The answer is that the Cloud Build trigger source archive is stale on push because the archive stored in Cloud Storage is not being updated when new code is pushed to the repository. This failure occurs because the trigger is configured to fetch a static source archive from a specific Cloud Storage bucket, rather than pulling the source directly from the repository. When a developer pushes code to main, the trigger attempts to retrieve the archive from that fixed location, but since no process—such as a Cloud Function or separate upload—rebuilds and replaces the archive on each push, the build either fetches an outdated version or fails entirely if the object no longer exists. On the Google Professional Machine Learning Engineer exam, this scenario tests your understanding of how Cloud Build triggers resolve source code, specifically the distinction between repository-linked triggers and storage-backed archives. A common trap is to misdiagnose this as a permissions or config file issue, but the core problem is the stale archive itself. Memory tip: if the source is in Cloud Storage, a push won’t refresh it—think “archive, not live.”
PMLE Automating and orchestrating ML pipelines Practice Question
This PMLE practice question tests your understanding of automating and orchestrating ml 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.
Exhibit
Refer to the exhibit.
```
symptom: Cloud Build trigger fails with: Build failed: could not resolve source: fetching source: fetching storage object: object not found
trigger configuration:
event: push to branch main
repository: my-repo
included files: 'train/**'
excluded files: 'test/**'
source: gs://my-bucket/source.tar.gz
```
A developer creates a Cloud Build trigger that runs a training pipeline whenever code is pushed to the main branch of the repository. The trigger is configured to use a source archive stored in Cloud Storage. After pushing code to main, the build fails with the error shown. What is the most likely cause of this failure?
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.
Refer to the exhibit.
```
symptom: Cloud Build trigger fails with: Build failed: could not resolve source: fetching source: fetching storage object: object not found
trigger configuration:
event: push to branch main
repository: my-repo
included files: 'train/**'
excluded files: 'test/**'
source: gs://my-bucket/source.tar.gz
```
A
The build configuration file is missing from the source archive.
Why wrong: The error occurs during source fetching, before the build configuration is read.
B
The included files filter 'train/**' excludes all files outside the train directory, causing the build to have no source.
Why wrong: The included files filter controls which files trigger the build, not the source content.
C
The source archive is not being updated when code is pushed, so the trigger tries to fetch an old or nonexistent object.
The trigger points to a static archive; pushing new code does not update the archive, leading to missing source.
D
The service account does not have storage.objectViewer permission on the bucket.
Why wrong: The error message says 'object not found', not permission denied.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The source archive is not being updated when code is pushed, so the trigger tries to fetch an old or nonexistent object.
Option C is correct because the trigger is configured to use a source archive stored in Cloud Storage. When code is pushed to the main branch, the trigger attempts to fetch the archive from the specified Cloud Storage location. If the archive is not updated (e.g., via a separate upload or a Cloud Function that rebuilds the archive on push), the trigger will either fetch an old version or fail if the object does not exist. The error indicates that the build cannot proceed because the source archive is stale or missing, not because of a missing config file or permission issue.
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 build configuration file is missing from the source archive.
Why it's wrong here
The error occurs during source fetching, before the build configuration is read.
✗
The included files filter 'train/**' excludes all files outside the train directory, causing the build to have no source.
Why it's wrong here
The included files filter controls which files trigger the build, not the source content.
✓
The source archive is not being updated when code is pushed, so the trigger tries to fetch an old or nonexistent object.
Why this is correct
The trigger points to a static archive; pushing new code does not update the archive, leading to missing source.
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 service account does not have storage.objectViewer permission on the bucket.
Why it's wrong here
The error message says 'object not found', not permission denied.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume the included files filter (Option B) causes the failure, but the error is about the source archive itself being outdated or missing, not about which files are included within it.
Detailed technical explanation
How to think about this question
Cloud Build triggers can use Cloud Storage as a source by specifying a gs:// URL for the archive. The trigger does not automatically re-upload the archive on each push; it simply references a static object. To keep the archive current, developers must implement a separate process (e.g., a Cloud Function triggered by Cloud Pub/Sub on push events) to rebuild and upload the archive. This is a common pitfall when migrating from repository-based triggers to storage-based triggers, as the latter lack native integration with Git events.
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 media company stores terabytes of video archives that are accessed once a year for audit purposes. Moving these objects to a cold storage tier (Azure Archive, S3 Glacier, or Google Nearline) costs a fraction of hot storage. Questions like this test whether you understand storage tiers, access frequency tradeoffs, and retrieval latency requirements.
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.
Automating and orchestrating ML pipelines — This question tests Automating and orchestrating ML pipelines — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The source archive is not being updated when code is pushed, so the trigger tries to fetch an old or nonexistent object. — Option C is correct because the trigger is configured to use a source archive stored in Cloud Storage. When code is pushed to the main branch, the trigger attempts to fetch the archive from the specified Cloud Storage location. If the archive is not updated (e.g., via a separate upload or a Cloud Function that rebuilds the archive on push), the trigger will either fetch an old version or fail if the object does not exist. The error indicates that the build cannot proceed because the source archive is stale or missing, not because of a missing config file or permission issue.
What should I do if I get this PMLE 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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