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CV0-004 Practice Question: A company deployed a web application on an EC2…
A company deployed a web application on an EC2 instance in a public subnet. The instance passes status checks and has a public IP address. The security group allows HTTP (80) from 0.0.0.0/0. Users report that the website is not accessible. What should the administrator check next?
⚠ Common exam trap
The CV0-004 exam often tests the distinction between stateful security groups and stateless network ACLs, trapping candidates who assume that allowing traffic in the security group is sufficient without checking the subnet-level NACL.
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
✓
The network ACL inbound rules.
The security group allows HTTP (80) from 0.0.0.0/0, so inbound traffic is permitted at the instance level. However, the network ACL (NACL) is a stateless firewall that operates at the subnet level. If the NACL inbound rules do not explicitly allow HTTP traffic from the internet (e.g., port 80 from 0.0.0.0/0), the traffic will be dropped before it reaches the EC2 instance, even though the security group allows it. Since the instance passes status checks and has a public IP, the most likely remaining issue is the NACL.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The network ACL inbound rules.
Why this is correct
Network ACLs are stateless and can block inbound traffic even if the security group allows it.
- ✗
The route table for the subnet.
Why it's wrong here
The route table likely already has a default route to the internet gateway for a public subnet.
- ✗
The instance's operating system firewall.
Why it's wrong here
The OS firewall could block traffic, but it is usually not the first thing to check when security groups and NACLs are in place.
- ✗
The instance's user data script.
Why it's wrong here
User data script only runs at launch and does not affect network connectivity.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CV0-004 practice question is part of Courseiva's free CompTIA 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 CV0-004 exam.