ANS-C01 Network Design Practice Question
A company is deploying a new application on AWS and needs a highly available architecture across two Availability Zones (AZs) in a single region. The application consists of an Application Load Balancer (ALB) in front of a fleet of EC2 instances running in an Auto Scaling group, and an Amazon RDS for MySQL database with Multi-AZ deployment. The company requires that the application remain available even if an entire AZ fails. The network team has designed the VPC with two public subnets and two private subnets, each in a different AZ. The ALB is internet-facing and placed in the public subnets. The EC2 instances are in the private subnets. The RDS instance is also in the private subnets. The route tables are configured with a default route via an Internet Gateway for public subnets and via a NAT Gateway for private subnets. What change is MOST likely needed to ensure the architecture can survive an AZ failure?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a NAT Gateway in each Availability Zone
To survive an AZ failure, each AZ must have its own NAT Gateway to provide outbound internet access for instances in that AZ. If only one NAT Gateway is used and its AZ fails, instances in the other AZ lose internet connectivity. The architecture already has the ALB in public subnets across both AZs and RDS Multi-AZ, so the missing component is a NAT Gateway per AZ. Option A is incorrect because you cannot have an Internet Gateway per AZ; it is a regional resource. Option B is incorrect because an NLB is not needed; the ALB already provides load balancing. Option D is incorrect because the Auto Scaling group should already be configured to launch instances in both AZs; that's a prerequisite, not the most likely missing change.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Add a second Internet Gateway in the other AZ
Why it's wrong here
One Internet Gateway per VPC is sufficient; it is a highly available service.
- ✗
Use a Network Load Balancer instead of an Application Load Balancer
Why it's wrong here
ALB is already highly available across AZs; NLB is not needed for this issue.
- ✓
Create a NAT Gateway in each Availability Zone
Why this is correct
A NAT Gateway per AZ ensures outbound connectivity survives an AZ failure.
- ✗
Configure the Auto Scaling group to launch instances in both AZs
Why it's wrong here
This is already likely configured; the question implies it's set up.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.