The correct next step is to check the network ACL (NACL) associated with the instance’s subnet. While security groups are stateful and automatically allow return traffic, NACLs are stateless, meaning they evaluate both inbound and outbound rules separately, and a missing outbound allow rule for ephemeral ports (1024–65535) can silently block return traffic even when the security group permits the request. On the AWS Certified Developer Associate DVA-C02 exam, this scenario tests your understanding of the layered defense model: when an EC2 instance is unreachable via its public IP but passes status checks and security group rules appear correct, the common trap is to overlook the subnet-level NACL. Remember that security groups filter at the instance level, while NACLs filter at the subnet boundary—and because NACLs are stateless, you must check both directions. A quick memory tip: “NACL is stateless, so check both in and out; security groups are stateful, so they handle return traffic without a doubt.”
DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. 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 developer notices that an EC2 instance running a web application is unreachable via its public IP. The instance passes status checks but security group rules appear correct. What should the developer check NEXT?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check the network ACL associated with the subnet for rules that may block traffic.
The instance passes status checks and security group rules appear correct, which rules out OS-level and security group issues. Since the instance is unreachable via its public IP, the next logical step is to check the network ACL (NACL) associated with the subnet, because NACLs are stateless and can block inbound or outbound traffic even if security groups allow it. NACLs evaluate rules in order by rule number, and a deny rule (or missing allow rule) for the required ephemeral ports (e.g., 1024-65535 for return traffic) could silently drop packets.
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.
✗
Verify that the instance has an Elastic IP associated.
Why it's wrong here
Instance has a public IP; Elastic IP is not necessary for reachability.
✓
Check the network ACL associated with the subnet for rules that may block traffic.
Why this is correct
NACLs are stateless and can block traffic even if security groups allow it.
Related concept
Read the scenario before looking for a memorised answer.
✗
Review the route table for a route to an internet gateway.
Why it's wrong here
Route table likely correct if instance is reachable at some point.
✗
Inspect the IAM role attached to the instance for network permissions.
Why it's wrong here
IAM roles do not control network traffic.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume security group rules are the only network filter and overlook the stateless nature of network ACLs, which can block traffic even when security groups are correctly configured.
Detailed technical explanation
How to think about this question
Network ACLs are stateless, meaning they evaluate inbound and outbound rules independently; for a web server to respond to a client, the outbound NACL must allow ephemeral ports (typically 1024-65535) for return traffic, even if the inbound NACL allows HTTP/HTTPS. A common misconfiguration is allowing inbound HTTP (port 80) but forgetting to allow outbound ephemeral ports, which causes the server to send responses that are dropped by the NACL. AWS security groups are stateful and automatically allow return traffic, so this issue does not occur with security groups, highlighting why NACL misconfigurations are a frequent troubleshooting pitfall.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Check the network ACL associated with the subnet for rules that may block traffic. — The instance passes status checks and security group rules appear correct, which rules out OS-level and security group issues. Since the instance is unreachable via its public IP, the next logical step is to check the network ACL (NACL) associated with the subnet, because NACLs are stateless and can block inbound or outbound traffic even if security groups allow it. NACLs evaluate rules in order by rule number, and a deny rule (or missing allow rule) for the required ephemeral ports (e.g., 1024-65535 for return traffic) could silently drop packets.
What should I do if I get this DVA-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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This DVA-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 DVA-C02 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.