- A
Place an internet-facing Application Load Balancer (ALB) in public subnets across two Availability Zones.
Provides high availability and internet access for the web tier.
- B
Configure the web tier EC2 instances in an Auto Scaling group across two Availability Zones.
Auto Scaling group across multiple AZs provides high availability and scalability.
- C
Use a stateful network ACL for the web tier subnets to simplify security rules.
Why wrong: NACLs are stateless; security groups are stateful.
- D
Deploy a NAT Gateway in a single Availability Zone for outbound traffic from private subnets.
Why wrong: A single NAT Gateway is a single point of failure; should deploy one per AZ for high availability.
- E
Create the VPC with a single Availability Zone to simplify management.
Why wrong: Single AZ is not highly available; should use at least two AZs.
Achieving High Availability for a Three-Tier Web Application Using ALB and Auto Scaling Across AZs
This ANS-C01 practice question tests your understanding of network implementation. 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 three-tier web application on AWS. The web tier must be accessible from the internet, and the application and database tiers must be in private subnets. The company wants to use a single AWS Region and ensure high availability. Which TWO configurations should be implemented? (Choose two.)
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
Place an internet-facing Application Load Balancer (ALB) in public subnets across two Availability Zones.
Option A is correct because an internet-facing Application Load Balancer (ALB) in public subnets across two Availability Zones (AZs) provides both internet access to the web tier and high availability. The ALB distributes incoming HTTP/HTTPS traffic to web instances in private subnets, and deploying across two AZs ensures fault tolerance if one AZ fails.
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.
- ✓
Place an internet-facing Application Load Balancer (ALB) in public subnets across two Availability Zones.
Why this is correct
Provides high availability and internet access for the web tier.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
Configure the web tier EC2 instances in an Auto Scaling group across two Availability Zones.
Why this is correct
Auto Scaling group across multiple AZs provides high availability and scalability.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use a stateful network ACL for the web tier subnets to simplify security rules.
Why it's wrong here
NACLs are stateless; security groups are stateful.
- ✗
Deploy a NAT Gateway in a single Availability Zone for outbound traffic from private subnets.
- ✗
Create the VPC with a single Availability Zone to simplify management.
Why it's wrong here
Single AZ is not highly available; should use at least two AZs.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse stateless network ACLs with stateful security groups, leading them to incorrectly select option C, or they assume a single NAT Gateway is sufficient for high availability, overlooking the need for redundancy in each AZ.
Detailed technical explanation
How to think about this question
An internet-facing ALB operates at Layer 7 and terminates TLS, offloading encryption from web servers. It uses health checks to route traffic only to healthy targets, and cross-zone load balancing distributes requests evenly across instances in all AZs. In a multi-AZ setup, the ALB’s DNS name resolves to multiple IP addresses, one per AZ, enabling automatic failover if an AZ becomes unavailable.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
Visual reference
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Implementation — This question tests Network Implementation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Place an internet-facing Application Load Balancer (ALB) in public subnets across two Availability Zones. — Option A is correct because an internet-facing Application Load Balancer (ALB) in public subnets across two Availability Zones (AZs) provides both internet access to the web tier and high availability. The ALB distributes incoming HTTP/HTTPS traffic to web instances in private subnets, and deploying across two AZs ensures fault tolerance if one AZ fails.
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.
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Same concept, more angles
1 more ways this is tested on ANS-C01
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 has a VPC (10.0.0.0/16) with two subnets: public (10.0.1.0/24) and private (10.0.2.0/24). They have an Application Load Balancer (ALB) in the public subnet that distributes traffic to EC2 instances in the private subnet. The ALB is internet-facing and has a security group that allows inbound HTTP/S from 0.0.0.0/0. The EC2 instances have a security group that allows inbound HTTP from the ALB's security group. Users report that they can access the application, but the application is slow and sometimes times out. The network engineer checks CloudWatch metrics and sees that the ALB's target response time is high. The engineer suspects that the EC2 instances are overwhelmed. Which action should the engineer take to improve performance?
hard- A.Add a NAT gateway in the public subnet to reduce latency.
- B.Replace the ALB with a Network Load Balancer to reduce overhead.
- C.Increase the size of the EC2 instances in the private subnet.
- ✓ D.Add EC2 instances in another Availability Zone and register them with the ALB.
Why D: Option D is correct because adding EC2 instances in another Availability Zone increases capacity and distributes traffic across multiple AZs, reducing the load on each instance and improving performance and fault tolerance. Option A is incorrect because a NAT gateway is for outbound internet access, not for reducing latency between ALB and targets. Option B is incorrect because an NLB does not automatically distribute traffic across AZs as effectively for HTTP applications and does not offload processing. Option C is incorrect because simply increasing instance size (vertical scaling) may not provide the same benefits as horizontal scaling across AZs for handling variable loads.
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Last reviewed: Jun 11, 2026
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.
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