ANS-C01 Network Design Practice Question
A company is designing a VPC for a three-tier application (web, application, database). The database tier should not be accessible from the internet, but the web tier must be accessible. Which subnet design should the network engineer use?
⚠ Common exam trap
Test-takers frequently assume placing all servers in private subnets with a NAT Gateway provides inbound internet access, confusing outbound-only NAT with the inbound access required for the web tier, or they mistakenly think security groups alone can fully replace subnet-level isolation in a public subnet.
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 web servers in public subnets with an internet gateway, and app and database servers in private subnets.
It places the web servers in a public subnet with an Internet Gateway (IGW) to allow inbound HTTP/HTTPS traffic from the internet, while the application and database servers are placed in private subnets with no direct internet path. This design ensures the database tier is isolated from the internet, meeting the security requirement, while the web tier remains accessible. The application servers can communicate with the database via private IP addresses within the VPC, and outbound internet access for the private subnets (if needed) can be provided through a NAT Gateway in a public subnet.
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 web and app servers in public subnets, and database servers in private subnets.
Why it's wrong here
App servers should not be directly exposed to the internet.
- ✗
Place all servers in private subnets and use a NAT Gateway for internet access.
Why it's wrong here
Private subnets cannot receive inbound traffic from the internet without a load balancer in a public subnet.
- ✓
Place web servers in public subnets with an internet gateway, and app and database servers in private subnets.
Why this is correct
This follows the traditional security model of isolation for backend tiers.
- ✗
Place all servers in public subnets and rely on security group rules to restrict access.
Why it's wrong here
Public subnets have direct routes to the internet gateway, increasing attack surface.
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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.