The correct answer is that the workload account must configure security groups for the EC2 instance to allow traffic to the RDS database’s security group. This is because when a subnet is shared via AWS Resource Access Manager (RAM), the VPC owner retains control over the route tables and network ACLs, while the participant account can only manage its own security groups to control traffic to and from its resources. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of the shared subnet RAM security group configuration model, where participant accounts have limited network control but full security group autonomy. A common trap is assuming the participant can modify route tables or that VPC peering is needed, but the correct approach leverages security groups as the sole traffic filter the participant can adjust. Memory tip: think “RAM gives you the subnet, but you bring your own security group rules.”
SAP-C02 Practice Question: Design Solutions for Organizational Complexity
This SAP-C02 practice question tests your understanding of design solutions for organizational complexity. 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.
Network Topology
A company uses AWS Organizations and has shared a subnet from the VPC shown in the exhibit using AWS Resource Access Manager (RAM). A workload account launches an EC2 instance in the shared subnet. The instance needs to communicate with an RDS database in a different private subnet within the same VPC. What additional configuration is required?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The workload account must configure security groups for the EC2 instance to allow traffic to the RDS database's security group.
Option C is correct. When a subnet is shared, the owner account manages the route tables and network ACLs, but the participant account cannot modify them. However, the participant account can use security groups to control traffic to/from its instances. Therefore, the workload account must configure security groups to allow traffic between the EC2 instance and the RDS database. Option A is wrong because VPC peering is not needed; the VPC is already shared. Option B is wrong because the route table is managed by the owner, not the participant. Option D is wrong because transit gateway is not needed.
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 workload account must create a route table entry in the shared VPC to allow communication.
Why it's wrong here
The workload account cannot modify route tables in the shared VPC.
✓
The workload account must configure security groups for the EC2 instance to allow traffic to the RDS database's security group.
Why this is correct
Security groups are managed by the account that owns the resource.
Establish a VPC peering connection between the workload account's VPC and the shared VPC.
Why it's wrong here
The workload account already has access to the shared VPC via the shared subnet.
✗
Attach an AWS Transit Gateway to both VPCs to enable communication.
Why it's wrong here
Transit gateway is unnecessary as both resources are in the same VPC.
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: The workload account must configure security groups for the EC2 instance to allow traffic to the RDS database's security group. — Option C is correct. When a subnet is shared, the owner account manages the route tables and network ACLs, but the participant account cannot modify them. However, the participant account can use security groups to control traffic to/from its instances. Therefore, the workload account must configure security groups to allow traffic between the EC2 instance and the RDS database. Option A is wrong because VPC peering is not needed; the VPC is already shared. Option B is wrong because the route table is managed by the owner, not the participant. Option D is wrong because transit gateway is not needed.
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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