The correct choice is a Network Load Balancer (NLB) with an Elastic IP address because it directly provides a fixed IP address for whitelisting highly available across AZs. An NLB operates at Layer 4, allowing you to assign a static Elastic IP per Availability Zone, which gives external partners a stable, unchanging IP to whitelist while the load balancer automatically distributes traffic across healthy targets in multiple zones. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how to meet strict IP-based security requirements without sacrificing resilience—a common trap is choosing an Application Load Balancer, which lacks static IP support and uses a dynamic DNS name instead. Remember the memory tip: “NLB for IPs that stay fixed, ALB for DNS that gets mixed.”
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. 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 company is migrating a legacy on-premises application to AWS. The application requires a fixed IP address for whitelisting by external partners. The solution must be highly available across multiple Availability Zones. Which design should they use?
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 an Elastic IP address.
Option C is correct because a Network Load Balancer (NLB) supports static IP addresses via Elastic IPs per Availability Zone, providing a fixed IP for partner whitelisting while maintaining high availability across multiple AZs. Unlike ALBs, NLBs operate at Layer 4 and can preserve the client IP, which is critical for IP-based whitelisting scenarios.
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.
✗
Use an Application Load Balancer (ALB) with an Elastic IP address.
Why it's wrong here
ALB does not support Elastic IP; it uses a DNS name.
✗
Use Amazon Route 53 with a weighted routing policy.
Why it's wrong here
Route 53 is DNS, not a load balancer; does not provide a fixed IP.
✓
Use a Network Load Balancer (NLB) with an Elastic IP address.
Why this is correct
NLB supports Elastic IPs and is highly available across AZs.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a Classic Load Balancer (CLB) with an Elastic IP address.
Why it's wrong here
CLB supports Elastic IP but is a legacy option; NLB is more modern and recommended.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume an ALB can use Elastic IPs because it is a modern load balancer, but ALBs are DNS-based and cannot be assigned static IPs, making the NLB the only correct choice for fixed IP whitelisting with high availability.
Detailed technical explanation
How to think about this question
NLBs support static IP addresses by allowing you to assign one Elastic IP per Availability Zone subnet, which remains fixed even if the underlying instances change. This design meets the requirement for a fixed IP for partner firewalls while the NLB automatically distributes traffic across healthy targets in multiple AZs, ensuring high availability. Under the hood, the NLB uses a flow hash algorithm based on protocol, source IP, source port, destination IP, destination port, and TCP sequence number to maintain session stickiness without cookies.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Design for New Solutions — This question tests Design for New Solutions — 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 an Elastic IP address. — Option C is correct because a Network Load Balancer (NLB) supports static IP addresses via Elastic IPs per Availability Zone, providing a fixed IP for partner whitelisting while maintaining high availability across multiple AZs. Unlike ALBs, NLBs operate at Layer 4 and can preserve the client IP, which is critical for IP-based whitelisting scenarios.
What should I do if I get this SAP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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