The answer is to use multiple NAT gateways, one in each Availability Zone, alongside an Application Load Balancer with targets spread across multiple AZs. This design maximizes high availability across availability zones by eliminating any single point of failure at the network edge and load balancer layer; if one AZ fails, the ALB automatically reroutes traffic to healthy targets in remaining AZs, while the per-AZ NAT gateway ensures outbound connectivity remains intact. On the AWS Certified Advanced Networking Specialty ANS-C01 exam, this tests your understanding of fault isolation and regional versus zonal services—a common trap is assuming a single NAT gateway or a Network Load Balancer suffices, but the ALB’s regional nature is key for cross-AZ resilience. Remember the mnemonic: “ALB spreads, NAT per bed” to recall that the ALB distributes traffic across AZs and each AZ needs its own NAT gateway for true fault tolerance.
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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 is designing a network for a critical application that requires maximum availability. The application will be deployed across multiple Availability Zones in a single region. Which THREE design choices improve network availability?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use an Application Load Balancer with targets in multiple Availability Zones
An Application Load Balancer (ALB) with targets in multiple Availability Zones (AZs) improves availability by distributing incoming traffic across healthy targets in different AZs. If one AZ fails, the ALB automatically routes traffic to targets in the remaining AZs, ensuring the application remains accessible. This design eliminates a single point of failure at the load balancer level and leverages the regional nature of the ALB to provide cross-AZ fault tolerance.
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 with targets in multiple Availability Zones
Why this is correct
Distributes traffic across AZs.
Related concept
Read the scenario before looking for a memorised answer.
✓
Deploy EC2 instances in at least two Availability Zones
Why this is correct
Provides redundancy across AZs.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a single NAT gateway in one Availability Zone
Why it's wrong here
Single point of failure.
✗
Use a single subnet per Availability Zone
Why it's wrong here
Standard practice, not a high availability design choice.
✓
Use multiple NAT gateways, one in each Availability Zone
Why this is correct
Avoids single point of failure for outbound traffic.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that a single NATgateway is sufficient for high availability because it can route traffic from multiple AZs, but the trap here is that the NAT gateway itself is a zonal resource—if its AZ fails, all outbound traffic is lost, making it a critical single point of failure.
Detailed technical explanation
How to think about this question
Under the hood, an ALB operates at Layer 7 and maintains separate nodes in each enabled AZ, each with its own IP address. When you register targets across AZs, the ALB uses a round-robin or least outstanding requests algorithm to distribute traffic, and it performs health checks at the target level (e.g., HTTP 200 responses). In a real-world scenario, if an AZ suffers a power outage, the ALB automatically removes that AZ's targets from its routing table within seconds, preventing traffic from being sent to unreachable instances. This behavior is governed by the ALB's cross-zone load balancing setting, which is enabled by default.
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
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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.
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Use an Application Load Balancer with targets in multiple Availability Zones — An Application Load Balancer (ALB) with targets in multiple Availability Zones (AZs) improves availability by distributing incoming traffic across healthy targets in different AZs. If one AZ fails, the ALB automatically routes traffic to targets in the remaining AZs, ensuring the application remains accessible. This design eliminates a single point of failure at the load balancer level and leverages the regional nature of the ALB to provide cross-AZ fault tolerance.
What should I do if I get this ANS-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
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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 designing a network for a critical application that requires high availability across multiple Availability Zones. Which TWO design choices ensure that the application remains available if an entire AZ fails?
medium
A.Deploy resources in a single Availability Zone.
✓ B.Deploy resources in at least two Availability Zones.
C.Use a Network Load Balancer in a single AZ.
✓ D.Use an Application Load Balancer that spans multiple AZs.
E.Use a single EC2 instance with an Elastic IP address.
Why B: Options B and D are correct. Deploying resources across at least two AZs (B) ensures that if one AZ fails, the other continues to operate. Using an Application Load Balancer (D) distributes traffic across healthy targets in multiple AZs, automatically rerouting traffic away from failed AZs. Option A is wrong because a single AZ is a single point of failure. Option C is wrong because a Network Load Balancer can also provide high availability, but the question asks for TWO choices; B and D are the most common design. Option E is wrong because a single EC2 instance cannot provide high availability.
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This ANS-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 ANS-C01 exam.
Question Discussion
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