The answer is that the web server service is not running or crashed. This is the most likely cause because the EC2 instance passes both status checks and is healthy, SSH access works perfectly, and security groups and network ACLs are correctly configured for port 443, yet the web server remains unreachable. With CPU utilization at only 5%, the instance is not resource-constrained, so the issue must be at the application layer rather than the network or OS stack. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this scenario tests your ability to isolate failures by process of elimination—many candidates mistakenly blame security groups or route tables when connectivity fails, but if SSH works and the instance is healthy, the problem is almost always the service itself. A common trap is overlooking that a stopped web server will still show a healthy instance in CloudWatch. Memory tip: “Healthy instance, SSH fine, port 443 offline? Check the service, not the network.”
SOA-C02 Monitoring, Logging, and Remediation Practice Question
This SOA-C02 practice question tests your understanding of monitoring, logging, and remediation. 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 SysOps administrator is troubleshooting an issue where an EC2 instance running a web server is unreachable. The instance passes status checks and is in a healthy state. Security groups and network ACLs are configured correctly. CloudWatch metrics show CPU utilization is 5%. The administrator can SSH into the instance but cannot connect to the web server on port 443. What is the most likely cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The web server service is not running or crashed.
The instance passes both status checks and is healthy, and the administrator can SSH into it, confirming that the operating system and network stack are functional. Since the web server is unreachable on port 443 despite correct security group and network ACL configurations, and CPU utilization is low (5%), the most likely cause is that the web server service (e.g., Apache, Nginx) has stopped or crashed. This would prevent the instance from listening on port 443, even though the underlying infrastructure is sound.
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.
✗
The security group inbound rule for HTTPS is misconfigured.
Why it's wrong here
Security groups are correctly configured per the scenario.
✗
The instance has an incorrect route table entry.
Why it's wrong here
SSH connectivity shows network routing works for at least one port; the issue is specific to port 443.
✓
The web server service is not running or crashed.
Why this is correct
The application may have failed to start after boot or crashed, which would not be detected by EC2 status checks.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
The instance has insufficient CPU credits.
Why it's wrong here
CPU utilization is 5%, so there are no resource constraints.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often assume a reachability issue must be a network configuration problem (security group or route table), but the combination of successful SSH and failed HTTPS on a low-CPU, healthy instance points directly to the application service not running.
Trap categories for this question
Command / output trap
SSH connectivity shows network routing works for at least one port; the issue is specific to port 443.
Scenario analysis trap
Security groups are correctly configured per the scenario.
Detailed technical explanation
How to think about this question
When a web server service crashes, the OS kernel stops listening on the associated TCP port (443), so even if the security group allows traffic, the SYN packet will be met with a TCP RST or no response. This can be verified by running `ss -tlnp | grep :443` or `netstat -tulpn | grep 443` from within the instance to confirm the service is not bound to the port. In contrast, network-level misconfigurations (security groups, route tables) would typically affect all traffic or be visible via connectivity tests like `telnet` or `nc` from within the VPC.
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.
Monitoring, Logging, and Remediation — This question tests Monitoring, Logging, and Remediation — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The web server service is not running or crashed. — The instance passes both status checks and is healthy, and the administrator can SSH into it, confirming that the operating system and network stack are functional. Since the web server is unreachable on port 443 despite correct security group and network ACL configurations, and CPU utilization is low (5%), the most likely cause is that the web server service (e.g., Apache, Nginx) has stopped or crashed. This would prevent the instance from listening on port 443, even though the underlying infrastructure is sound.
What should I do if I get this SOA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Question Discussion
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