The correct choice is to deploy a Network Load Balancer with Elastic IPs in front of NAT instances in each Availability Zone, because this architecture combines a fixed outbound IP with true high availability. The NLB, using its Elastic IPs as static source addresses, distributes traffic across NAT instances in multiple AZs, so if one AZ fails, the NLB seamlessly routes traffic to healthy NAT instances in another AZ, preserving the same whitelisted IP for external partners. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how to decouple IP stability from single-AZ dependencies, a common trap being that NAT gateways offer fixed IPs but only per-AZ, while multiple NAT gateways produce different IPs. A key memory tip: think “NLB + NAT instances = fixed IP with AZ fault tolerance,” contrasting with NAT gateways which are AZ-locked.
SAP-C02 Continuous Improvement for Existing Solutions Practice Question
This SAP-C02 practice question tests your understanding of continuous improvement for existing solutions. 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 company runs a critical workload on EC2 instances in an Auto Scaling group across three Availability Zones. The application needs to maintain a consistent IP address for outbound traffic to external partners. The current design uses a NAT gateway in each AZ, but partners whitelist a single IP. How can the company provide a fixed outbound IP while maintaining high availability?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deploy a Network Load Balancer with Elastic IPs in front of NAT instances in each AZ.
Option C is correct because a NATgateway with an Elastic IP can be placed in a single AZ, but if that AZ fails, the workload fails. A Network Load Balancer with EIPs and NAT instances provides a fixed IP and HA. Option A is wrong because multiple NAT gateways have different IPs. Option B is wrong because it's not HA. Option D is wrong because a proxy fleet still uses multiple IPs.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 a proxy fleet of EC2 instances behind an Application Load Balancer.
Why it's wrong here
ALB does not provide a single static outbound IP.
✗
Use a single NAT gateway across all three AZs and assign an Elastic IP.
Why it's wrong here
A NATgateway is AZ-resilient only within its zone; cross-AZ routing is not supported.
✗
Use a NAT instance with an Elastic IP in one AZ.
Why it's wrong here
Single point of failure.
✓
Deploy a Network Load Balancer with Elastic IPs in front of NAT instances in each AZ.
Why this is correct
NLB provides a static IP and distributes traffic to NAT instances across AZs for HA.
Related concept
Static NAT maps one inside address to one outside address.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
Continuous Improvement for Existing Solutions — This question tests Continuous Improvement for Existing Solutions — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: Deploy a Network Load Balancer with Elastic IPs in front of NAT instances in each AZ. — Option C is correct because a NAT gateway with an Elastic IP can be placed in a single AZ, but if that AZ fails, the workload fails. A Network Load Balancer with EIPs and NAT instances provides a fixed IP and HA. Option A is wrong because multiple NAT gateways have different IPs. Option B is wrong because it's not HA. Option D is wrong because a proxy fleet still uses multiple IPs.
What should I do if I get this SAP-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SAP-C02 NAT questions on configuration and troubleshooting.
What is the key concept behind this question?
Static NAT maps one inside address to one outside address.
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