mediumMultiple Choice
CV0-004 Practice Question: Refer to the exhibit
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?
⚠ Common exam trap
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).
Answer choices
Why each option matters
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.
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 certificate causes TLS handshake failures and browser warnings before any HTTP response, so clients never see 502. Certificate errors fit HTTPS listener misconfiguration; 502 instead indicates the load balancer reached a backend that returned an unparseable or empty response.
- ✗
The security group allows inbound traffic from the load balancer.
Why it's wrong here
Permitting inbound traffic from the load balancer is required for healthy backends and cannot itself cause 502; blocking it would yield timeouts. Security group rules are the culprit when connections are refused, whereas 502 means the backend responded invalidly or the health check failed.
- ✗
The DNS record points to the wrong IP.
Why it's wrong here
A wrong DNS target produces connection timeouts or 404s, not 502, because the load balancer never reaches a backend to receive a malformed response. It would be the cause when clients cannot resolve or connect at all, rather than the gateway receiving an invalid upstream reply.
- ✓
The backend web servers are not responding correctly.
Why this is correct
A 502 Bad Gateway means the load balancer received an invalid or incomplete response from an upstream backend. Since the balancer itself and client connectivity are functioning, the fault lies with the backend web servers failing to respond correctly, matching this option.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This CV0-004 practice question is part of Courseiva's free CompTIA 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 CV0-004 exam.