This ANS-C01 practice question tests your understanding of network design. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 has a VPC with a CIDR block of 10.0.0.0/16. They have a public subnet (10.0.1.0/24) and a private subnet (10.0.2.0/24). They have an internet gateway attached to the public subnet. They deploy a web server on an EC2 instance in the public subnet and a database on an EC2 instance in the private subnet. The database should only be accessible from the web server. The company wants to secure the database by not assigning a public IP address to it. Which configuration will allow the web server to connect to the database?
Create a VPC Peering connection between the public and private subnets
Why wrong: VPC Peering is not needed because subnets are in the same VPC.
B
Assign a public IP address to the database instance and configure the security group to allow inbound traffic from the web server's public IP
Why wrong: Assigning a public IP exposes the database to the internet.
C
Keep the database instance in the private subnet with no public IP, and configure the security group of the database to allow inbound traffic from the web server's security group on the database port
Instances can communicate via private IPs within the same VPC.
D
Set up a VPN connection between the web server and the database
Why wrong: VPN is for connecting on-premises networks to the VPC.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Keep the database instance in the private subnet with no public IP, and configure the security group of the database to allow inbound traffic from the web server's security group on the database port
Option C is correct because security groups in AWS can reference other security groups as a source, allowing traffic from any instance associated with the source security group. By configuring the database's security group to allow inbound traffic on the database port from the web server's security group, the web server can connect to the database without the database needing a public IP address. This leverages AWS's built-in security group chaining, which works across subnets 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.
✗
Create a VPC Peering connection between the public and private subnets
Why it's wrong here
VPC Peering is not needed because subnets are in the same VPC.
✗
Assign a public IP address to the database instance and configure the security group to allow inbound traffic from the web server's public IP
Why it's wrong here
Assigning a public IP exposes the database to the internet.
✓
Keep the database instance in the private subnet with no public IP, and configure the security group of the database to allow inbound traffic from the web server's security group on the database port
Why this is correct
Instances can communicate via private IPs within the same VPC.
Related concept
Read the scenario before looking for a memorised answer.
✗
Set up a VPN connection between the web server and the database
Why it's wrong here
VPN is for connecting on-premises networks to the VPC.
Common exam traps
Common exam trap: answer the scenario, not the keyword
AWS often tests the misconception that subnets in the same VPC need explicit routing or peering to communicate, but in reality, all subnets within a VPC are implicitly routable via the VPC's main route table, so security group configuration is the correct approach for access control.
Detailed technical explanation
How to think about this question
Security group referencing works by evaluating the source security group's network interfaces (ENIs) and allowing traffic based on the private IP addresses of those ENIs, even if the instances are in different subnets. This is more dynamic than using CIDR blocks because it automatically updates as instances are added or removed from the source security group. In real-world scenarios, this pattern is commonly used for multi-tier applications where the web tier must access the database tier without exposing the database to the internet or other VPC resources.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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: Keep the database instance in the private subnet with no public IP, and configure the security group of the database to allow inbound traffic from the web server's security group on the database port — Option C is correct because security groups in AWS can reference other security groups as a source, allowing traffic from any instance associated with the source security group. By configuring the database's security group to allow inbound traffic on the database port from the web server's security group, the web server can connect to the database without the database needing a public IP address. This leverages AWS's built-in security group chaining, which works across subnets 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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Question Discussion
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