This CV0-004 practice question tests your understanding of operations and support. 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.
Exhibit
[2025-01-20 14:23:45] ERROR Backend "web-svr-01" health check failed (HTTP 502)
[2025-01-20 14:23:46] ERROR Backend "web-svr-02" health check failed (HTTP 502)
[2025-01-20 14:23:47] ERROR Backend "web-svr-03" health check failed (HTTP 502)
Refer to the exhibit. A cloud load balancer is returning 502 Bad Gateway errors to clients. 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 backend web servers are not responding correctly.
A 502 Bad Gateway error indicates that the load balancer (acting as a proxy or gateway) received an invalid or no response from the upstream backend web servers. This typically occurs when the backend servers are overloaded, have crashed, or are misconfigured (e.g., incorrect health check path, application pool failure). The load balancer successfully forwards the request but fails to get a valid HTTP response, triggering the 502 error.
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 load balancer's SSL certificate is invalid.
Why it's wrong here
An invalid SSL certificate would cause HTTPS errors, not 502 health check failures.
✗
The security group allows inbound traffic from the load balancer.
Why it's wrong here
If security groups were blocking, health checks would fail with a timeout, not 502.
✗
The DNS record points to the wrong IP.
Why it's wrong here
DNS issues would prevent clients from reaching the load balancer, not cause 502 errors from the load balancer.
✓
The backend web servers are not responding correctly.
Why this is correct
502 errors and health check failures indicate the backend servers are not serving correctly.
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between HTTP status codes (502 vs. 504 vs. 503) and their root causes, trapping candidates who confuse a backend response failure (502) with a timeout (504) or an overload condition (503).
Detailed technical explanation
How to think about this question
Under the hood, a 502 error is defined in RFC 7231 Section 6.6.3 as a response from an intermediary (like a reverse proxy or load balancer) when it receives an invalid or no response from the upstream server. In cloud environments (e.g., AWS ALB, Azure Load Balancer), health checks are used to monitor backend instances; if all targets fail health checks, the load balancer will return 502 for any request. A real-world scenario is when a web application's application pool crashes due to memory exhaustion, causing the backend to close the TCP connection prematurely, leaving the load balancer with a partial or empty response.
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 small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
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.
Operations and Support — This question tests Operations and Support — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The backend web servers are not responding correctly. — A 502 Bad Gateway error indicates that the load balancer (acting as a proxy or gateway) received an invalid or no response from the upstream backend web servers. This typically occurs when the backend servers are overloaded, have crashed, or are misconfigured (e.g., incorrect health check path, application pool failure). The load balancer successfully forwards the request but fails to get a valid HTTP response, triggering the 502 error.
What should I do if I get this CV0-004 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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