The answer is to place ECS Fargate services in private subnets with a NAT Gateway and the Application Load Balancer in public subnets. This configuration is correct because it ensures that the ALB, which must be internet-facing to receive traffic, resides in public subnets while the Fargate tasks remain isolated in private subnets for security, using the NAT Gateway only for outbound internet access (e.g., pulling container images) without exposing the services directly. On the AWS Certified Solutions Architect Professional SAP-C02 exam, this scenario tests your understanding of VPC networking for microservices, specifically the trade-off between security and operational overhead—a common trap is choosing public subnets for simplicity, which violates least-privilege principles, or selecting an NLB for HTTP traffic, which fails at Layer 7. Remember the mnemonic: “ALB in public, tasks in private, NAT for outbound—secure and serverless.”
SAP-C02 Design for New Solutions Practice Question
This SAP-C02 practice question tests your understanding of design for new solutions. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 ECS with Fargate. Services need to communicate securely within a VPC and be accessible from the internet via an Application Load Balancer. The solution must minimize operational overhead. Which networking configuration should be used?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Services in private subnets with a NAT Gateway and an ALB in public subnets.
Option A is correct because placing services in private subnets with a NATGateway and ALB in public subnets provides secure internal communication and internet access. Option B is wrong because public subnets expose services directly. Option C is wrong because an NLB is for TCP, not HTTP. Option D is wrong because a single public subnet lacks redundancy.
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.
✓
Services in private subnets with a NAT Gateway and an ALB in public subnets.
Why this is correct
Private subnets provide isolation, NAT for outbound, ALB for inbound.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Services in public subnets with Internet Gateways and an ALB.
Why it's wrong here
Public subnets expose services directly, less secure.
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: Services in private subnets with a NAT Gateway and an ALB in public subnets. — Option A is correct because placing services in private subnets with a NAT Gateway and ALB in public subnets provides secure internal communication and internet access. Option B is wrong because public subnets expose services directly. Option C is wrong because an NLB is for TCP, not HTTP. Option D is wrong because a single public subnet lacks redundancy.
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.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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Question Discussion
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