The answer is that the Spinnaker service account lacks the compute.instanceGroups.update permission on the project. This error occurs because during the disable phase of a canary deployment, Spinnaker must update the managed instance group to scale down the old server group, and the service account used to authenticate against Google Cloud APIs requires this specific compute permission. On the Google Professional Cloud DevOps Engineer exam, this scenario tests your understanding of how Spinnaker’s cloud provider integration maps to IAM roles, often disguised as a networking or configuration issue. A common trap is to suspect a firewall rule or a misconfigured pipeline stage, but the error message explicitly names the missing permission. Remember the mnemonic “Canary Disable = Compute Update” to link the deployment phase directly to the required IAM role.
PCDOE Building and implementing CI/CD pipelines Practice Question
This PCDOE practice question tests your understanding of building and implementing ci/cd pipelines. 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 company uses Spinnaker for continuous delivery across multiple GKE clusters. After a recent infrastructure change, the 'Canary' deployment strategy fails during the 'disable' phase of the old version. The error log shows: 'Unable to disable server group: Not authorized to perform compute.instanceGroups.update.' What is the most likely root 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 Spinnaker service account lacks the compute.instanceGroups.update permission on the project.
The error 'Unable to disable server group: Not authorized to perform compute.instanceGroups.update' directly indicates an IAM permissions issue. In Spinnaker, the service account used to interact with GCP must have the compute.instanceGroups.update permission to manage instance groups during the disable phase of a canary deployment. Option C correctly identifies that the Spinnaker service account lacks this specific permission on the project.
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 GKE cluster has reached its maximum node quota.
Why it's wrong here
Quota issues would produce resource exhaustion errors, not authorization.
✗
The Cloud Deploy pipeline is missing the required IAM role for the Spinnaker service account.
Why it's wrong here
The error is from Spinnaker directly, not Cloud Deploy.
✓
The Spinnaker service account lacks the compute.instanceGroups.update permission on the project.
Why this is correct
Correct: Spinnaker uses this permission to disable old server groups.
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 Kayenta canary analysis service is not configured correctly.
Why it's wrong here
Kayenta handles metric analysis, not disabling server groups.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the distinction between permissions errors and resource quota errors, leading candidates to incorrectly select quota-related options when the error message explicitly states 'Not authorized'.
Detailed technical explanation
How to think about this question
Spinnaker uses its own service account (or a GCP service account configured in the clouddriver service) to make API calls to GCP. The compute.instanceGroups.update permission is required to modify instance groups, such as resizing them to zero during the 'disable' phase of a canary deployment. This permission is part of the Compute Instance Admin (v1) role (roles/compute.instanceAdmin.v1) or can be granted via a custom role. The error occurs because the service account lacks this specific permission, not because of quota limits or unrelated services like Cloud Deploy or Kayenta.
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.
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.
Building and implementing CI/CD pipelines — This question tests Building and implementing CI/CD pipelines — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The Spinnaker service account lacks the compute.instanceGroups.update permission on the project. — The error 'Unable to disable server group: Not authorized to perform compute.instanceGroups.update' directly indicates an IAM permissions issue. In Spinnaker, the service account used to interact with GCP must have the compute.instanceGroups.update permission to manage instance groups during the disable phase of a canary deployment. Option C correctly identifies that the Spinnaker service account lacks this specific permission on the project.
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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