Cloud Spanner Backup Permissions — Instance-Level IAM | Google PCDE Explained
This PCDE practice question tests your understanding of plan and manage database infrastructure. 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 spanner instances list
NAME CONFIG NODES STATE
orders-db regional-us-central1 3 READY
analytics-db regional-us-central1 5 READY
$ gcloud spanner databases list --instance=orders-db
NAME STATE
orders READY
$ gcloud spanner databases get-iam-policy orders --instance=orders-db
bindings:
- members:
- serviceAccount:sa-backup@project.iam.gserviceaccount.com
role: roles/spanner.databaseReader
- members:
- serviceAccount:sa-backup@project.iam.gserviceaccount.com
role: roles/spanner.databaseBackupAdmin
etag: BwXZ...==
```
A company uses Cloud Spanner. The backup service account 'sa-backup' needs to create and manage backups of the 'orders' database. However, backup creation fails with a permission error. What is the most likely 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.
Exhibit
Refer to the exhibit.
```
$ gcloud spanner instances list
NAME CONFIG NODES STATE
orders-db regional-us-central1 3 READY
analytics-db regional-us-central1 5 READY
$ gcloud spanner databases list --instance=orders-db
NAME STATE
orders READY
$ gcloud spanner databases get-iam-policy orders --instance=orders-db
bindings:
- members:
- serviceAccount:sa-backup@project.iam.gserviceaccount.com
role: roles/spanner.databaseReader
- members:
- serviceAccount:sa-backup@project.iam.gserviceaccount.com
role: roles/spanner.databaseBackupAdmin
etag: BwXZ...==
```
A
The service account lacks the spanner.databases.read permission.
Why wrong: The service account has databaseReader role, which includes read access.
B
The service account is assigned the role roles/spanner.databaseBackupAdmin, which is a custom role that does not include the spanner.backups.create permission.
Why wrong: roles/spanner.databaseBackupAdmin is not a predefined role; the correct role is roles/spanner.backupAdmin at the instance level.
C
The backup role must be granted at the instance level, not on the database.
The role roles/spanner.backupAdmin must be granted on the instance, not the database, to create backups.
D
The instance 'orders-db' is in a regional configuration, which does not support backups.
Why wrong: Regional instances support backups; the configuration is not the issue.
The correct answer is that the backup role must be granted at the instance level, not on the database. This is because Cloud Spanner backup IAM permissions, specifically the `spanner.backups.create` permission, are evaluated against the instance resource, not the database resource. Even if you assign `roles/spanner.databaseBackupAdmin` directly to the database, it does not grant the instance-level authority required to initiate and manage backup operations, which is why the service account 'sa-backup' fails. On the Google Professional Cloud Database Engineer exam, this is a classic trap: candidates often assume database-level roles cover all related actions, but Spanner enforces a strict resource hierarchy where backup permissions are an instance-level concern. A reliable memory tip is "Backups belong to the instance, not the database"—think of the instance as the container that owns the backup lifecycle, so permissions must be placed on that container.
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 backup role must be granted at the instance level, not on the database.
Option C is correct because Cloud Spanner backup permissions must be granted at the instance level, not on the database itself. The service account 'sa-backup' needs the `spanner.backups.create` permission on the instance resource to create backups, and assigning a role like `roles/spanner.databaseBackupAdmin` at the database level does not propagate the necessary instance-level permissions, causing the backup creation to fail with a permission error.
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 service account lacks the spanner.databases.read permission.
Why it's wrong here
The service account has databaseReader role, which includes read access.
✗
The service account is assigned the role roles/spanner.databaseBackupAdmin, which is a custom role that does not include the spanner.backups.create permission.
Why it's wrong here
roles/spanner.databaseBackupAdmin is not a predefined role; the correct role is roles/spanner.backupAdmin at the instance level.
✓
The backup role must be granted at the instance level, not on the database.
Why this is correct
The role roles/spanner.backupAdmin must be granted on the instance, not the database, to create backups.
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 'orders-db' is in a regional configuration, which does not support backups.
Why it's wrong here
Regional instances support backups; the configuration is not the issue.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The pitfall is that roles/spanner.databaseBackupAdmin is a predefined role at the database level, but creating backups requires the spanner.backups.create permission at the instance level. Assigning this role at the database level mistakenly gives the impression that backup operations are allowed, but they fail because the instance-level permission is missing.
Detailed technical explanation
How to think about this question
In Cloud Spanner, backups are instance-level resources, not database-level resources, meaning the `spanner.backups.create` permission must be granted on the instance (e.g., via `roles/spanner.backupAdmin` at the instance level) to allow creating backups of any database within that instance. The backup operation also requires the `spanner.databases.get` permission on the source database to read its schema and data, but the core permission for initiating the backup is instance-scoped. This design ensures that backup management is centralized at the instance level, preventing accidental or unauthorized backup creation from database-level roles.
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.
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The backup role must be granted at the instance level, not on the database. — Option C is correct because Cloud Spanner backup permissions must be granted at the instance level, not on the database itself. The service account 'sa-backup' needs the `spanner.backups.create` permission on the instance resource to create backups, and assigning a role like `roles/spanner.databaseBackupAdmin` at the database level does not propagate the necessary instance-level permissions, causing the backup creation to fail with a permission error.
What should I do if I get this PCDE 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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