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SDLC Automation →hardMultiple ChoiceObjective-mapped

Quick Answer

The correct answer is that the security group for the RDS database does not allow inbound traffic from the security group assigned to the CodeBuild project. This is because CodeBuild, when configured with VPC support, runs inside your VPC and its build containers are assigned a security group; for the database to accept connections, its inbound rules must explicitly permit traffic from that CodeBuild security group, typically on the database port. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of VPC networking and security group chaining, a common trap being that candidates focus on outbound rules or internet gateway requirements rather than the bidirectional nature of security group traffic. A key memory tip is “inbound for the receiver, outbound for the requester”—the database’s security group must allow inbound from CodeBuild, while CodeBuild’s security group must allow outbound to the database.

DOP-C02 SDLC Automation Practice Question

This DOP-C02 practice question tests your understanding of sdlc automation. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 team uses AWS CodeBuild to run integration tests that require access to an Amazon RDS database. The database is in a private subnet. The CodeBuild project is configured to use a VPC. However, the builds are failing with a timeout connecting to the database. What could be the issue?

Question 1hardmultiple choice

Review the full subnetting walkthrough →

A
The CodeBuild project's VPC configuration does not include the subnet IDs where the database resides.
Why wrong: CodeBuild requires both VPC ID and subnet IDs.
B
The security group for the CodeBuild project does not allow outbound traffic to the RDS database.
Why wrong: Outbound rules are typically allow-all; inbound rules on the database side are the issue.
C
The security group for the RDS database does not allow inbound traffic from the security group assigned to the CodeBuild project.
The database's security group must allow inbound from the CodeBuild security group.
D
The CodeBuild project does not have a route to the internet via an internet gateway, so it cannot reach the RDS endpoint.
Why wrong: RDS in a private subnet does not require internet access; it can be reached via VPC routing.

Full breakdown with real-world context →

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

✓

The security group for the RDS database does not allow inbound traffic from the security group assigned to the CodeBuild project.

Option B is correct because security group rules must allow inbound traffic from the security group associated with the CodeBuild project. Option A is wrong because CodeBuild VPC support requires subnets, not just the VPC ID. Option C is wrong because CodeBuild does not need an internet gateway for VPC-based builds; it can use VPC endpoints for AWS services. Option D is wrong because the security group for CodeBuild should allow outbound to the database, but the database's security group must allow inbound from CodeBuild.

Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

Answer analysis

Option-by-option breakdown

For each option: why learners choose it and why it is or isn't the right answer here.

✗
The CodeBuild project's VPC configuration does not include the subnet IDs where the database resides.
Why it's wrong here
CodeBuild requires both VPC ID and subnet IDs.
✗
The security group for the CodeBuild project does not allow outbound traffic to the RDS database.
Why it's wrong here
Outbound rules are typically allow-all; inbound rules on the database side are the issue.
✓
The security group for the RDS database does not allow inbound traffic from the security group assigned to the CodeBuild project.
Why this is correct
The database's security group must allow inbound from the CodeBuild security group.
Related concept
CIDR notation defines the prefix length.
✗
The CodeBuild project does not have a route to the internet via an internet gateway, so it cannot reach the RDS endpoint.
Why it's wrong here
RDS in a private subnet does not require internet access; it can be reached via VPC routing.

Common exam traps

Common exam trap: usable hosts are not the same as total addresses

Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.

Detailed technical explanation

How to think about this question

Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.

KKey Concepts to Remember

CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.

TExam Day Tips

Write the block size before choosing the subnet.
Check whether the question asks for hosts, subnets or a specific address range.
Do not confuse /24, /25, /26 and /27 host counts.

Key takeaway

Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.

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.

Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related DOP-C02 subnetting questions on CIDR, address ranges, and subnet selection.

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FAQ

Questions learners often ask

What does this DOP-C02 question test?

SDLC Automation — This question tests SDLC Automation — CIDR notation defines the prefix length..

What is the correct answer to this question?

The correct answer is: The security group for the RDS database does not allow inbound traffic from the security group assigned to the CodeBuild project. — Option B is correct because security group rules must allow inbound traffic from the security group associated with the CodeBuild project. Option A is wrong because CodeBuild VPC support requires subnets, not just the VPC ID. Option C is wrong because CodeBuild does not need an internet gateway for VPC-based builds; it can use VPC endpoints for AWS services. Option D is wrong because the security group for CodeBuild should allow outbound to the database, but the database's security group must allow inbound from CodeBuild.

What should I do if I get this DOP-C02 question wrong?

What is the key concept behind this question?

CIDR notation defines the prefix length.

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Last reviewed: Jun 20, 2026

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