DVA-C02 Development with AWS Services Practice Question
A developer is using Amazon DynamoDB to store session data for a web application. The application reads and writes a single item per user session. The traffic pattern shows occasional spikes. The developer wants to minimize read and write costs. Which DynamoDB capacity mode should the developer choose?
⚠ Common exam trap
A common mix-up: candidates confuse 'Reserved capacity' with a valid DynamoDB option or assume that auto scaling (Option D) is always the cheapest for variable traffic, but on-demand is specifically designed for unpredictable spikes to avoid over-provisioning costs and throttling.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
On-demand capacity
On-demand capacity mode is ideal for unpredictable traffic patterns with occasional spikes because it automatically scales read and write throughput based on actual usage, charging only for consumed operations. Since the application reads and writes a single item per session and experiences spikes, on-demand eliminates the need to provision for peak capacity, minimizing costs compared to over-provisioning.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Reserved capacity
Why it's wrong here
Reserved capacity for DynamoDB is a pricing model, not a capacity mode, allowing users to commit to a certain level of provisioned throughput (read and write capacity units) for a 1-year or 3-year term in exchange for significant cost savings. However, this model requires a consistent and predictable baseline workload to be cost-effective. Session data, by its nature, often experiences highly variable and unpredictable traffic patterns, making a fixed, upfront commitment unsuitable and potentially leading to either over-provisioning or throttling during peak times.
- ✓
On-demand capacity
Why this is correct
DynamoDB On-demand capacity mode is specifically designed for workloads with unpredictable traffic patterns and sudden, sharp spikes. It operates on a pay-per-request model, automatically scaling throughput up or down instantly to accommodate actual traffic volume without requiring any capacity planning. This eliminates the risk of throttling during peak loads and avoids over-provisioning during quiet periods, making it ideal for highly variable session data.
- ✗
Provisioned capacity with manual scaling
Why it's wrong here
Provisioned capacity with manual scaling requires a developer to explicitly define the desired read and write capacity units (RCUs/WCUs) for a table. To handle traffic spikes, a human operator would need to manually increase these settings. This approach is inherently slow and reactive, making it impossible to respond in real-time to sudden, unpredictable bursts of session data traffic, inevitably leading to throttling and poor user experience during peak demand.
- ✗
Provisioned capacity with auto scaling
Why it's wrong here
DynamoDB auto scaling for provisioned capacity dynamically adjusts RCUs and WCUs based on actual usage and predefined target utilization. While it automates scaling, there are inherent delays due to CloudWatch metric aggregation and cool-down periods between scaling events. For extremely sharp, sudden spikes in session data, auto scaling might not react quickly enough to prevent initial throttling before the new capacity is fully provisioned and available.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This DVA-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DVA-C02 exam.