- A
The load balancer is misconfigured with wrong backend type.
Why wrong: Misconfiguration would likely cause consistent failures.
- B
The backend instances are running out of memory.
Why wrong: Memory exhaustion may cause other errors, not specifically 502.
- C
The SSL certificate has expired.
Why wrong: SSL certificate issues result in TLS errors, not 502.
- D
The connection draining timeout is too short.
Short connection draining timeout causes in-flight requests to be terminated, leading to 502 errors.
Question 696 of 999
Cloud Load Balancer 502 Errors Due to Connection Draining
This PCD practice question tests your understanding of deploying applications. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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.
An application running on Compute Engine instances behind a Cloud Load Balancer experiences intermittent 502 errors. The health checks pass but sometimes requests time out. 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.
Quick Answer
The answer is a connection draining timeout that is too short. This is correct because connection draining allows existing in-flight requests to complete before an instance is removed from the load balancer’s pool; if the timeout is set too low, active requests are abruptly terminated, resulting in 502 errors even when health checks pass successfully. On the Google Professional Cloud Developer exam, this scenario tests your understanding of how Cloud Load Balancer manages instance lifecycle and graceful shutdowns—a common trap is to blame health checks or SSL configuration, but those would cause consistent failures or SSL-specific errors, not intermittent timeouts. The key distinction is that health checks confirm the instance is alive, while connection draining handles the graceful completion of existing traffic. Memory tip: think of “draining” as a slow sink—if you pull the plug too fast (short timeout), water (requests) spills over, causing 502 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 connection draining timeout is too short.
Option D is correct because a connection draining timeout that is too short can cause the load balancer to close connections prematurely while backend instances are still processing requests. This results in intermittent 502 errors and timeouts, even though health checks pass, as the instances are healthy but connections are being terminated before responses are sent.
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 is misconfigured with wrong backend type.
Why it's wrong here
Misconfiguration would likely cause consistent failures.
- ✗
The backend instances are running out of memory.
Why it's wrong here
Memory exhaustion may cause other errors, not specifically 502.
- ✗
The SSL certificate has expired.
Why it's wrong here
SSL certificate issues result in TLS errors, not 502.
- ✓
The connection draining timeout is too short.
Why this is correct
Short connection draining timeout causes in-flight requests to be terminated, leading to 502 errors.
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
A common mistake is to assume that 502 errors always indicate backend health issues, but in Google Cloud Load Balancing, 502 errors often stem from connection draining or timeout settings, not health check failures. Health checks passing does not guarantee that connections are not being terminated prematurely.
Detailed technical explanation
How to think about this question
Connection draining in Google Cloud Load Balancing allows in-flight requests to complete before an instance is removed from service. If the draining timeout (default 300 seconds) is set too low, the load balancer may terminate connections that are still processing, causing 502 errors. This is distinct from health check failures—health checks test liveness at a protocol level (e.g., HTTP GET on a specific path), while connection draining affects existing TCP connections. In real-world scenarios, this often occurs during rolling updates or autoscaling events when instances are deregistered but still handling long-lived requests.
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.
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this PCD question test?
Deploying applications — This question tests Deploying applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The connection draining timeout is too short. — Option D is correct because a connection draining timeout that is too short can cause the load balancer to close connections prematurely while backend instances are still processing requests. This results in intermittent 502 errors and timeouts, even though health checks pass, as the instances are healthy but connections are being terminated before responses are sent.
What should I do if I get this PCD 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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Last reviewed: Jul 4, 2026
This PCD 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 PCD exam.
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