The answer is to attach a security group to the ECS task with outbound rules allowing only the specific API endpoints. This works because when you run an ECS Fargate task in awsvpc mode, each task receives its own elastic network interface, and security groups can be applied directly to that task-level ENI to control both inbound and outbound container communication. On the AWS Certified Security Specialty SCS-C02 exam, this scenario tests your understanding of the difference between network-layer controls (security groups) and identity-layer controls (IAM policies), with a common trap being to confuse IAM policies for network traffic filtering. Remember that security groups are stateful and act as a virtual firewall at the resource level, making them ideal for per-task isolation, while network ACLs are stateless and operate at the subnet level, unable to differentiate between containers in the same task. Memory tip: “Tasks get tags, but traffic gets security groups” — when securing ECS container communication, always think network interface, not IAM policy.
SCS-C02 Infrastructure Security Practice Question
This SCS-C02 practice question tests your understanding of infrastructure security. 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 runs a containerized application on Amazon ECS with Fargate. The security team wants to ensure that the containers can only communicate with specific external APIs and not with other containers in the same task. Which security control should be applied?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Attach a security group to the ECS task with outbound rules allowing only the specific API endpoints.
Option D is correct because security groups for ECS tasks in awsvpc mode can control inbound/outbound traffic. Option A is wrong because IAM policies control API calls, not network traffic. Option B is wrong because network ACLs are stateless and applied at subnet level, not per task. Option C is wrong because VPC endpoints are for accessing AWS services, not for container communication.
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.
✗
Configure network ACLs on the subnets where the tasks run.
Why it's wrong here
NACLs are stateless and apply to all instances in a subnet, not per container.
✗
Apply an IAM policy to the task execution role to restrict API calls.
Why it's wrong here
IAM policies control permissions to call AWS APIs, not network traffic.
✓
Attach a security group to the ECS task with outbound rules allowing only the specific API endpoints.
Why this is correct
When using awsvpc network mode, tasks get their own security groups that can filter traffic.
Use VPC endpoints to restrict traffic to specific APIs.
Why it's wrong here
VPC endpoints are for private connectivity to AWS services, not for controlling container egress.
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 SCS-C02 subnetting questions on CIDR, address ranges, and subnet selection.
Infrastructure Security — This question tests Infrastructure Security — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: Attach a security group to the ECS task with outbound rules allowing only the specific API endpoints. — Option D is correct because security groups for ECS tasks in awsvpc mode can control inbound/outbound traffic. Option A is wrong because IAM policies control API calls, not network traffic. Option B is wrong because network ACLs are stateless and applied at subnet level, not per task. Option C is wrong because VPC endpoints are for accessing AWS services, not for container communication.
What should I do if I get this SCS-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 SCS-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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