The correct next step is to check the security group and network ACL rules to ensure inbound traffic is allowed. This is the right action because when an EC2 instance is running, its status checks pass, and the system log shows no errors, the problem is almost certainly a network-layer restriction rather than an OS or hardware failure. Security groups act as a virtual firewall at the instance level, while network ACLs provide stateless filtering at the subnet level, and either can silently drop traffic even when the instance itself is healthy. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this scenario tests your ability to isolate connectivity issues by ruling out lower-layer causes first—a common trap is wasting time rebooting the instance or checking the OS when the real culprit is a misconfigured inbound rule. Remember the mnemonic: “Status checks green, but can’t be seen? Check the SG and NACL between.”
DOP-C02 Incident and Event Response Practice Question
This DOP-C02 practice question tests your understanding of incident and event response. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 DevOps engineer is investigating an incident where an EC2 instance became unreachable. The engineer checks the AWS Management Console and finds the instance is running, but the status check shows '2/2 checks passed' and the system log shows no errors. What should the engineer do NEXT to diagnose the connectivity issue?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Check the security group and network ACL rules to ensure inbound traffic is allowed.
Since the instance is running, status checks pass, and the system log shows no errors, the issue is not with the operating system or underlying hardware. The most likely cause is a network-layer restriction, such as security group or network ACL rules blocking inbound traffic. Checking these rules is the correct next step because they control traffic at the instance and subnet levels, respectively, and misconfigurations here are a common cause of unreachability despite healthy instance status.
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.
✗
Review the CloudWatch metrics for CPU utilization and network throughput.
Why it's wrong here
Metrics may not show the cause of unreachability if instance is healthy.
✗
Reboot the instance to reset the network interface.
Why it's wrong here
Rebooting is unnecessary if the instance is running and healthy.
✗
Stop and start the instance to move it to new underlying hardware.
Why it's wrong here
Stopping/starting is invasive and not first step.
✓
Check the security group and network ACL rules to ensure inbound traffic is allowed.
Why this is correct
Connectivity issues often stem from network permissions.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume a 'running' instance with passing status checks guarantees network reachability, overlooking that security groups and NACLs can silently drop traffic without any error in system logs or status checks.
Trap categories for this question
Command / output trap
Metrics may not show the cause of unreachability if instance is healthy.
Detailed technical explanation
How to think about this question
Security groups act as a virtual firewall at the instance level, evaluating inbound and outbound traffic based on rules; they are stateful, meaning return traffic is automatically allowed. Network ACLs operate at the subnet level and are stateless, requiring explicit rules for both inbound and outbound traffic. In practice, a common misconfiguration is allowing outbound traffic but forgetting to add an inbound rule for the specific protocol (e.g., SSH on TCP port 22), which would cause the instance to appear healthy but be unreachable from external clients.
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 healthcare organisation deploys an application with a public-facing web tier and a private database tier. The database subnet has no public IP and only accepts connections from the web tier's security group. Questions like this test whether you can design cloud network isolation using VNets/VPCs, subnets, and security group rules.
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.
Incident and Event Response — This question tests Incident and Event Response — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Check the security group and network ACL rules to ensure inbound traffic is allowed. — Since the instance is running, status checks pass, and the system log shows no errors, the issue is not with the operating system or underlying hardware. The most likely cause is a network-layer restriction, such as security group or network ACL rules blocking inbound traffic. Checking these rules is the correct next step because they control traffic at the instance and subnet levels, respectively, and misconfigurations here are a common cause of unreachability despite healthy instance status.
What should I do if I get this DOP-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 DOP-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 DOP-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.