- A
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.
This is correct because it uses security group references for fine-grained, stateful filtering without introducing a single point of failure.
- B
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 wrong: Introduces an NLB as a single point of failure and unnecessary component; also web servers need public access.
- C
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 wrong: NAT Gateway is for outbound traffic only and does not allow inbound from web servers; NACLs are stateless and add complexity.
- D
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 wrong: NACLs are stateless and require separate inbound and outbound rules; also more complex to manage than security groups.
ANS-C01 Network Design Practice Question
This ANS-C01 practice question tests your understanding of network design. 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 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?
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.
Option A is correct because 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.
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 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.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
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.
- ✗
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
NACLs are stateless and require separate inbound and outbound rules; also more complex to manage than security groups.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
Security group referencing works by allowing traffic based on the security group ID, not the IP address, so if web server instances are replaced or scaled, the app server security group automatically permits traffic from the new instances. This is possible because security groups are stateful, meaning return traffic is automatically allowed, unlike NACLs which require explicit outbound rules. In real-world scenarios, this design is preferred for multi-tier applications within a VPC because it simplifies management and avoids the overhead of maintaining IP-based rules.
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.
What to study next
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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. — Option A is correct because 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.
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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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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