The answer is that the roles/storage.objectCreator role only permits creating new objects, not overwriting existing ones. This is because objectCreator grants the storage.objects.create permission but lacks storage.objects.update, which is required to overwrite a file with the same name. On the Google Professional Cloud Developer exam, this distinction between create and update permissions is a common trap—test takers often assume any write access includes overwriting, but Google Cloud Storage IAM separates these actions deliberately. The objectAdmin or legacyObjectOwner roles include the update permission needed for overwrites, making them suitable for applications that must both read and write files. A useful memory tip: think of objectCreator as “first draft only”—you can add new files, but you cannot revise or replace them.
PCD Practice Question: Designing highly scalable, available, and reliable cloud-native applications
This PCD practice question tests your understanding of designing highly scalable, available, and reliable cloud-native applications. 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 security engineer applied the IAM policy above to a Cloud Storage bucket. The service account "my-sa" is used by an application that needs to read and write files to the bucket. The application reports that it cannot write files. What is the issue?
The policy is missing the "roles/storage.objectAdmin" role.
Why wrong: objectAdmin would allow overwriting, but objectCreator is sufficient for creating new objects. The issue is that the application may be trying to overwrite existing files.
B
The "roles/storage.objectCreator" role only allows creating new objects, but not overwriting existing ones.
objectCreator allows creating new objects but not modifying or overwriting existing objects. To overwrite, the service account needs objectAdmin or objectOwner.
C
The service account lacks permission to list bucket contents.
Why wrong: Listing is not required for writing files; only write (create/overwrite) permissions are needed.
D
The policy has duplicate bindings that cause a conflict.
Why wrong: Duplicate bindings are allowed and do not cause conflicts; the effective permissions are the union of the roles.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The "roles/storage.objectCreator" role only allows creating new objects, but not overwriting existing ones.
The 'roles/storage.objectCreator' role grants permission to create new objects in a Cloud Storage bucket, but it does not allow overwriting existing objects. To overwrite objects, the 'roles/storage.objectAdmin' or 'roles/storage.legacyObjectOwner' role is required, which includes the storage.objects.update permission. Since the application needs to both read and write (including overwrite) files, the objectCreator role is insufficient.
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 policy is missing the "roles/storage.objectAdmin" role.
Why it's wrong here
objectAdmin would allow overwriting, but objectCreator is sufficient for creating new objects. The issue is that the application may be trying to overwrite existing files.
✓
The "roles/storage.objectCreator" role only allows creating new objects, but not overwriting existing ones.
Why this is correct
objectCreator allows creating new objects but not modifying or overwriting existing objects. To overwrite, the service account needs objectAdmin or objectOwner.
Related concept
Read the scenario before looking for a memorised answer.
✗
The service account lacks permission to list bucket contents.
Why it's wrong here
Listing is not required for writing files; only write (create/overwrite) permissions are needed.
✗
The policy has duplicate bindings that cause a conflict.
Why it's wrong here
Duplicate bindings are allowed and do not cause conflicts; the effective permissions are the union of the roles.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between create and update permissions in Cloud Storage IAM roles, trapping candidates who assume that 'write' access includes overwriting existing objects.
Detailed technical explanation
How to think about this question
Cloud Storage IAM roles are composed of granular permissions; 'roles/storage.objectCreator' includes storage.objects.create but not storage.objects.update, which is required to overwrite an existing object. When an application attempts to write to a key that already exists, the API call fails with a 403 Forbidden error because the update permission is missing. This is a common pitfall when using objectCreator for write-heavy workloads that may overwrite files, such as log rotation or data refresh jobs.
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.
Designing highly scalable, available, and reliable cloud-native applications — This question tests Designing highly scalable, available, and reliable cloud-native applications — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The "roles/storage.objectCreator" role only allows creating new objects, but not overwriting existing ones. — The 'roles/storage.objectCreator' role grants permission to create new objects in a Cloud Storage bucket, but it does not allow overwriting existing objects. To overwrite objects, the 'roles/storage.objectAdmin' or 'roles/storage.legacyObjectOwner' role is required, which includes the storage.objects.update permission. Since the application needs to both read and write (including overwrite) files, the objectCreator role is insufficient.
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.
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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