Question

Difficulty: HardConfiguring Storage Access Controls and Uniform Bucket-Level Access

A security auditor requires your team to standardize security controls on an active production Cloud Storage bucket currently configured with fine-grained access control. You must transition this bucket to enforce Uniform Bucket-Level Access (UBLA) without causing access disruptions for authorized applications and service accounts. Arrange the operational steps in the correct chronological sequence to safely complete this security migration.

  1. 1Audit existing object-level and bucket-level Access Control Lists (ACLs) to catalog all individual user and service account permissions.
  2. 2Grant equivalent predefined Cloud IAM storage roles (such as Storage Object Viewer or Storage Object Admin) at the bucket level to the identified principals.
  3. 3Enable Uniform Bucket-Level Access on the bucket by running `gcloud storage buckets update gs://[BUCKET_NAME] --uniform-bucket-level-access`.
  4. 4Monitor Cloud Audit Logs and application traffic during the 90-day grace period to verify that all authorization requests succeed under IAM policy evaluation.
  5. 5Lock Uniform Bucket-Level Access on the bucket to permanently prevent disabling UBLA or reapplying fine-grained ACL controls.

Answer

The correct operational order for migrating to Uniform Bucket-Level Access is: 1) Audit existing object and bucket ACLs, 2) Grant equivalent IAM roles at the bucket level, 3) Enable Uniform Bucket-Level Access using the CLI, 4) Monitor access logs during the grace period, and 5) Lock Uniform Bucket-Level Access permanently.
Safely transitioning a bucket from fine-grained ACLs to Uniform Bucket-Level Access requires a structured approach: auditing existing ACL access, mapping those permissions to appropriate Cloud IAM predefined roles at the bucket level, activating UBLA via gcloud, validating application behavior during the 90-day grace period, and finally locking the UBLA policy to enforce compliance permanently.

Step-by-Step Solution

1
Audit current ACL entries on the bucket and its objects.
Identified all users, groups, and service accounts relying on per-object fine-grained permissions.
You must understand current access permissions before replacing them with bucket-level IAM policies to avoid service disruption.
2
Assign corresponding IAM roles to principals at the bucket level.
Principals receive bucket-wide IAM permissions equivalent to their previous ACL permissions.
Enabling UBLA causes Google Cloud Storage to ignore ACLs; IAM roles must already be active before UBLA is turned on.
3
Execute `gcloud storage buckets update gs://[BUCKET_NAME] --uniform-bucket-level-access`.
Uniform Bucket-Level Access is enabled on the target bucket.
This configuration change shifts access evaluation exclusively to Cloud IAM roles.
4
Review audit logs and monitor workload access during the 90-day evaluation window.
Access validation confirms no authorized workloads are blocked.
The 90-day grace period allows administrators to revert UBLA if unmapped ACL permissions break critical workflows.
5
Lock Uniform Bucket-Level Access using `gcloud storage buckets update gs://[BUCKET_NAME] --lock-uniform-bucket-level-access`.
The bucket policy is locked and UBLA can no longer be disabled.
Locking ensures compliance with security regulations by permanently prohibiting fine-grained ACL access controls.

Key Concept

Migrating to Uniform Bucket-Level Access (UBLA)
Rate this question