PCDOE Implementing service monitoring strategies Practice Question
A company is running a stateful workload on Compute Engine and has configured a TCP health check on port 8080. The health check is failing, but the application is running and responding on port 8080 when tested manually from within the instance. What is the most likely cause of the health check failure?
⚠ Common exam trap
Google Cloud often tests the misconception that health check failures are always due to application misconfiguration or port mismatches, but the trap here is that the health check probes come from external Google IP ranges that must be explicitly allowed in firewall rules, not from within the instance's own network.
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 firewall rules are not allowing traffic from the health check probe IP ranges.
The health check probes originate from Google's health check systems, which use specific IP ranges (e.g., 35.191.0.0/16, 130.211.0.0/22). If firewall rules on the instance or VPC do not explicitly allow inbound traffic from these probe IP ranges on port 8080, the health check will fail even though the application is running and responding to manual tests from within the instance. This is the most common cause of health check failures when the application itself is healthy.
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 health check is configured to use port 80 instead of port 8080.
Why it's wrong here
The question says port 8080 is configured.
- ✓
The firewall rules are not allowing traffic from the health check probe IP ranges.
Why this is correct
Health check probes use specific IP ranges that must be allowed.
- ✗
The instance's DNS resolution is failing, causing the health check to use the wrong IP.
Why it's wrong here
Health checks use the internal IP, not DNS.
- ✗
The health check response timeout is set too low (e.g., 1 second).
Why it's wrong here
Default timeout is 5 seconds, usually enough.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PCDOE practice question is part of Courseiva's free Google Cloud 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 PCDOE exam.