- A
Web security group: inbound rule allowing 0.0.0.0/0 on port 443. Database security group: inbound rule allowing the web security group as source on port 3306.
This is correct. The web SG allows internet traffic on port 443, and the database SG uses the web SG as a source, which permits only traffic from instances associated with the web SG on port 3306.
- B
Web security group: inbound rule allowing 0.0.0.0/0 on port 443. Database security group: inbound rule allowing 0.0.0.0/0 on port 3306.
Why wrong: This is incorrect because opening the database SG to the entire internet (0.0.0.0/0) on port 3306 exposes the database to potential attacks from any source, violating security best practices.
- C
Web security group: inbound rule allowing the web security group as source on port 443. Database security group: inbound rule allowing the web security group as source on port 3306.
Why wrong: This is incorrect because the web SG allows inbound traffic from itself (self-reference) on port 443, which does not allow internet traffic. Internet users cannot reach the web tier, so the application would be inaccessible.
- D
Web security group: inbound rule allowing 0.0.0.0/0 on port 443. Database security group: inbound rule allowing the internet-facing Application Load Balancer security group as source on port 3306.
Why wrong: This is incorrect because the scenario does not mention an Application Load Balancer (ALB). Even if an ALB were present, the requirement is for direct communication between the web tier EC2 instances and the database tier, not through a load balancer.
Quick Answer
The correct answer is to configure the web security group with an inbound rule allowing 0.0.0.0/0 on port 443, and the database security group with an inbound rule that references the web security group as the source on port 3306. This works because security group rules are stateful and allow you to use another security group as a source, which dynamically permits traffic only from any EC2 instance associated with that web security group, regardless of its IP address. On the AWS Certified Cloud Practitioner CLF-C02 exam, this scenario tests your understanding of least-privilege access and security group chaining for multi-tier architectures—a common trap is choosing an IP-based rule for the database tier, which would break if instances are replaced or scaled. Remember the key principle: for private tier communication, always prefer security group IDs over CIDR blocks to maintain flexibility and security. A helpful memory tip is “web to world, DB to web only”—the web group opens to the internet, while the DB group locks down to just the web group.
CLF-C02 Security and Compliance Practice Question
This CLF-C02 practice question tests your understanding of security and compliance. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 hosts a multi-tier web application on AWS. The web tier runs on Amazon EC2 instances in a public subnet, and the database tier runs on Amazon EC2 instances in a private subnet. The security team needs to configure security groups to allow only the web tier instances to communicate with the database tier on port 3306 (MySQL). The web tier must be accessible from the internet on port 443. Which security group configuration meets these requirements?
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
Web security group: inbound rule allowing 0.0.0.0/0 on port 443. Database security group: inbound rule allowing the web security group as source on port 3306.
Option A is correct because it uses a security group reference as the source for the database security group's inbound rule on port 3306, which allows traffic only from instances associated with the web security group. The web security group allows inbound HTTPS traffic from the internet (0.0.0.0/0) on port 443, meeting the requirement for public access. This configuration ensures least-privilege access by restricting database communication to only the web tier, without exposing the database to the internet or requiring IP-based rules.
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.
- ✓
Web security group: inbound rule allowing 0.0.0.0/0 on port 443. Database security group: inbound rule allowing the web security group as source on port 3306.
Why this is correct
This is correct. The web SG allows internet traffic on port 443, and the database SG uses the web SG as a source, which permits only traffic from instances associated with the web SG on port 3306.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Web security group: inbound rule allowing 0.0.0.0/0 on port 443. Database security group: inbound rule allowing 0.0.0.0/0 on port 3306.
Why it's wrong here
This is incorrect because opening the database SG to the entire internet (0.0.0.0/0) on port 3306 exposes the database to potential attacks from any source, violating security best practices.
- ✗
Web security group: inbound rule allowing the web security group as source on port 443. Database security group: inbound rule allowing the web security group as source on port 3306.
Why it's wrong here
This is incorrect because the web SG allows inbound traffic from itself (self-reference) on port 443, which does not allow internet traffic. Internet users cannot reach the web tier, so the application would be inaccessible.
- ✗
Web security group: inbound rule allowing 0.0.0.0/0 on port 443. Database security group: inbound rule allowing the internet-facing Application Load Balancer security group as source on port 3306.
Why it's wrong here
This is incorrect because the scenario does not mention an Application Load Balancer (ALB). Even if an ALB were present, the requirement is for direct communication between the web tier EC2 instances and the database tier, not through a load balancer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse security group references with IP-based rules or incorrectly assume that the web security group should reference itself for inbound internet traffic, rather than using 0.0.0.0/0 for public access.
Trap categories for this question
Scenario analysis trap
This is incorrect because the scenario does not mention an Application Load Balancer (ALB). Even if an ALB were present, the requirement is for direct communication between the web tier EC2 instances and the database tier, not through a load balancer.
Detailed technical explanation
How to think about this question
Security groups are stateful and support referencing other security groups as sources, which dynamically resolves to the private IP addresses of all instances associated with the referenced group. This allows the database security group to automatically include any new web instances added to the auto-scaling group without manual IP updates. In contrast, network ACLs are stateless and require explicit inbound and outbound rules, making security groups the preferred choice for instance-level traffic control in multi-tier architectures.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this CLF-C02 question test?
Security and Compliance — This question tests Security and Compliance — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Web security group: inbound rule allowing 0.0.0.0/0 on port 443. Database security group: inbound rule allowing the web security group as source on port 3306. — Option A is correct because it uses a security group reference as the source for the database security group's inbound rule on port 3306, which allows traffic only from instances associated with the web security group. The web security group allows inbound HTTPS traffic from the internet (0.0.0.0/0) on port 443, meeting the requirement for public access. This configuration ensures least-privilege access by restricting database communication to only the web tier, without exposing the database to the internet or requiring IP-based rules.
What should I do if I get this CLF-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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Last reviewed: Jun 11, 2026
This CLF-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 CLF-C02 exam.
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