ANS-C01 Network Design Practice Question
A company runs a multi-tier web application on AWS. The web servers in public subnets need to send traffic to the application servers in private subnets. The application servers must only accept traffic from the web servers. Both tiers are in the same VPC. Which design meets these requirements without introducing a single point of failure or unnecessary complexity?
⚠ Common exam trap
The trap here is that candidates often overcomplicate the solution by introducing load balancers or NAT gateways, or they incorrectly choose NACLs over security groups, not realizing that security group referencing provides a simpler, more dynamic, and more secure solution without single points of 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
✓
Place the web servers in a public subnet with a security group that allows inbound from 0.0.0.0/0 on port 443. Place the app servers in a private subnet with a security group that allows inbound from the web server security group on the application port.
It uses security group referencing, which allows the app servers' security group to dynamically allow traffic from any instance associated with the web servers' security group, regardless of IP address changes. This design avoids a single point of failure by not introducing any load balancer or gateway, and it minimizes complexity by leveraging native VPC security group behavior within the same VPC.
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 the web servers in a public subnet with a security group that allows inbound from 0.0.0.0/0 on port 443. Place the app servers in a private subnet with a security group that allows inbound from the web server security group on the application port.
Why this is correct
This is correct because it uses security group references for fine-grained, stateful filtering without introducing a single point of failure.
- ✗
Place the web servers and app servers in the same private subnet behind an internal Network Load Balancer. Route web traffic through the NLB.
Why it's wrong here
Introduces an NLB as a single point of failure and unnecessary component; also web servers need public access.
- ✗
Place the web servers in a public subnet with an Internet Gateway. Place the app servers in a private subnet with a NAT Gateway for outbound traffic. Use NACLs to allow inbound from the web subnet CIDR.
Why it's wrong here
NAT Gateway is for outbound traffic only and does not allow inbound from web servers; NACLs are stateless and add complexity.
- ✗
Place the web servers in a public subnet with a NACL allowing inbound on port 443. Place the app servers in a private subnet with a NACL allowing inbound from the web subnet CIDR on the application port.
Why it's wrong here
Using NACLs at the subnet level fails to meet the requirement for application servers to *only* accept traffic from the web servers. NACLs filter traffic based on subnet CIDRs, meaning any instance within the web subnet could reach the app servers, lacking the necessary instance-level granularity. This approach is tempting as NACLs provide a stateless, coarse-grained firewall for subnets, useful for broad traffic filtering or as an additional defence layer, but they cannot enforce instance-specific communication policies.
Visual reference
Go deeper
Related to this question
About these practice questions
This ANS-C01 question is part of Courseiva's 1,621-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
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.