Question 470 of 302
SAA-C03 Design High-Performing Architectures Practice Question
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.
⚠ Common exam trap
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.
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.
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.
- ✓
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.
- ✗
Put the service behind API Gateway REST API and use Lambda integration.
Why it's wrong here
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.
- ✗
Use CloudFront to cache the binary packets at edge locations.
Why it's wrong here
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.
- ✗
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.
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Last reviewed: Jun 11, 2026
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