Quick Answer
The answer is VPC Flow Logs, along with Security Groups and Network ACLs, as the three key components for defense in depth in a VPC. Security Groups act as a stateful virtual firewall at the instance level, automatically allowing return traffic for permitted sessions, while Network ACLs provide a stateless, subnet-level barrier that evaluates traffic in both directions independently. VPC Flow Logs capture metadata about IP traffic, enabling you to audit and analyze network behavior for anomalies. On the AWS Certified Security Specialty SCS-C02 exam, this question tests your understanding of layered security controls: Security Groups for host-level protection, NACLs for subnet boundaries, and Flow Logs for visibility. A common trap is confusing stateful Security Groups with stateless NACLs, or forgetting that Flow Logs are a detective control, not a preventive one. Remember the mnemonic “S-N-F” for Security, Network, Flow—each layer covers a different defense depth.
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 security engineer is designing a secure VPC architecture. Which THREE components should be used to implement defense in depth? (Choose three.)
VPN connection
Why wrong: Provides encrypted connectivity, not defense in depth.
Internet gateway
Why wrong: Provides internet access, not security.
Security groups
Instance-level firewall.
Network ACLs
Subnet-level firewall.
VPC Flow Logs
Monitor traffic for analysis.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Security groups
Security groups (C) are stateful virtual firewalls that control inbound and outbound traffic at the instance level. They operate at the network interface (ENI) level, allowing only explicitly permitted traffic and automatically allowing return traffic for permitted sessions. This provides a critical layer of host-level defense within the VPC.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
VPN connection
Why it's wrong here
Provides encrypted connectivity, not defense in depth.
Internet gateway
Why it's wrong here
Provides internet access, not security.
Security groups
Why this is correct
Instance-level firewall.
Related concept
Read the scenario before looking for a memorised answer.
Network ACLs
Why this is correct
Subnet-level firewall.
Related concept
Read the scenario before looking for a memorised answer.
VPC Flow Logs
Why this is correct
Monitor traffic for analysis.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates often confuse connectivity components (VPN, Internet gateway) with security controls, or they overlook that VPC Flow Logs are a detective control (not preventive) but still a valid part of defense in depth, leading them to select A or B instead of the correct trio of security groups, network ACLs, and VPC Flow Logs.
Detailed technical explanation
Security groups support allow rules only (no explicit deny) and are evaluated as a whole; if any rule allows traffic, the traffic is permitted. Network ACLs (D) are stateless and operate at the subnet level, requiring explicit rules for both inbound and outbound traffic, which adds a perimeter defense layer. VPC Flow Logs (E) capture IP traffic metadata (e.g., source/destination IP, ports, protocol, packet/byte counts) and are used for auditing and anomaly detection, not for blocking traffic, but they are essential for monitoring and incident response in a defense-in-depth architecture.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
What to study next
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FAQ
Infrastructure Security — This question tests Infrastructure Security — Read the scenario before looking for a memorised answer..
The correct answer is: Security groups — Security groups (C) are stateful virtual firewalls that control inbound and outbound traffic at the instance level. They operate at the network interface (ENI) level, allowing only explicitly permitted traffic and automatically allowing return traffic for permitted sessions. This provides a critical layer of host-level defense within the VPC.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
This SCS-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the SCS-C02 exam.
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