- A
Configure the web server security group to allow inbound HTTP from 0.0.0.0/0.
Why wrong: Wrong: Exposes web servers to the internet.
- B
Configure the web server security group to allow inbound HTTP from the ALB's security group.
Correct: Only ALB traffic is allowed.
- C
Configure the web server security group to allow inbound HTTP from the ALB's private IP addresses.
Why wrong: Wrong: ALB IPs can change; not scalable.
- D
Configure the web server security group to allow inbound HTTP from the VPC CIDR.
Why wrong: Wrong: Allows any host in the VPC, not just the ALB.
Question 614 of 1,705
Best Practice: Allowing Only ALB Traffic to EC2 Instances
This ANS-C01 practice question tests your understanding of network design. 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 has a VPC with an application load balancer (ALB) in public subnets and web servers in private subnets. The web servers must be accessible only from the ALB. What is the most secure and efficient configuration?
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
✓
Configure the web server security group to allow inbound HTTP from the ALB's security group.
Option B is correct because referencing the ALB's security group in the web server security group rule allows traffic only from the ALB, regardless of its IP addresses. This is the most secure and efficient configuration as it leverages AWS security group referencing, which automatically scales with the ALB's elastic network interfaces and avoids managing IP changes.
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.
- ✗
Configure the web server security group to allow inbound HTTP from 0.0.0.0/0.
Why it's wrong here
Wrong: Exposes web servers to the internet.
- ✓
Configure the web server security group to allow inbound HTTP from the ALB's security group.
Why this is correct
Correct: Only ALB traffic is allowed.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Configure the web server security group to allow inbound HTTP from the ALB's private IP addresses.
Why it's wrong here
Wrong: ALB IPs can change; not scalable.
- ✗
Configure the web server security group to allow inbound HTTP from the VPC CIDR.
Why it's wrong here
Wrong: Allows any host in the VPC, not just the ALB.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The ANS-C01 exam often tests the misconception that using the ALB's private IP addresses is more secure than using security group references, but the trap is that IP-based rules are static and break when the ALB scales, whereas security group references are dynamic and the recommended best practice.
Detailed technical explanation
How to think about this question
When you reference a security group as a source in another security group rule, AWS evaluates the rule based on the private IP addresses of the network interfaces associated with the source security group. This allows the ALB's security group to be used as a logical source, automatically updating as the ALB scales or its IPs change. In a real-world scenario, this is critical for high-traffic applications where ALB nodes are added or removed dynamically, ensuring the web servers remain securely accessible without manual intervention.
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 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.
Visual reference
What to study next
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FAQ
Questions learners often ask
What does this ANS-C01 question test?
Network Design — This question tests Network Design — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Configure the web server security group to allow inbound HTTP from the ALB's security group. — Option B is correct because referencing the ALB's security group in the web server security group rule allows traffic only from the ALB, regardless of its IP addresses. This is the most secure and efficient configuration as it leverages AWS security group referencing, which automatically scales with the ALB's elastic network interfaces and avoids managing IP changes.
What should I do if I get this ANS-C01 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: Jul 4, 2026
This ANS-C01 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 ANS-C01 exam.
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