The answer is to use a Network Load Balancer (NLB) with an Elastic IP address. This is correct because the NLB operates at Layer 4 and allows you to assign a static Elastic IP directly to each of its Availability Zone subnets, ensuring the IP address does not change over time. The NLB can then forward traffic to the Application Load Balancer (ALB) or directly to EC2 instances, preserving the existing application architecture while meeting the client whitelisting requirement. On the AWS Certified SAP on AWS Specialty PAS-C01 exam, this scenario tests your understanding of how to combine load balancer types to satisfy both static IP needs and Layer 7 routing—a common trap is assuming an ALB can be given a static IP, which it cannot. A useful memory tip: think of the NLB as the "fixed front door" with an Elastic IP, and the ALB as the "smart router" behind it.
PAS-C01 Migration Practice Question
This PAS-C01 practice question tests your understanding of migration. 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 that requires a static IP address for client whitelisting. The application will run on EC2 instances behind an Application Load Balancer (ALB). The company wants to ensure the IP address does not change over time. What should the company do?
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 D is correct because a Network Load Balancer (NLB) supports static IP addresses by allowing you to assign Elastic IPs directly to each of its Availability Zone subnets. This provides fixed IP endpoints for client whitelisting, while the NLB can forward traffic to the EC2 instances behind an ALB, preserving the application's architecture.
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.
✗
Assign an Elastic IP to each EC2 instance
Why it's wrong here
Clients would need to whitelist multiple IPs, and instances behind ALB are not directly accessed.
✗
Use Route 53 latency-based routing to point to the ALB
Why it's wrong here
ALB DNS name resolves to dynamic IPs; not suitable for static whitelisting.
✗
Use AWS Global Accelerator to get two static IP addresses
Why it's wrong here
Possible but overkill; NLB with Elastic IP is simpler and cost-effective.
✓
Use a Network Load Balancer (NLB) with an Elastic IP address
Why this is correct
NLB supports static IP via Elastic IP, which can be whitelisted.
Related concept
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 choose Global Accelerator because it offers static IPs, but they overlook that an NLB with Elastic IPs is the simpler, cost-effective solution for a single-region static IP requirement, and Global Accelerator is intended for global traffic acceleration, not just static IP assignment.
Detailed technical explanation
How to think about this question
An NLB operates at Layer 4 and preserves the client IP address by default, but when you assign an Elastic IP to the NLB, the source IP seen by the backend is the NLB's private IP unless you disable proxy protocol. In this scenario, the NLB can be placed in front of an ALB (using an internal ALB) to provide static IPs while retaining Layer 7 features; this is a common pattern for legacy applications that require IP whitelisting but need HTTP/HTTPS routing.
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.
Migration — This question tests Migration — 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 D is correct because a Network Load Balancer (NLB) supports static IP addresses by allowing you to assign Elastic IPs directly to each of its Availability Zone subnets. This provides fixed IP endpoints for client whitelisting, while the NLB can forward traffic to the EC2 instances behind an ALB, preserving the application's architecture.
What should I do if I get this PAS-C01 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A company is migrating a legacy application to AWS. The application requires a static IP address that must not change after migration. Which networking component should be used to ensure the application's public IP remains consistent?
medium
✓ A.Elastic IP address
B.Internet Gateway
C.VPC Peering
D.NAT Gateway
Why A: An Elastic IP address is a static public IPv4 address that can be associated with an EC2 instance or a Network Load Balancer. Option A (Internet Gateway) is used for VPC internet access but does not provide a static IP. Option B (NAT Gateway) is for outbound traffic. Option D (VPC Peering) is for connecting VPCs.
Variation 2. An organization is migrating a legacy application to AWS. The application requires a static IP address for client whitelisting. After migrating the application to an Application Load Balancer (ALB) with an Auto Scaling group, clients report connection failures. What should be done to resolve this issue?
hard
A.Place an Nginx reverse proxy in front of the ALB with an Elastic IP.
B.Assign an Elastic IP to the ALB.
C.Configure the ALB to use a round-robin routing algorithm.
✓ D.Replace the ALB with a Network Load Balancer (NLB) and assign an Elastic IP.
Why D: Option C is correct because an ALB does not have a static IP; using a Network Load Balancer (NLB) with an Elastic IP provides a static IP for whitelisting. Option A is wrong because an ALB cannot be assigned an Elastic IP. Option B is wrong because an ALB already distributes traffic. Option D is wrong because an Nginx proxy adds complexity and still requires a static IP.
Last reviewed: Jun 11, 2026
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This PAS-C01 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 PAS-C01 exam.
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