- A
Replace the Application Load Balancer with a Network Load Balancer.
A Network Load Balancer is the right choice for TCP traffic and low-latency forwarding at layer 4. It also supports static IP behavior that is important for partner allowlisting. This directly matches the custom binary protocol and source-IP requirement.
- B
Use a TCP listener on the load balancer instead of an HTTP or HTTPS listener.
A TCP listener avoids HTTP parsing and preserves the protocol as raw TCP, which is required for a custom binary service. It keeps the load balancer aligned with the application protocol rather than forcing a web-oriented layer 7 design. That is the correct protocol-level fit here.
- C
Put the service behind API Gateway REST API and use Lambda integration.
Why wrong: API Gateway is designed for API requests, not arbitrary custom binary TCP sessions. It would not preserve the required protocol semantics or satisfy the static allowlisting requirement for this use case. It is the wrong abstraction for raw TCP traffic.
- D
Use CloudFront to cache the binary packets at edge locations.
Why wrong: CloudFront is optimized for HTTP and HTTPS content delivery and caching, not for arbitrary TCP application protocols. It does not solve static IP allowlisting or source-IP preservation for a custom binary service. Caching is irrelevant to the described workload.
- E
Terminate the traffic with an Amazon RDS proxy to stabilize the connections.
Why wrong: RDS Proxy is for database connection management, not for fronting a TCP application service. It has no role in preserving source IP for a custom binary protocol or in providing allowlisted endpoint addresses. This is a mismatch to the workload.
Quick Answer
The answer is a Network Load Balancer with a TCP listener and static IPs via Elastic IPs. This is correct because the NLB operates at Layer 4, handling raw TCP traffic natively without inspecting the payload, which is essential for a custom binary TCP protocol that an Application Load Balancer cannot parse. Additionally, the NLB preserves the original client source IP by default when targets are in private subnets, enabling accurate rate limiting based on the client’s IP address. On the SAA-C03 exam, this scenario tests your understanding of when to choose an NLB over an ALB—specifically for non-HTTP/HTTPS protocols and for source IP preservation. A common trap is selecting an ALB with a TCP listener, but ALBs only support HTTP/HTTPS at Layer 7. Remember the mnemonic: “NLB for TCP, ALB for HTTP; source IP stays with NLB.”
SAA-C03 Design High-Performing Architectures Practice Question
This SAA-C03 practice question tests your understanding of design high-performing architectures. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 partner integration sends a custom binary TCP protocol to a service running on EC2 instances in private subnets. The partners require static endpoint IPs for allowlisting, and the application must see the original client source IP for rate limiting. Which two changes best fit the protocol and network requirements? Select two.
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
Replace the Application Load Balancer with a Network Load Balancer.
A Network Load Balancer (NLB) is required because it supports TCP traffic natively at Layer 4, which is necessary for a custom binary TCP protocol that cannot be interpreted by an Application Load Balancer (ALB) at Layer 7. Additionally, an NLB preserves the original client source IP address by default when used with targets in private subnets, meeting the requirement for rate limiting based on the client IP. Static IP addresses can be assigned to the NLB via Elastic IPs, satisfying the partner's need for static endpoint IPs for allowlisting.
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.
- ✓
Replace the Application Load Balancer with a Network Load Balancer.
Why this is correct
A Network Load Balancer is the right choice for TCP traffic and low-latency forwarding at layer 4. It also supports static IP behavior that is important for partner allowlisting. This directly matches the custom binary protocol and source-IP requirement.
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 a TCP listener on the load balancer instead of an HTTP or HTTPS listener.
Why this is correct
A TCP listener avoids HTTP parsing and preserves the protocol as raw TCP, which is required for a custom binary service. It keeps the load balancer aligned with the application protocol rather than forcing a web-oriented layer 7 design. That is the correct protocol-level fit here.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Put the service behind API Gateway REST API and use Lambda integration.
- ✗
Use CloudFront to cache the binary packets at edge locations.
- ✗
Terminate the traffic with an Amazon RDS proxy to stabilize the connections.
Why it's wrong here
RDS Proxy is for database connection management, not for fronting a TCP application service. It has no role in preserving source IP for a custom binary protocol or in providing allowlisted endpoint addresses. This is a mismatch to the workload.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume an Application Load Balancer can handle any TCP traffic because it supports TCP listeners, but ALB only supports HTTP/HTTPS at Layer 7 and cannot process custom binary protocols, while NLB is the correct choice for non-HTTP TCP traffic with static IP and client IP preservation requirements.
Detailed technical explanation
How to think about this question
NLB operates at Layer 4 of the OSI model, forwarding TCP/UDP traffic without inspecting payload content, which is ideal for binary protocols. When targets are in private subnets, NLB uses the 'preserve client IP' feature by default, which means the source IP in the packet header remains the original client IP, not the NLB's IP. This is critical for rate-limiting logic that relies on client IP addresses, as opposed to ALB which replaces the source IP with its own. Static IP assignment via Elastic IPs ensures partners can reliably allowlist the NLB endpoints, as NLB supports one Elastic IP per Availability Zone.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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 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: Replace the Application Load Balancer with a Network Load Balancer. — A Network Load Balancer (NLB) is required because it supports TCP traffic natively at Layer 4, which is necessary for a custom binary TCP protocol that cannot be interpreted by an Application Load Balancer (ALB) at Layer 7. Additionally, an NLB preserves the original client source IP address by default when used with targets in private subnets, meeting the requirement for rate limiting based on the client IP. Static IP addresses can be assigned to the NLB via Elastic IPs, satisfying the partner's need for static endpoint IPs for allowlisting.
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
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