- A
An inbound rule in the database's security group that allows traffic from the web server's private IP address.
Why wrong: Using private IP is not scalable; use security group reference.
- B
An inbound rule in the database's security group that references the web server's security group.
Allows traffic from any instance with that SG.
- C
An internet gateway attached to the VPC.
Why wrong: Not required for internal VPC communication.
- D
A route table associated with the private subnet that includes a route to the public subnet's CIDR block via the local route.
Local routes are automatically added, so this is implicitly satisfied.
- E
A NAT gateway in the public subnet.
Why wrong: Not required for internal VPC communication.
Question 1,059 of 1,705
Security Group Referencing for Database Access in VPC
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 VPC with a public subnet and a private subnet. The private subnet hosts an RDS database, and the public subnet hosts a web server. The web server needs to access the database. Which TWO of the following are required to allow the web server to connect to the database?
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
✓
An inbound rule in the database's security group that references the web server's security group.
Option B is correct because security group rules can reference other security groups as a source, allowing traffic from any instance associated with the referenced security group (the web server's security group) without needing to specify individual IP addresses. This is the recommended AWS best practice for inter-instance communication within a VPC, as it dynamically adapts to changes in the web server's IP or scaling events.
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.
- ✗
An inbound rule in the database's security group that allows traffic from the web server's private IP address.
Why it's wrong here
Using private IP is not scalable; use security group reference.
- ✓
An inbound rule in the database's security group that references the web server's security group.
Why this is correct
Allows traffic from any instance with that SG.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
An internet gateway attached to the VPC.
Why it's wrong here
Not required for internal VPC communication.
- ✓
A route table associated with the private subnet that includes a route to the public subnet's CIDR block via the local route.
Why this is correct
Local routes are automatically added, so this is implicitly satisfied.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
A NAT gateway in the public subnet.
Why it's wrong here
Not required for internal VPC communication.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the misconception that a NAT gateway or internet gateway is required for any cross-subnet communication, but the trap here is that traffic between subnets within the same VPC uses the local route and does not require any gateway.
Detailed technical explanation
How to think about this question
When a security group rule references another security group, AWS evaluates the rule by checking the source IP of the incoming packet against the private IP addresses of all instances associated with the referenced security group. This works because the VPC's implicit router uses the local route (the VPC's CIDR) to forward traffic between subnets, and the database's security group statefully tracks the connection, allowing return traffic automatically. In real-world scenarios, this approach simplifies management when web servers are auto-scaled, as new instances inherit the security group and gain access without updating 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 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.
Visual reference
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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: An inbound rule in the database's security group that references the web server's security group. — Option B is correct because security group rules can reference other security groups as a source, allowing traffic from any instance associated with the referenced security group (the web server's security group) without needing to specify individual IP addresses. This is the recommended AWS best practice for inter-instance communication within a VPC, as it dynamically adapts to changes in the web server's IP or scaling events.
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: Jul 4, 2026
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