CAPACITY_PARAMS in the create-table command to apply the selected capacity mode.

Practice

1. Which DynamoDB table capacity mode automatically adjusts to your application's traffic without requiring manual capacity settings?

easy

A. On-demand mode

B. Provisioned mode

C. Reserved mode

D. Manual mode

Solution

1. Step 1: Understand capacity modes in DynamoDB

   DynamoDB offers two main capacity modes: on-demand and provisioned. On-demand mode automatically adjusts capacity based on traffic.

2. Step 2: Identify the mode that adjusts automatically

   On-demand mode charges per request and scales automatically without manual settings, unlike provisioned mode which requires fixed capacity.

3. Final Answer:

   On-demand mode -> Option A

4. Quick Check:

   Automatic scaling = On-demand mode [OK]

Hint: Automatic scaling means on-demand mode [OK]

Common Mistakes:

• Confusing provisioned mode as automatic
• Thinking reserved or manual modes exist
• Assuming manual capacity adjustment is automatic

2. Which of the following is the correct way to specify provisioned capacity when creating a DynamoDB table using AWS CLI?

easy

A. --billing-mode PAY_PER_REQUEST

B. --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5

C. --capacity-mode ON_DEMAND

D. --read-write-capacity 10

Solution

1. Step 1: Recall AWS CLI syntax for provisioned capacity

   Provisioned mode requires specifying read and write capacity units using --provisioned-throughput with ReadCapacityUnits and WriteCapacityUnits.

2. Step 2: Match correct syntax option

   --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 uses the correct syntax. The --billing-mode PAY_PER_REQUEST and --capacity-mode ON_DEMAND options specify on-demand mode, while --read-write-capacity is invalid.

3. Final Answer:

   --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 -> Option B

4. Quick Check:

   Provisioned throughput syntax = --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 [OK]

Hint: Provisioned mode uses --provisioned-throughput flag [OK]

Common Mistakes:

• Using PAY_PER_REQUEST flag for provisioned mode
• Confusing capacity mode flags
• Using invalid flags like --read-write-capacity

3. Consider a DynamoDB table in provisioned mode with ReadCapacityUnits=5 and WriteCapacityUnits=5. If your application suddenly sends 20 read requests per second, what will happen?

medium

A. All 20 read requests succeed without delay

B. The table switches to on-demand mode automatically

C. Some read requests may be throttled due to exceeding capacity

D. DynamoDB automatically increases capacity to handle 20 requests

Solution

1. Step 1: Understand provisioned capacity limits

   Provisioned mode sets fixed read/write capacity units. Here, 5 read units allow about 5 strongly consistent reads per second.

2. Step 2: Analyze traffic exceeding capacity

   Sending 20 read requests exceeds the provisioned 5 units. DynamoDB throttles excess requests instead of automatically scaling or switching modes.

3. Final Answer:

   Some read requests may be throttled due to exceeding capacity -> Option C

4. Quick Check:

   Exceeding provisioned units causes throttling [OK]

Hint: Provisioned mode throttles if requests exceed capacity [OK]

Common Mistakes:

• Assuming automatic scaling in provisioned mode
• Thinking all requests always succeed
• Believing table switches modes automatically

4. You created a DynamoDB table with the following command:

aws dynamodb create-table --table-name MyTable --billing-mode PROVISIONED

But you forgot to specify provisioned throughput. What will happen?

medium

A. Table is created with default capacity of 5 read and 5 write units

B. Table is created but capacity is unlimited

C. Table is created in on-demand mode automatically

D. Table creation fails with an error about missing provisioned throughput

Solution

1. Step 1: Check requirements for provisioned mode

   Provisioned mode requires specifying ReadCapacityUnits and WriteCapacityUnits explicitly during table creation.

2. Step 2: Understand AWS CLI behavior on missing parameters

   Omitting provisioned throughput causes AWS CLI to return an error because required parameters are missing.

3. Final Answer:

   Table creation fails with an error about missing provisioned throughput -> Option D

4. Quick Check:

   Missing provisioned throughput causes creation error [OK]

Hint: Provisioned mode needs capacity units specified [OK]

Common Mistakes:

• Assuming default capacity is assigned
• Thinking table switches to on-demand mode
• Believing capacity is unlimited without settings

5. A startup expects unpredictable traffic spikes but wants to control costs during low usage. Which DynamoDB capacity mode strategy is best to balance cost and performance?

hard

A. Use on-demand mode to automatically handle spikes and pay per request

B. Use provisioned mode with low capacity and manually increase during spikes

C. Use provisioned mode with high capacity to handle spikes

D. Switch between on-demand and provisioned modes daily

Solution

1. Step 1: Analyze startup traffic pattern

   Unpredictable spikes mean traffic varies a lot, so automatic scaling is important to avoid throttling or overpaying.

2. Step 2: Evaluate capacity mode options for cost and performance

   On-demand mode charges per request and scales automatically, ideal for unpredictable traffic and cost control. Provisioned mode requires manual adjustments and risks throttling or wasted capacity.

3. Final Answer:

   Use on-demand mode to automatically handle spikes and pay per request -> Option A

4. Quick Check:

   Unpredictable traffic = On-demand mode best [OK]

Hint: Unpredictable traffic? Choose on-demand mode [OK]

Common Mistakes:

• Choosing high provisioned capacity wastes money
• Manually adjusting capacity is slow and error-prone
• Switching modes daily is not supported