The answer is the web server on the target instance returning HTTP 502 status codes. This is correct because an ALB health check 502 error cause is almost always the target application itself—the instance’s web server or application layer is responding with a 502 Bad Gateway, indicating it cannot process the request or is misconfigured. On the AWS Certified SysOps Administrator Associate SOA-C02 exam, this question tests your ability to distinguish between network-layer failures (like blocked ports or security groups) and application-layer errors. A common trap is assuming a security group or port issue, but those would produce connection timeouts or resets, not a 502. Remember, the ALB simply relays the target’s response; a 502 means the target is alive but broken at the app level. Memory tip: “502 = App’s fault, not the pipe.”
SOA-C02 Networking and Content Delivery Practice Question
This SOA-C02 practice question tests your understanding of networking and content delivery. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
Network Topology
Refer to the exhibit. The output shows the health status of two targets in a target group. One target is unhealthy with a 502 error. 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 on the target instance is returning HTTP 502 status codes.
Option B is correct because a 502 error from the target indicates that the application on the instance is returning an invalid response or is not functioning correctly, possibly due to an application error. Option A is wrong because if the port were blocked, the health check would fail with a connection timeout or refused, not a 502. Option C is wrong because the security group is stateful and outbound is allowed. Option D is wrong because the ALB health check itself does not cause 502; it's the target's response.
Key principle: NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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 target instance’s security group is blocking the health check traffic.
Why it's wrong here
Security group blocking would cause a timeout or connection refused.
✗
The target instance is not allowing outbound traffic to the ALB.
Why it's wrong here
Outbound traffic is not required for health checks.
✓
The web server on the target instance is returning HTTP 502 status codes.
Why this is correct
502 indicates a bad gateway from the target instance.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Static NAT maps one inside address to one outside address.
✗
The ALB health check is misconfigured with an incorrect path.
Why it's wrong here
Misconfiguration would cause 404 or 503, not 502.
Common exam traps
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Detailed technical explanation
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
Static NAT maps one inside address to one outside address.
PAT allows many inside hosts to share one public address using ports.
Inside local and inside global describe the private and translated addresses.
NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
→Identify inside and outside interfaces first.
→Check whether the scenario needs static NAT, dynamic NAT or PAT.
→Do not confuse NAT matching ACLs with normal packet-filtering intent.
Key takeaway
NAT direction and interface roles matter as much as the IP address mapping. Inside/outside designation controls which traffic is translated.
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.
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SOA-C02 NAT questions on configuration and troubleshooting.
Networking and Content Delivery — This question tests Networking and Content Delivery — Static NAT maps one inside address to one outside address..
What is the correct answer to this question?
The correct answer is: The web server on the target instance is returning HTTP 502 status codes. — Option B is correct because a 502 error from the target indicates that the application on the instance is returning an invalid response or is not functioning correctly, possibly due to an application error. Option A is wrong because if the port were blocked, the health check would fail with a connection timeout or refused, not a 502. Option C is wrong because the security group is stateful and outbound is allowed. Option D is wrong because the ALB health check itself does not cause 502; it's the target's response.
What should I do if I get this SOA-C02 question wrong?
Review the four NAT address types (inside local, inside global, outside local, outside global), PAT port overload, and static vs dynamic NAT use cases. Then practise related SOA-C02 NAT questions on configuration and troubleshooting.
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?
Static NAT maps one inside address to one outside address.
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