The answer is to deploy the backend service in a private subnet and configure its security group to allow inbound traffic only from the frontend service’s security group. This approach leverages security group referencing, which enables traffic between ECS Fargate tasks within the same VPC without exposing the backend to the internet, as tasks in private subnets receive no public IP addresses. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your understanding of network isolation patterns for microservices, often paired with a distractor suggesting an Application Load Balancer or a public subnet for the backend. A common trap is assuming a NAT Gateway is needed for frontend-to-backend communication, but NAT only handles outbound traffic; for secure ECS frontend-backend communication, security group chaining is the key. Memory tip: think “private subnet, private SG—backends stay hidden, frontends stay connected.”
DOP-C02 Resilient Cloud Solutions Practice Question
This DOP-C02 practice question tests your understanding of resilient cloud 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 deploying a web application on Amazon ECS with Fargate. The application consists of a frontend service and a backend service. The DevOps team needs to ensure that the frontend service can communicate with the backend service securely without exposing the backend to the internet. Which THREE steps should the team take? (Choose THREE.)
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Deploy the backend service in a private subnet with no internet access.
Option A is correct because deploying the backend service in a private subnet with no internet access ensures that the backend is not reachable from the internet, which is a fundamental security requirement. In Amazon ECS with Fargate, tasks in a private subnet use an elastic network interface (ENI) with no public IP address, and outbound traffic can be routed through a NATgateway if needed, but inbound traffic from the internet is blocked. This isolates the backend from direct external exposure while still allowing communication from the frontend service within the same VPC.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✓
Deploy the backend service in a private subnet with no internet access.
Why this is correct
Keeps the backend isolated.
Related concept
Read the scenario before looking for a memorised answer.
✓
Use AWS Cloud Map service discovery for the backend service.
Why this is correct
Provides DNS-based service discovery within the VPC.
Related concept
Read the scenario before looking for a memorised answer.
✓
Configure a security group for the backend service that allows inbound traffic only from the frontend service's security group.
Why this is correct
Restricts access to only frontend.
Related concept
Read the scenario before looking for a memorised answer.
✗
Deploy the backend service in a public subnet with an internet-facing Application Load Balancer.
Why it's wrong here
Exposes the backend to the internet.
✗
Use an internet-facing Network Load Balancer for the backend service.
Why it's wrong here
Exposes the backend to the internet.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates might think a load balancer is required for service-to-service communication in ECS, but AWS Cloud Map service discovery combined with security group rules can achieve secure, direct communication without exposing the backend to the internet.
Detailed technical explanation
How to think about this question
Under the hood, Amazon ECS with Fargate assigns each task an ENI in the specified subnet, and security groups act as a virtual firewall at the ENI level. When using AWS Cloud Map service discovery, the frontend service can resolve the backend service's private DNS name (e.g., backend.local) via the AWS-provided Route 53 private hosted zone, enabling secure communication without needing a load balancer. In a real-world scenario, this pattern is common for microservices architectures where inter-service communication must remain within the VPC, and security group rules referencing other security groups (e.g., allowing inbound traffic from the frontend's security group) provide granular, stateful filtering without needing to manage IP addresses.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
TExam Day Tips
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Resilient Cloud Solutions — This question tests Resilient Cloud Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Deploy the backend service in a private subnet with no internet access. — Option A is correct because deploying the backend service in a private subnet with no internet access ensures that the backend is not reachable from the internet, which is a fundamental security requirement. In Amazon ECS with Fargate, tasks in a private subnet use an elastic network interface (ENI) with no public IP address, and outbound traffic can be routed through a NAT gateway if needed, but inbound traffic from the internet is blocked. This isolates the backend from direct external exposure while still allowing communication from the frontend service within the same VPC.
What should I do if I get this DOP-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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