Google PCA Manage and provision cloud infrastructure Practice Question
This PCA practice question tests your understanding of manage and provision cloud infrastructure. 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.
A company runs a web application on Compute Engine with an HTTP Load Balancer. Users report intermittent 502 Bad Gateway errors. 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.
Why wrong: Quota exceeded would prevent creation or scaling, not cause 502 on existing traffic.
B
Firewall rules block health checks.
Why wrong: Blocked health checks would cause the load balancer to consider instances unhealthy, but 502 occurs only when traffic is actually sent to a failing backend.
C
SSL certificate expired.
Why wrong: Expired SSL causes certificate errors, not 502.
D
Backend instances are unhealthy or overloaded.
502 Bad Gateway typically means the backend is not responding properly.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Backend instances are unhealthy or overloaded.
The 502 Bad Gateway error from an HTTPLoad Balancer typically indicates that the backend instances are failing to respond to the load balancer's health checks or are overwhelmed, causing the load balancer to consider them unhealthy and return a 502 error. This is the most common cause because the load balancer relies on healthy backends to forward traffic, and overloaded or failing instances cannot handle requests.
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.
✗
Load balancer quota exceeded.
Why it's wrong here
Quota exceeded would prevent creation or scaling, not cause 502 on existing traffic.
✗
Firewall rules block health checks.
Why it's wrong here
Blocked health checks would cause the load balancer to consider instances unhealthy, but 502 occurs only when traffic is actually sent to a failing backend.
502 Bad Gateway typically means the backend is not responding properly.
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
The trap here is that candidates often confuse 502 errors with SSL or quota issues, but the PCA exam specifically tests that 502 errors from an HTTPLoad Balancer are almost always due to backend unavailability or overload, not frontend configuration problems.
Detailed technical explanation
How to think about this question
Under the hood, Google Cloud HTTP Load Balancers perform health checks via HTTP GET requests to a configured path (e.g., /healthz) on the backend instances. If the backend is overloaded, it may fail to respond within the timeout (default 5 seconds) or return a non-200 status, causing the load balancer to drain connections and return 502 errors. In a real-world scenario, a sudden traffic spike can overwhelm backend instances, leading to intermittent 502 errors even if health checks pass initially, because the load balancer's connection pool may time out waiting for a 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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PCA question in full detail.
Manage and provision cloud infrastructure — This question tests Manage and provision cloud infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Backend instances are unhealthy or overloaded. — The 502 Bad Gateway error from an HTTP Load Balancer typically indicates that the backend instances are failing to respond to the load balancer's health checks or are overwhelmed, causing the load balancer to consider them unhealthy and return a 502 error. This is the most common cause because the load balancer relies on healthy backends to forward traffic, and overloaded or failing instances cannot handle requests.
What should I do if I get this PCA 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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