SK0-005 server-administration Practice Question
Exhibit
2025/04/07 09:15:32 [error] 1234#1234: *1 connect() failed (111: Connection refused) while connecting to upstream, client: 192.168.1.50, server: example.com, request: "GET /app HTTP/1.1", upstream: "http://10.0.1.25:8080/", host: "example.com"
Refer to the exhibit. An administrator receives reports that a web application is returning HTTP 502 errors. The administrator examines the Nginx error log on the reverse proxy server and sees the following. Which of the following is MOST likely causing the errors?
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 upstream server at 10.0.1.25:8080 refuses connections.
Option A is correct because the error 'Connection refused' indicates the upstream server (10.0.1.25:8080) is not accepting connections, typically because the backend service is down or the port is closed. Option B is incorrect because if Nginx were not running, no such log entry would be generated. Option C is incorrect because the client's DNS resolution is not involved after Nginx has already attempted to contact the upstream IP. Option D is incorrect because a firewall blocking outbound connections would cause a timeout, not a 'Connection refused' message.
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 Nginx service is not running.
Why it's wrong here
If Nginx were down, it would not log this error; the reverse proxy must be operational to generate the entry.
- ✓
The upstream server at 10.0.1.25:8080 refuses connections.
Why this is correct
'Connection refused' directly signals that the upstream server is not listening on that port or is actively rejecting connections.
- ✗
The firewall on the reverse proxy is blocking port 80.
Why it's wrong here
A firewall block would typically result in a timeout, not an immediate connection refusal from the upstream server.
- ✗
The client's DNS cannot resolve example.com.
Why it's wrong here
The error occurs at the backend connection level, long after client DNS resolution has succeeded.
Visual reference
Go deeper
Related to this question
Key term
Firewall
A firewall is a network security system that monitors and controls incoming and outgoing traffic based on predetermined security rules to protect trusted internal networks from untrusted external networks.
Key term
DNS
DNS is the system that translates human-friendly domain names like example.com into machine-readable IP addresses so computers can find each other on a network.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed July 2026 · checked against the official CompTIA exam blueprint
This SK0-005 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 SK0-005 exam.