The answer is that failing readiness probes cause the service endpoints to be removed, leading to connection refused errors. This occurs because Kubernetes relies on a successful readiness probe to determine if a pod is ready to accept traffic; when the probe fails, the pod’s IP is immediately removed from the ClusterIP service’s endpoint list. If all pods for a given service fail their probes simultaneously, the service has zero healthy backends, so any request to its ClusterIP is met with a TCP reset or connection refused, as no process is listening on the target port. On the Google Professional Cloud Architect exam, this scenario tests your understanding of how liveness versus readiness probes affect service discovery and traffic routing—a common trap is confusing readiness probes with liveness probes, which only restart unhealthy containers without affecting endpoint membership. Remember the mnemonic: “Readiness removes routes; liveness restarts pods.”
Google PCA Manage implementation of cloud architecture Practice Question
This PCA practice question tests your understanding of manage implementation of cloud architecture. 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.
Your team has deployed a microservices application on Google Kubernetes Engine (GKE) with multiple services communicating via internal ClusterIP services. You notice that some requests between services are failing intermittently with 'connection refused' errors. The services are defined with readiness probes. 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.
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 not passing, causing the service endpoints to be removed.
The 'connection refused' error indicates that the client is attempting to connect to a port on which no process is listening. In GKE, when a readiness probe fails, Kubernetes removes the pod's IP from the corresponding ClusterIP service's endpoints. If all pods for a service fail their readiness probes, the service has no healthy endpoints, and any request to the ClusterIP will be refused because there is no backend to accept the connection. This matches the intermittent nature of the issue, as pods may temporarily fail the probe and then recover.
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 readiness probes are not passing, causing the service endpoints to be removed.
Why this is correct
Failing readiness probes cause the pod to be removed from service endpoints, leading to connection refused.
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 services are not exposed via a VPC peering connection to the client's VPC.
Why it's wrong here
ClusterIP services are internal to the cluster and do not require VPC peering.
✗
The services are using NodePort instead of LoadBalancer type, causing port conflicts.
Why it's wrong here
NodePort works but is not the cause of connection refused; it's a valid type for internal access.
✗
The services are not associated with an Ingress resource.
Why it's wrong here
Ingress is for external HTTP(S) traffic; internal services don't need it.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between readiness and liveness probes, where candidates may incorrectly assume that a failing liveness probe (which restarts the pod) is the cause of 'connection refused', but the key is that readiness probes control endpoint membership, directly causing the error when all endpoints are removed.
Detailed technical explanation
How to think about this question
Kubernetes readiness probes are executed by the kubelet on the node; if the probe fails, the kubelet marks the pod as 'NotReady', and the endpoint controller removes the pod's IP from the Endpoints object associated with the service. The 'connection refused' error occurs at the TCP level because the ClusterIP's iptables rules (or IPVS) forward traffic only to endpoints in the Endpoints list; if the list is empty, the kernel sends a TCP RST, resulting in 'connection refused'. This behavior is distinct from a 'timeout' or 'no route to host', which would indicate network misconfiguration or pod unavailability without a probe failure.
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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this PCA question in full detail.
Manage implementation of cloud architecture — This question tests Manage implementation of cloud architecture — 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 not passing, causing the service endpoints to be removed. — The 'connection refused' error indicates that the client is attempting to connect to a port on which no process is listening. In GKE, when a readiness probe fails, Kubernetes removes the pod's IP from the corresponding ClusterIP service's endpoints. If all pods for a service fail their readiness probes, the service has no healthy endpoints, and any request to the ClusterIP will be refused because there is no backend to accept the connection. This matches the intermittent nature of the issue, as pods may temporarily fail the probe and then recover.
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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