The answer is that failing readiness probes are the most likely cause of intermittent 503 errors in a GKE deployment. When a readiness probe fails, Kubernetes immediately removes the pod from the Service’s endpoints, meaning traffic is no longer routed to it. If multiple pods fail their probes in quick succession, the Service can temporarily have zero available endpoints, causing the load balancer to return 503 errors until the pods recover. On the Google Professional Cloud DevOps Engineer exam, this scenario tests your understanding of how Kubernetes health checks—specifically readiness versus liveness probes—affect traffic routing; a common trap is confusing a liveness probe failure (which restarts the pod) with a readiness probe failure (which only removes it from the endpoint pool). To remember: readiness decides if traffic should arrive, liveness decides if the pod should survive.
PCDOE Implementing service monitoring strategies Practice Question
This PCDOE practice question tests your understanding of implementing service monitoring strategies. 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 team is monitoring a production service on Google Kubernetes Engine (GKE) and notices that a deployment is occasionally returning HTTP 503 errors. The team has set up a ServiceMonitor in Prometheus to scrape metrics from the pods. What is the most likely cause of the intermittent 503 errors?
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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The readiness probes are failing, causing the pods to be removed from the service endpoints.
Intermittent HTTP 503 errors in a GKE deployment typically indicate that the service's endpoints are temporarily unavailable. When a readiness probe fails, Kubernetes removes the pod from the Service's endpoints, causing traffic to be routed to remaining healthy pods. If multiple pods fail their readiness probes simultaneously or in quick succession, the Service may have no available endpoints, resulting in 503 errors for incoming 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.
✗
The pods are crashing and restarting frequently.
Why it's wrong here
Restarts would cause 503s but less likely than readiness probe failures.
✗
The Prometheus scrape interval is too long, causing missed metrics.
Why it's wrong here
Prometheus scraping does not affect pod availability.
✓
The readiness probes are failing, causing the pods to be removed from the service endpoints.
Why this is correct
Readiness probe failures remove pods from service endpoints, causing 503s if all replicas fail.
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.
✗
The container resource limits are set too low, causing out-of-memory errors.
Why it's wrong here
OOM errors cause restarts, not directly 503s.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between liveness probes (which restart pods) and readiness probes (which control traffic routing), and candidates mistakenly attribute 503 errors to pod crashes or resource limits rather than the readiness probe's role in endpoint management.
Detailed technical explanation
How to think about this question
Kubernetes readiness probes are implemented via HTTP GET, TCP socket, or exec commands, and their failure triggers the endpoint controller to remove the pod's IP from the Endpoints object backing the Service. In GKE, the kube-proxy or a CNI plugin (e.g., Calico) watches the Endpoints API and updates iptables or IPVS rules accordingly; a transient readiness failure can cause a brief window where traffic is sent to a pod that is not ready, or no pod is available, leading to 503 errors. Real-world scenarios include application startup delays, temporary database connection issues, or high latency that causes the readiness probe to fail for a few seconds, creating a cascade of endpoint removals.
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
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Implementing service monitoring strategies — This question tests Implementing service monitoring strategies — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The readiness probes are failing, causing the pods to be removed from the service endpoints. — Intermittent HTTP 503 errors in a GKE deployment typically indicate that the service's endpoints are temporarily unavailable. When a readiness probe fails, Kubernetes removes the pod from the Service's endpoints, causing traffic to be routed to remaining healthy pods. If multiple pods fail their readiness probes simultaneously or in quick succession, the Service may have no available endpoints, resulting in 503 errors for incoming requests.
What should I do if I get this PCDOE 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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