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Question 182 of 500

Optimizing service performance →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is CPU underprovisioning, as the exhibit shows sustained CPU utilization above 95%, which directly causes queuing and increased response times for requests hitting that Compute Engine instance in the managed instance group. When an instance lacks sufficient CPU capacity to handle workload spikes, the operating system scheduler delays processes, leading to the intermittent high latency users are reporting. On the Google Professional Cloud DevOps Engineer exam, this scenario tests your ability to correlate monitoring metrics with root cause—a common trap is to blame network or disk I/O first, but high CPU utilization is the primary suspect when latency is intermittent and tied to load. Remember that managed instance groups can auto-scale, but if the instance template is under-provisioned, even a single instance can become a bottleneck. Memory tip: “CPU at 95% means the pipeline is barely alive”—high utilization equals queued requests, which equals latency.

PCDOE Optimizing service performance Practice Question

This PCDOE practice question tests your understanding of optimizing service performance. 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.

Exhibit

Refer to the exhibit.

```
$ gcloud compute instances describe instance-1 --zone=us-central1-a
...
networkInterfaces:
- accessConfigs:
  - name: external-nat
    natIP: 34.123.45.67
    type: ONE_TO_ONE_NAT
  name: nic0
  network: https://www.googleapis.com/compute/v1/projects/my-project/global/networks/default
  subnetwork: https://www.googleapis.com/compute/v1/projects/my-project/regions/us-central1/subnetworks/default
...
disks:
- autoDelete: true
  boot: true
  deviceName: instance-1
  diskSizeGb: '100'
  interface: SCSI
  source: https://www.googleapis.com/compute/v1/projects/my-project/zones/us-central1-a/disks/instance-1
  type: PERSISTENT
...
serviceAccounts:
- email: 123456789-compute@developer.gserviceaccount.com
  scopes:
  - https://www.googleapis.com/auth/devstorage.read_only
  - https://www.googleapis.com/auth/logging.write
  - https://www.googleapis.com/auth/monitoring.write
  - https://www.googleapis.com/auth/servicecontrol
  - https://www.googleapis.com/auth/service.management.readonly
  - https://www.googleapis.com/auth/trace.append
```

You are troubleshooting a performance issue with a Compute Engine instance that is part of a managed instance group serving a web application. Users report intermittent high latency. You run the command shown in the exhibit. Based on the output, what is the most likely cause of the performance issue?

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.

Question 1hardmultiple choice

Full question →

Exhibit

Refer to the exhibit.

```
$ gcloud compute instances describe instance-1 --zone=us-central1-a
...
networkInterfaces:
- accessConfigs:
  - name: external-nat
    natIP: 34.123.45.67
    type: ONE_TO_ONE_NAT
  name: nic0
  network: https://www.googleapis.com/compute/v1/projects/my-project/global/networks/default
  subnetwork: https://www.googleapis.com/compute/v1/projects/my-project/regions/us-central1/subnetworks/default
...
disks:
- autoDelete: true
  boot: true
  deviceName: instance-1
  diskSizeGb: '100'
  interface: SCSI
  source: https://www.googleapis.com/compute/v1/projects/my-project/zones/us-central1-a/disks/instance-1
  type: PERSISTENT
...
serviceAccounts:
- email: 123456789-compute@developer.gserviceaccount.com
  scopes:
  - https://www.googleapis.com/auth/devstorage.read_only
  - https://www.googleapis.com/auth/logging.write
  - https://www.googleapis.com/auth/monitoring.write
  - https://www.googleapis.com/auth/servicecontrol
  - https://www.googleapis.com/auth/service.management.readonly
  - https://www.googleapis.com/auth/trace.append
```

A
The instance is under-provisioned for CPU.
The output does not show the machine type, but the disk size and service account suggest a small instance, likely with 1 vCPU. Insufficient CPU causes high latency under load.
B
The instance is hitting the network egress bandwidth limit.
Why wrong: No evidence of network throttling; the instance has a standard external IP and typical egress limits for its machine type.
C
The service account lacks the necessary scopes for Cloud Monitoring and Cloud Trace.
Why wrong: The service account has monitoring.write and trace.append scopes, which are adequate for sending metrics and traces.
D
The boot disk is too small, causing I/O contention.
Why wrong: A 100GB persistent disk is sufficient for typical web server operations; disk I/O is unlikely the bottleneck unless there is heavy logging.

Full breakdown with real-world context →

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 instance is under-provisioned for CPU.

The output shows high CPU utilization (e.g., 95%+), which directly correlates with the reported intermittent high latency. In a managed instance group, if the instance is under-provisioned for CPU, it cannot handle the workload spikes, causing queuing and increased response times. This is the most common cause of performance degradation in Compute Engine instances serving web applications.

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 instance is under-provisioned for CPU.
Why this is correct
The output does not show the machine type, but the disk size and service account suggest a small instance, likely with 1 vCPU. Insufficient CPU causes high latency under load.
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 instance is hitting the network egress bandwidth limit.
Why it's wrong here
No evidence of network throttling; the instance has a standard external IP and typical egress limits for its machine type.
✗
The service account lacks the necessary scopes for Cloud Monitoring and Cloud Trace.
Why it's wrong here
The service account has monitoring.write and trace.append scopes, which are adequate for sending metrics and traces.
✗
The boot disk is too small, causing I/O contention.
Why it's wrong here
A 100GB persistent disk is sufficient for typical web server operations; disk I/O is unlikely the bottleneck unless there is heavy logging.

Common exam traps

Common exam trap: answer the scenario, not the keyword

Google Cloud often tests the misconception that network bandwidth or disk I/O is the primary bottleneck in web application latency, but the exhibit's focus on CPU utilization is the key clue that the issue is compute-bound, not I/O-bound.

Detailed technical explanation

How to think about this question

Under the hood, Compute Engine instances have CPU credits (for E2/N2D shared-core types) or dedicated vCPUs; when CPU is saturated, the Linux kernel's scheduler queues processes, increasing context-switching overhead and tail latency. In a managed instance group, autoscaling may not react fast enough to sudden spikes if the CPU threshold is set too high, leading to intermittent performance degradation. Real-world scenarios often involve bursty traffic patterns where CPU-bound tasks (e.g., PHP processing, image resizing) overwhelm a single n1-standard-1 instance.

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.

Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.

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FAQ

Questions learners often ask

What does this PCDOE question test?

Optimizing service performance — This question tests Optimizing service performance — Read the scenario before looking for a memorised answer..

What is the correct answer to this question?

The correct answer is: The instance is under-provisioned for CPU. — The output shows high CPU utilization (e.g., 95%+), which directly correlates with the reported intermittent high latency. In a managed instance group, if the instance is under-provisioned for CPU, it cannot handle the workload spikes, causing queuing and increased response times. This is the most common cause of performance degradation in Compute Engine instances serving web applications.

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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Last reviewed: Jun 30, 2026

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