Quick Answer
The correct answer is AWS WAF and Security Groups, as they together form the core of a defense-in-depth strategy for a web application on EC2. AWS WAF provides application-layer protection by filtering HTTP requests for common threats like SQL injection and cross-site scripting, while Security Groups act as a stateful virtual firewall at the network layer, controlling inbound and outbound traffic to the EC2 instances. On the AWS Certified Security Specialty SCS-C02 exam, this pairing tests your understanding of layered security, where each service addresses a different OSI model layer—a common trap is confusing Security Groups with NACLs, but remember that Security Groups are stateful and instance-level, whereas NACLs are stateless and subnet-level. GuardDuty and Shield Advanced are detection and DDoS mitigation services, not firewalls, so they don’t fit the prevention requirement. Memory tip: think “WAF for the app, SG for the net” to keep the layers straight.
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 wants to implement a defense-in-depth strategy for its web application running on EC2 instances. Which TWO AWS services should be used to provide both network and application-layer protection?
Amazon GuardDuty
Why wrong: GuardDuty is a threat detection service, not a firewall.
AWS WAF
WAF provides application-layer protection.
Security Groups
Security Groups provide stateful network-layer firewall.
AWS Shield Advanced
Why wrong: Shield Advanced provides DDoS protection, not application-layer filtering.
Network ACLs
Why wrong: NACLs provide network-layer filtering but are stateless and less granular.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
AWS WAF
Options B and C are correct. AWS WAF provides application-layer protection (e.g., SQL injection), and Security Groups act as a virtual firewall for network-layer protection. Option A is wrong because NACLs are network-layer but stateless and less granular. Option D is wrong because GuardDuty is a threat detection service, not a prevention firewall. Option E is wrong because Shield Advanced provides DDoS protection but is not a firewall.
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
For each option: why learners choose it and why it is or isn't the right answer here.
Amazon GuardDuty
Why it's wrong here
GuardDuty is a threat detection service, not a firewall.
AWS WAF
Why this is correct
WAF provides application-layer protection.
Related concept
Standard ACLs match source addresses.
Security Groups
Why this is correct
Security Groups provide stateful network-layer firewall.
Related concept
Standard ACLs match source addresses.
AWS Shield Advanced
Why it's wrong here
Shield Advanced provides DDoS protection, not application-layer filtering.
Network ACLs
Why it's wrong here
NACLs provide network-layer filtering but are stateless and less granular.
Common exam traps
ACLs are processed top to bottom. The first matching entry wins, and an implicit deny usually exists at the end.
Detailed technical explanation
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.
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
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
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 SCS-C02 ACL questions on filtering logic and placement.
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FAQ
Infrastructure Security — This question tests Infrastructure Security — Standard ACLs match source addresses..
The correct answer is: AWS WAF — Options B and C are correct. AWS WAF provides application-layer protection (e.g., SQL injection), and Security Groups act as a virtual firewall for network-layer protection. Option A is wrong because NACLs are network-layer but stateless and less granular. Option D is wrong because GuardDuty is a threat detection service, not a prevention firewall. Option E is wrong because Shield Advanced provides DDoS protection but is not a firewall.
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 SCS-C02 ACL questions on filtering logic and placement.
Standard ACLs match source addresses.
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Last reviewed: Jun 20, 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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