The answer is to create a separate VPC for each service and use VPC peering for API communication only. This approach enforces true microservice isolation by placing each service’s database and compute resources into its own network boundary, preventing any direct network-level access between services. VPC peering then acts as a controlled bridge, allowing only the specific API traffic you explicitly route, while all other traffic—including database connections—is blocked by default. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of network segmentation versus security group or IAM-only controls; a common trap is assuming security groups alone suffice, but they cannot prevent a compromised container from reaching another service’s database within the same VPC. Remember the memory tip: “One VPC per service, peer only what’s necessary” to keep isolation strict and attack surfaces minimal.
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. 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 company is building a microservices architecture on Amazon ECS with Fargate. Each service must be isolated and communicate only via APIs. The company needs to enforce that services cannot directly access each other's databases. Which approach should be used?
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 and use VPC peering for API communication only.
Placing each service in its own VPC with VPC peering (Option B) provides network isolation and controlled access. Option A (same VPC) does not isolate databases. Option C (security groups) is less granular. Option D (IAM roles) does not prevent network access.
Key principle: ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
Use a single VPC with network ACLs to block database ports between services.
Why it's wrong here
NACLs are stateless and less dynamic; they can be complex to manage.
✗
Use IAM policies to restrict database access at the API level.
Why it's wrong here
IAM policies control API calls, not direct network access to databases.
✗
Place all services in the same VPC and use security groups to restrict database access.
Why it's wrong here
Security groups can restrict but still allow potential lateral movement if misconfigured.
✓
Create a separate VPC for each service and use VPC peering for API communication only.
Why this is correct
Separate VPCs provide strong isolation; VPC peering allows controlled API traffic.
Related concept
Standard ACLs match source addresses.
Common exam traps
Common exam trap: ACLs stop at the first match
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
How to think about this question
ACL questions test precision: source, destination, protocol, port and direction. A generally correct ACL can still fail if it is applied on the wrong interface or in the wrong direction.
KKey Concepts to Remember
Standard ACLs match source addresses.
Extended ACLs can match source, destination, protocol and ports.
The first matching ACL entry is used.
There is usually an implicit deny at the end.
TExam Day Tips
→Check inbound versus outbound direction.
→Read the ACL from top to bottom.
→Look for a broader permit or deny above the intended line.
Key takeaway
ACLs process entries top to bottom and stop at the first match. Entry order and interface direction matter as much as the permit or deny statement.
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 ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SAP-C02 ACL questions on filtering logic and placement.
Design for New Solutions — This question tests Design for New Solutions — Standard ACLs match source addresses..
What is the correct answer to this question?
The correct answer is: Create a separate VPC for each service and use VPC peering for API communication only. — Placing each service in its own VPC with VPC peering (Option B) provides network isolation and controlled access. Option A (same VPC) does not isolate databases. Option C (security groups) is less granular. Option D (IAM roles) does not prevent network access.
What should I do if I get this SAP-C02 question wrong?
Review ACL processing order, placement rules (standard near destination, extended near source), and inbound vs outbound direction. Study wildcard masks and implicit deny. Then practise related SAP-C02 ACL questions on filtering logic and placement.
What is the key concept behind this question?
Standard ACLs match source addresses.
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Question Discussion
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