- A
Keep the Application Load Balancer (ALB), because ALBs also preserve client source IP for TCP protocols.
Why wrong: ALBs are optimized for Layer 7 (HTTP/HTTPS) routing semantics. For a custom binary TCP protocol, ALB behavior and feature set do not align as well with pure Layer 4 TCP health checking and consistently low-latency forwarding. Using ALB for generic TCP services is commonly a poor fit compared to an NLB.
- B
Use a Network Load Balancer (NLB) with TCP listeners so traffic stays at Layer 4 and the original source IP is preserved.
NLB is designed for Layer 4 TCP/UDP traffic with very low latency and high throughput. It supports TCP health checks and preserves the original client source IP by default, which enables accurate client-IP-based rate limiting for a custom TCP protocol.
- C
Use Amazon API Gateway because it preserves client source IP and provides TCP health checks for all protocols.
Why wrong: API Gateway is intended for HTTP APIs, REST APIs, and WebSockets. It is not designed to proxy arbitrary custom TCP binary protocols with Layer 4 TCP health checks, so it does not satisfy the core protocol/health-check and latency requirements.
- D
Use Amazon CloudFront with an S3 origin, because CloudFront reduces latency for TCP-based protocols.
Why wrong: CloudFront is primarily an HTTP(S) distribution service and does not function as a Layer 4 TCP load balancer for a custom TCP binary protocol with TCP health checks. S3 origins are also not an appropriate backend for a live TCP service response path.
Quick Answer
The answer is to use a Network Load Balancer (NLB) with TCP listeners because it operates at Layer 4, preserving the original client source IP by default for accurate rate limiting while delivering the low-latency, high-throughput performance required for custom binary protocols. Unlike an Application Load Balancer, which terminates TCP connections and rewrites the source IP at Layer 7, an NLB forwards packets without modification, keeping latency minimal and supporting native TCP health checks. On the SAA-C03 exam, this scenario tests your understanding of when to choose Layer 4 versus Layer 7 load balancing—a common trap is assuming an ALB can handle all TCP workloads, but its proxy behavior adds overhead and breaks source IP preservation. Remember the memory tip: “NLB for native IP, ALB for app-aware.”
SAA-C03 Design High-Performing Architectures Practice Question
This SAA-C03 practice question tests your understanding of design high-performing 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.
Your company needs a high-throughput, low-latency TCP service using a custom binary protocol. Requirements: preserve the original client source IP for rate limiting, keep latency minimal, and use TCP health checks. The current setup uses an Application Load Balancer and performance is inconsistent. Which load balancer choice best meets these requirements?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"best"Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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
Use a Network Load Balancer (NLB) with TCP listeners so traffic stays at Layer 4 and the original source IP is preserved.
A Network Load Balancer (NLB) operates at Layer 4 and preserves the original client source IP by default, which is essential for accurate rate limiting. Its TCP listeners provide low-latency, high-throughput handling of custom binary protocols, and it supports TCP health checks natively. This directly addresses the performance inconsistency seen with the Application Load Balancer, which operates at Layer 7 and introduces additional processing overhead.
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.
- ✗
Keep the Application Load Balancer (ALB), because ALBs also preserve client source IP for TCP protocols.
Why it's wrong here
ALBs are optimized for Layer 7 (HTTP/HTTPS) routing semantics. For a custom binary TCP protocol, ALB behavior and feature set do not align as well with pure Layer 4 TCP health checking and consistently low-latency forwarding. Using ALB for generic TCP services is commonly a poor fit compared to an NLB.
- ✓
Use a Network Load Balancer (NLB) with TCP listeners so traffic stays at Layer 4 and the original source IP is preserved.
Why this is correct
NLB is designed for Layer 4 TCP/UDP traffic with very low latency and high throughput. It supports TCP health checks and preserves the original client source IP by default, which enables accurate client-IP-based rate limiting for a custom TCP protocol.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use Amazon API Gateway because it preserves client source IP and provides TCP health checks for all protocols.
- ✗
Use Amazon CloudFront with an S3 origin, because CloudFront reduces latency for TCP-based protocols.
Why it's wrong here
CloudFront is primarily an HTTP(S) distribution service and does not function as a Layer 4 TCP load balancer for a custom TCP binary protocol with TCP health checks. S3 origins are also not an appropriate backend for a live TCP service response path.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume Application Load Balancers preserve client source IP for all protocols, but they only do so for HTTP/HTTPS traffic via the X-Forwarded-For header, not for raw TCP traffic, and they introduce higher latency due to Layer 7 processing.
Detailed technical explanation
How to think about this question
Under the hood, an NLB uses a flow hash algorithm to route packets without inspecting the payload, which keeps latency minimal and allows it to handle millions of requests per second. The preservation of client source IP is achieved because the NLB does not terminate the TCP connection; instead, it forwards packets directly to the target, so the backend sees the original client IP. In a real-world scenario, if your rate-limiting logic relies on the client IP, using an ALB would cause all traffic to appear from the ALB's IP, breaking the rate limiter and potentially allowing a single client to overwhelm the backend.
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
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FAQ
Questions learners often ask
What does this SAA-C03 question test?
Design High-Performing Architectures — This question tests Design High-Performing Architectures — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use a Network Load Balancer (NLB) with TCP listeners so traffic stays at Layer 4 and the original source IP is preserved. — A Network Load Balancer (NLB) operates at Layer 4 and preserves the original client source IP by default, which is essential for accurate rate limiting. Its TCP listeners provide low-latency, high-throughput handling of custom binary protocols, and it supports TCP health checks natively. This directly addresses the performance inconsistency seen with the Application Load Balancer, which operates at Layer 7 and introduces additional processing overhead.
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: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
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
This SAA-C03 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 SAA-C03 exam.
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