The correct answer is to create a separate VPC for each service, with VPC peering only between the API gateway and each service VPC. This design achieves true microservices isolation by enforcing network-level boundaries, ensuring that each service’s DynamoDB table is inaccessible from any other service’s VPC. Because VPC peering is established exclusively for API communication, no direct database access path exists between services, which prevents any unintended traffic even if a security group misconfiguration occurs. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of how to combine VPC isolation with controlled peering to meet strict compliance requirements, often appearing as a trap where candidates mistakenly choose a shared VPC with security groups or subnets. The key trap is assuming that security groups alone provide sufficient isolation, but they cannot prevent routing between subnets in the same VPC. Memory tip: think “separate VPCs, peering only for APIs” to remember that network isolation requires distinct VPCs, not just logical separation within one.
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. 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 microservices architecture on AWS. Each service needs its own DynamoDB table, and services must be fully isolated. Which networking design ensures that services can only communicate through APIs and not directly to each other's databases?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Create a separate VPC for each service, with VPC peering only between the API gateway and each service VPC.
Placing services in separate VPCs with VPC peering only for API communication ensures network-level isolation. Option B is correct because it prevents direct database access by not allowing peering between all VPCs. Option A is wrong because a shared VPC with security groups could allow unintended traffic. Option C is wrong because a single VPC with subnets still allows routing between services. Option D is wrong because a transit VPN does not provide the needed isolation.
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.
✗
Place all services in a single VPC with security groups to control traffic.
Why it's wrong here
Security groups are stateful and could be misconfigured, allowing direct database access.
✗
Use a transit VPC with VPN connections to each service's VPC.
Why it's wrong here
This still allows potential direct communication between service VPCs if not carefully routed.
✓
Create a separate VPC for each service, with VPC peering only between the API gateway and each service VPC.
Why this is correct
This ensures each service's database is isolated and only accessible via the API.
Use a single VPC with public and private subnets; place databases in private subnets and services in public subnets.
Why it's wrong here
Routing can still allow direct communication between services and databases.
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 for New Solutions — This question tests Design for New Solutions — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Create a separate VPC for each service, with VPC peering only between the API gateway and each service VPC. — Placing services in separate VPCs with VPC peering only for API communication ensures network-level isolation. Option B is correct because it prevents direct database access by not allowing peering between all VPCs. Option A is wrong because a shared VPC with security groups could allow unintended traffic. Option C is wrong because a single VPC with subnets still allows routing between services. Option D is wrong because a transit VPN does not provide the needed isolation.
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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