- A
Switch from REST APIs to HTTP APIs if the feature set is sufficient.
HTTP APIs are generally lower cost and lower latency than REST APIs for many simple API use cases. They reduce the recurring API Gateway cost without requiring a redesign.
- B
Schedule Lambda provisioned concurrency shortly before the spike and scale it back afterward.
Scheduled provisioned concurrency targets the predictable burst window instead of paying for warm capacity all day. It balances latency improvement with controlled spend.
- C
Keep provisioned concurrency at the maximum level 24/7.
Why wrong: Always-on provisioned concurrency removes cold starts, but it also creates continuous cost even when traffic is low. That directly conflicts with the goal of avoiding unnecessary spend.
- D
Move the API to a single t3.nano EC2 instance.
Why wrong: A single tiny instance creates an availability and scaling bottleneck, and it shifts operational burden back to the team. It is not a cost-optimized or resilient replacement for serverless.
- E
Add an S3 gateway endpoint to reduce cold starts.
Why wrong: S3 gateway endpoints help with private S3 access and NAT avoidance, not Lambda cold starts. This option addresses a different problem entirely.
Quick Answer
The answer is to schedule Lambda provisioned concurrency to activate shortly before the 09:00 UTC spike and then scale it back afterward, combined with migrating from API Gateway REST APIs to HTTP APIs. Provisioned concurrency pre-warms a set number of Lambda execution environments, eliminating cold starts during the predictable traffic surge, while scheduling it only for the spike window avoids paying for all-day provisioned concurrency. HTTP APIs further reduce latency and cost per request compared to REST APIs, directly addressing the team’s goal of minimizing both cold start impact and unnecessary spending. On the SAA-C03 exam, this tests your understanding of Lambda scaling and API Gateway optimization—a common trap is choosing always-on provisioned concurrency or ignoring the HTTP API upgrade, which wastes cost. Memory tip: think “warm the pool, then drain it” for provisioned concurrency, and “HTTP is faster and cheaper” for the API swap.
SAA-C03 Design Cost-Optimized Architectures Practice Question
This SAA-C03 practice question tests your understanding of design cost-optimized architectures. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A public API currently uses API Gateway REST APIs and Lambda. Traffic is low most of the day, but marketing runs a predictable traffic spike every weekday at 09:00 UTC. Users complain about cold starts during the first few minutes of the spike, and the team wants to avoid paying for provisioned concurrency all day. Which two changes should they make? Select two.
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"first"Why it matters: Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
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
Switch from REST APIs to HTTP APIs if the feature set is sufficient.
Option A is correct because HTTP APIs are designed to be faster and more cost-effective than REST APIs, with up to 71% lower latency and 60% lower cost per request. This reduces the impact of cold starts by minimizing the overhead of request processing, and the cost savings align with the team's goal of avoiding all-day provisioned concurrency costs.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Switch from REST APIs to HTTP APIs if the feature set is sufficient.
Why this is correct
HTTP APIs are generally lower cost and lower latency than REST APIs for many simple API use cases. They reduce the recurring API Gateway cost without requiring a redesign.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Schedule Lambda provisioned concurrency shortly before the spike and scale it back afterward.
Why this is correct
Scheduled provisioned concurrency targets the predictable burst window instead of paying for warm capacity all day. It balances latency improvement with controlled spend.
Clue confirmation
The clue word "first" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Keep provisioned concurrency at the maximum level 24/7.
Why it's wrong here
Always-on provisioned concurrency removes cold starts, but it also creates continuous cost even when traffic is low. That directly conflicts with the goal of avoiding unnecessary spend.
- ✗
Move the API to a single t3.nano EC2 instance.
Why it's wrong here
A single tiny instance creates an availability and scaling bottleneck, and it shifts operational burden back to the team. It is not a cost-optimized or resilient replacement for serverless.
- ✗
Add an S3 gateway endpoint to reduce cold starts.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think provisioned concurrency must be always-on to be effective, or that adding infrastructure like EC2 or S3 endpoints can solve cold starts, when in fact the correct approach is to combine a cheaper API type with time-based provisioned concurrency scheduling.
Detailed technical explanation
How to think about this question
Lambda cold starts occur when a new execution environment is initialized, which includes downloading the code, starting the runtime, and running initialization code outside the handler. Provisioned concurrency keeps a number of environments warm and ready, but it incurs costs even when idle; scheduling it with EventBridge or a cron job allows you to activate it only during the spike window, then deactivate it to save costs. HTTP APIs use a simpler, connection-oriented protocol (WebSocket and HTTP/2) compared to REST APIs, which reduces per-request overhead and improves response times.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design Cost-Optimized Architectures — This question tests Design Cost-Optimized Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Switch from REST APIs to HTTP APIs if the feature set is sufficient. — Option A is correct because HTTP APIs are designed to be faster and more cost-effective than REST APIs, with up to 71% lower latency and 60% lower cost per request. This reduces the impact of cold starts by minimizing the overhead of request processing, and the cost savings align with the team's goal of avoiding all-day provisioned concurrency costs.
What should I do if I get this SAA-C03 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "first". Order matters here. You are being tested on which action comes before the others — not which action is generally useful.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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