The answer is that the cluster was not created with the Istio on GKE add-on enabled, so the proxy logs are not automatically collected. This is because the Istio on GKE add-on configures a dedicated logging pipeline that automatically forwards Istio-proxy sidecar logs to Cloud Logging; without this add-on, the sidecar containers run correctly but their stdout and stderr streams are not routed to the Cloud Logging agent. On the Google Professional Cloud Developer exam, this scenario tests your understanding of how managed Istio on GKE differs from a manual Istio installation—specifically, that automatic log collection is a feature of the add-on, not of the sidecar itself. A common trap is assuming that any running sidecar container will automatically send logs to Cloud Logging, but the add-on is required to bridge the telemetry pipeline. Remember the memory tip: “Add-on for logs, no add-on for fog.”
PCD Managing application performance monitoring Practice Question
This PCD practice question tests your understanding of managing application performance monitoring. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 is running a microservices application on Google Kubernetes Engine (GKE). They have implemented Cloud Monitoring and Cloud Logging, but recently they noticed that the Istio-proxy sidecar logs are missing from Cloud Logging. The application pods are running correctly and the sidecar containers are present. What is the most likely cause of the missing logs?
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 cluster was not created with the Istio on GKE add-on enabled, so proxy logs are not automatically collected.
Option B is correct because when using Istio on GKE, the Istio-proxy sidecar logs are automatically collected and sent to Cloud Logging only if the cluster was created with the 'Istio on GKE' add-on enabled. Without this add-on, the sidecar logs are not automatically forwarded, even though the sidecar containers are present and the application pods are running correctly. The add-on configures the necessary logging pipeline for Istio telemetry and logs.
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 Istio-proxy logs are being sent to Stackdriver but are filtered by a log sink exclusion.
Why it's wrong here
No evidence of a log sink exclusion exists, and logs are not appearing at all.
✓
The cluster was not created with the Istio on GKE add-on enabled, so proxy logs are not automatically collected.
Why this is correct
Istio on GKE add-on enables automatic log collection for sidecar proxies.
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 Cloud Logging agent is not installed on the cluster nodes.
Why it's wrong here
The logging agent is working for application logs, so it is installed.
✗
The sidecar container is not configured to output logs to stdout/stderr.
Why it's wrong here
Istio-proxy by default outputs access logs to stdout.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume all container logs, including sidecar logs, are automatically collected by GKE's default logging, but Cisco tests the specific requirement that Istio-proxy logs require the 'Istio on GKE' add-on to be enabled for automatic forwarding to Cloud Logging.
Trap categories for this question
Command / output trap
Istio-proxy by default outputs access logs to stdout.
Detailed technical explanation
How to think about this question
Under the hood, the 'Istio on GKE' add-on deploys a managed control plane and configures a fluentd-based logging pipeline that specifically captures Envoy proxy logs from sidecar containers and forwards them to Cloud Logging. Without this add-on, the sidecar logs are written to the container's stdout/stderr but are not automatically ingested by the GKE logging integration, which only collects node and container logs from the default logging pipeline. In a real-world scenario, teams often enable the add-on after cluster creation to gain visibility into Istio telemetry without manual fluentd configuration.
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.
Managing application performance monitoring — This question tests Managing application performance monitoring — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The cluster was not created with the Istio on GKE add-on enabled, so proxy logs are not automatically collected. — Option B is correct because when using Istio on GKE, the Istio-proxy sidecar logs are automatically collected and sent to Cloud Logging only if the cluster was created with the 'Istio on GKE' add-on enabled. Without this add-on, the sidecar logs are not automatically forwarded, even though the sidecar containers are present and the application pods are running correctly. The add-on configures the necessary logging pipeline for Istio telemetry and logs.
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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Question Discussion
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