SAA-C03 Design Secure Architectures Practice Question
An architect is designing a secure VPC architecture. Which TWO actions should be taken to ensure the infrastructure is compliant with security best practices regarding network isolation?
⚠ Common exam trap
SAA-C03 often tests the confusion between stateful and stateless firewalls, and the misconception that Security Groups can deny traffic (they cannot).
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Use Network ACLs as a stateless firewall for subnet-level traffic control.
Option B is correct because Network ACLs are stateless, subnet-level firewalls that evaluate inbound and outbound rules independently, providing an additional layer of traffic control for network isolation in a VPC. Option D is correct because Security Groups are stateful, instance-level firewalls that automatically allow return traffic for permitted connections, which is a fundamental AWS best practice for controlling access to EC2 instances. Option A is incorrect because placing all EC2 instances in a public subnet exposes them directly to the internet and violates network isolation best practices; instances that don't need public access should reside in private subnets. Option C is incorrect because allowing all traffic from 0.0.0.0/0 on all ports effectively disables firewall protection and is a severe security misconfiguration. Option E is incorrect because disabling VPC Flow Logs removes valuable network traffic visibility needed for monitoring, auditing, and incident response, and cost reduction should not come at the expense of security observability.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Place all EC2 instances in the public subnet to maximize accessibility.
Why it's wrong here
Placing all instances in a public subnet exposes them directly to the internet, increasing the attack surface. Security best practices dictate that only necessary resources, like load balancers, should be public, while application and database tiers should reside in private subnets to isolate them from direct inbound traffic.
- ✓
Use Network ACLs as a stateless firewall for subnet-level traffic control.
Why this is correct
Network ACLs act as a first line of defense at the subnet level. Because they are stateless, they require explicit rules for both inbound and outbound traffic, providing a robust way to block or allow traffic ranges before it ever reaches the individual EC2 instances residing within the subnet.
- ✗
Configure Security Groups to allow all traffic (0.0.0.0/0) on all ports.
Why it's wrong here
Allowing all traffic on all ports is a severe security risk that violates the principle of least privilege. Security groups should be configured with specific protocols and port ranges only for authorized traffic sources, ensuring that services are not exposed to unnecessary threats or unauthorized connections from the internet.
- ✓
Implement Security Groups as stateful firewalls for instance-level traffic control.
Why this is correct
Security groups are stateful, meaning if a request is allowed in, the response is automatically allowed out. They are essential for controlling traffic to specific instances, allowing architects to define granular rules that limit communication only to trusted sources, which is fundamental to securing modern cloud-based application architectures.
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Disable VPC Flow Logs to reduce the storage costs in S3.
Why it's wrong here
VPC Flow Logs are critical for security auditing and forensic analysis. Disabling them saves costs but obscures visibility into network traffic patterns. Best practices require keeping these logs enabled to monitor for anomalous traffic, troubleshoot security issues, and maintain a historical record of network activity for compliance and security reviews.
Visual reference
About these practice questions
This SAA-C03 question is part of Courseiva's 149-question bank — original exam-style content with full explanations and wrong-answer analysis, never real exam questions or exam dumps. Learn why practice questions differ from exam dumps →
JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Amazon Web Services exam blueprint
This SAA-C03 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 SAA-C03 exam.