The answer is to configure the RDS security group to allow inbound traffic from the member account VPC CIDRs and to use an AWS Transit Gateway to route traffic between the shared services and member account VPCs. This is correct because security groups act as a virtual firewall for the central RDS instance, and explicitly allowing traffic from known member VPC ranges ensures that only authorized network paths can reach the database. Transit Gateway is necessary because VPC peering is not transitive, so a hub-and-spoke model with Transit Gateway efficiently connects multiple member VPCs to the shared services VPC without complex peering mesh. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of centralized database access patterns in a multi-account architecture, often appearing as a trap where candidates mistakenly choose VPC peering or direct Lambda access. A key memory tip: remember that security groups are stateful and allow traffic based on source CIDR, while Transit Gateway replaces non-transitive peering for central RDS access from multiple accounts.
SAP-C02 Practice Question: Design Solutions for Organizational Complexity
This SAP-C02 practice question tests your understanding of design solutions for organizational complexity. 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 has a multi-account architecture with a shared services account that hosts a central Amazon RDS instance. Member accounts need to access this database. Which TWO actions should the company take to enable secure access?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a Transit Gateway and attach all VPCs to it, then use route tables to enable connectivity.
Options A and D are correct. Option B is wrong because VPC peering is not transitive; a Transit Gateway handles many VPCs. Option C is wrong because direct Lambda access would bypass security groups. Option E is wrong because the RDS should not be public.
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.
✓
Create a Transit Gateway and attach all VPCs to it, then use route tables to enable connectivity.
Make the RDS instance publicly accessible and use IAM authentication.
Why it's wrong here
Security risk; prefer private connectivity.
✗
Create a VPC peering connection between each member VPC and the shared services VPC.
Why it's wrong here
VPC peering is not transitive; a Transit Gateway is better for many VPCs.
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 SAP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Design Solutions for Organizational Complexity — This question tests Design Solutions for Organizational Complexity — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create a Transit Gateway and attach all VPCs to it, then use route tables to enable connectivity. — Options A and D are correct. Option B is wrong because VPC peering is not transitive; a Transit Gateway handles many VPCs. Option C is wrong because direct Lambda access would bypass security groups. Option E is wrong because the RDS should not be public.
What should I do if I get this SAP-C02 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related SAP-C02 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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