The answer is to use a Network Load Balancer (NLB) with Elastic IP addresses assigned to each subnet. This is correct because an NLB operates at Layer 4 and allows you to associate a static Elastic IP directly with each Availability Zone, providing a fixed IP address that remains unchanged even when backend instances are replaced or scaled. For the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how to meet strict whitelisting requirements while maintaining high availability across multiple AZs—a common trap is choosing an Application Load Balancer, which lacks static IP support, or assuming a single Elastic IP can cover all zones. Remember the key distinction: only NLB supports static IPs per AZ via Elastic IP assignment, whereas ALB and CLB do not. A useful memory tip is "NLB = No Loss of IP," reinforcing that the IP stays fixed regardless of instance churn.
SAP-C02 Practice Question: Design Solutions for Organizational Complexity
This SAP-C02 practice question tests your understanding of design solutions for organizational complexity. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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 application to AWS. The application requires a static IP address that can be used for whitelisting by third-party partners. The application will be deployed in multiple Availability Zones for high availability. The company wants to use a load balancer to distribute traffic. The solution must provide a single static IP address that does not change even if the underlying instances are replaced. Which combination of services should the company 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 Elastic IP addresses assigned to each subnet.
Option D is correct because a Network Load Balancer (NLB) supports static IP addresses by allowing you to assign Elastic IP addresses to each Availability Zone subnet. This provides a single static IP per AZ that does not change even when backend instances are replaced, meeting the requirement for a fixed whitelisting address across multiple AZs.
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 a static Elastic IP address attached to the ALB.
Why it's wrong here
ALBs do not support attaching Elastic IPs directly.
✗
Use AWS Global Accelerator with an ALB as the endpoint.
Why it's wrong here
Global Accelerator provides static IPs, but the question asks for a load balancer; this is a valid solution but not the most direct.
✗
Use Amazon CloudFront with an ALB as the origin.
Why it's wrong here
CloudFront provides static IPs but is for content delivery.
✓
Use a Network Load Balancer (NLB) with Elastic IP addresses assigned to each subnet.
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume an ALB can have a static IP attached because it is a common load balancer, but ALBs are Layer 7 and inherently use dynamic IPs, while only NLBs (Layer 4) support Elastic IP assignment per subnet.
Detailed technical explanation
How to think about this question
An NLB operates at Layer 4 (TCP/UDP) and preserves the client IP address, which is critical for whitelisting scenarios. When you assign Elastic IPs to each NLB subnet, the NLB uses those IPs as the source IP for outgoing traffic and the destination IP for incoming traffic, ensuring the static IP remains constant even during instance replacement or scaling events. This is distinct from ALBs, which use dynamic IPs behind a DNS name and cannot guarantee a fixed IP for whitelisting.
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 Solutions for Organizational Complexity — This question tests Design Solutions for Organizational Complexity — 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 Elastic IP addresses assigned to each subnet. — Option D is correct because a Network Load Balancer (NLB) supports static IP addresses by allowing you to assign Elastic IP addresses to each Availability Zone subnet. This provides a single static IP per AZ that does not change even when backend instances are replaced, meeting the requirement for a fixed whitelisting address across multiple AZs.
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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