← ANS-C01·Amazon Web Services

Question 163 of 1,705

Network Implementation →mediumMultiple SelectObjective-mapped

Secure Multi-Tier Web Application: ALB in Public Subnet, Private Tiers with Security Groups

This ANS-C01 practice question tests your understanding of network implementation. 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 designing a multi-tier application in a VPC. The web tier must be accessible from the internet, while the application tier must only be accessible from the web tier. The database tier must be isolated from all other tiers except the application tier. Which TWO network architectures meet these requirements? (Choose TWO.)

A
Use a single public subnet for all tiers and control access with security groups.
Why wrong: All instances would have public IPs, exposing app and database to the internet.
B
Use private subnets for all tiers and a NAT gateway for internet access from the web tier. Use security groups to control traffic.
Why wrong: No inbound internet access to web tier unless an ALB is in a public subnet.
C
Use a public subnet for an Application Load Balancer and private subnets for web, app, and database tiers. Use security groups to restrict traffic between tiers.
The ALB in public subnet provides inbound access; private subnets isolate tiers.
D
Use a VPN connection from the on-premises network to access all tiers.
Why wrong: This does not address internet access for the web tier.
E
Use public subnets for the web tier, private subnets for the application tier, and isolated subnets (no route to internet) for the database tier. Use security groups to allow traffic only from the web to app and app to database.
This provides proper isolation and access control.

Full breakdown with real-world context →

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

✓

Use a public subnet for an Application Load Balancer and private subnets for web, app, and database tiers. Use security groups to restrict traffic between tiers.

Option C is correct because it places the Application Load Balancer in a public subnet to receive internet traffic, while the web, app, and database tiers reside in private subnets. Security groups are used to restrict traffic flows: the ALB security group allows inbound HTTP/HTTPS from the internet, the web tier security group allows inbound only from the ALB, the app tier security group allows inbound only from the web tier, and the database tier security group allows inbound only from the app tier. This ensures the application tier is only accessible from the web tier, and the database tier is isolated except from the application tier.

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 a single public subnet for all tiers and control access with security groups.
Why it's wrong here
All instances would have public IPs, exposing app and database to the internet.
✗
Use private subnets for all tiers and a NAT gateway for internet access from the web tier. Use security groups to control traffic.
Why it's wrong here
No inbound internet access to web tier unless an ALB is in a public subnet.
✓
Use a public subnet for an Application Load Balancer and private subnets for web, app, and database tiers. Use security groups to restrict traffic between tiers.
Why this is correct
The ALB in public subnet provides inbound access; private subnets isolate tiers.
Related concept
Read the scenario before looking for a memorised answer.
✗
Use a VPN connection from the on-premises network to access all tiers.
Why it's wrong here
This does not address internet access for the web tier.
✓
Use public subnets for the web tier, private subnets for the application tier, and isolated subnets (no route to internet) for the database tier. Use security groups to allow traffic only from the web to app and app to database.
Why this is correct
This provides proper isolation and access control.
Related concept
Read the scenario before looking for a memorised answer.

Common exam traps

Common exam trap: answer the scenario, not the keyword

The ANS-C01 exam often tests the misconception that placing all tiers in private subnets with a NAT gateway can provide inbound internet access, but a NAT gateway only supports outbound-initiated traffic and cannot accept inbound connections from the internet.

Detailed technical explanation

How to think about this question

In a multi-tier VPC architecture, security groups act as stateful virtual firewalls that evaluate inbound and outbound rules at the instance level. When using an Application Load Balancer in a public subnet, it terminates the client connection and initiates a new connection to the web tier instances, allowing the web tier to remain in a private subnet without a public IP. The database tier can be placed in an isolated subnet (no route to an internet gateway or NAT gateway) to ensure it has no internet connectivity at all, which is a common pattern for compliance with standards like PCI DSS.

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

What to study next

Got this wrong? Here's your next step.

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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: Use a public subnet for an Application Load Balancer and private subnets for web, app, and database tiers. Use security groups to restrict traffic between tiers. — Option C is correct because it places the Application Load Balancer in a public subnet to receive internet traffic, while the web, app, and database tiers reside in private subnets. Security groups are used to restrict traffic flows: the ALB security group allows inbound HTTP/HTTPS from the internet, the web tier security group allows inbound only from the ALB, the app tier security group allows inbound only from the web tier, and the database tier security group allows inbound only from the app tier. This ensures the application tier is only accessible from the web tier, and the database tier is isolated except from the application tier.

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 is deploying a multi-tier web application in a VPC. The web tier must be accessible from the internet, while the application tier must only be accessible from the web tier. The database tier must only be accessible from the application tier. Which design best meets these requirements?

medium

A.Place all tiers in public subnets and use security groups to control traffic between tiers.
✓ B.Place the web tier in public subnets with an internet gateway, and the application and database tiers in private subnets. Use security groups to allow traffic from the web tier to the application tier, and from the application tier to the database tier.
C.Place all tiers in the same subnet and use network ACLs to restrict traffic between tiers.
D.Place the web tier in a private subnet and use a NAT gateway for outbound internet access. Place the application and database tiers in public subnets.

Why B: Option B is correct because it places the web tier in a public subnet with an Internet Gateway (IGW) for direct internet access, while the application and database tiers reside in private subnets with no direct internet path. Security groups act as stateful virtual firewalls at the instance level, allowing you to specify inbound rules that permit traffic only from the web tier security group to the application tier, and from the application tier security group to the database tier. This layered approach enforces the principle of least privilege and meets the access requirements without exposing the internal tiers to the internet.

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