Learn how to fix the “Cannot insert legacy ACL for an object when uniform bucket-level access is enabled” error. Our Google Cloud Support team is here to help you with your questions and concerns.

”Cannot insert legacy ACL for an object when uniform bucket-level access is enabled.”

UBLA, short for Uniform Bucket-Level Access, is a powerful feature in cloud storage services like Google Cloud Storage and Amazon S3. It simplifies and strengthens access control. By applying a consistent permission model across all objects in a bucket, UBLA eliminates the need for individual Access Control Lists (ACLs) on objects.

Today, we will explore UBLA and how to solve the “Cannot Get Legacy ACL for an Object” error.

An Overview:

• What is Uniform Bucket-Level Access (UBLA)?
• Impact on Legacy ACLs
• Common Error: “Cannot Get Legacy ACL for an Object”
• How to Resolve the Error
• Step 1: Stop Using ACLs
• Step 2: Check if UBLA is Enabled
• Step 3: Disable UBLA (Not Recommended)
• Recommended Approach: Adopt IAM Permissions
• Why is UBLA Beneficial?

What is Uniform Bucket-Level Access (UBLA)?

UBLA enforces a uniform access control mechanism for all objects within a storage bucket. Rather than setting permissions individually for each object, permissions are managed at the bucket level using IAM policies. Here are some of the key benefits:

• All objects inherit permissions from the bucket’s IAM policy.
• Reduces the risk of inconsistent or misconfigured object-level permissions.
• Ensures access control is standardized across the bucket, aiding in auditing and compliance.

Impact on Legacy ACLs

When UBLA is enabled, legacy object-level ACLs become obsolete. Instead:

• The bucket’s IAM policy dictates access permissions for all objects.
• Attempts to manage or retrieve individual ACLs for objects result in errors.

Common Error: “Cannot Get Legacy ACL for an Object”

This error occurs when we try to retrieve or modify an object’s ACL in a bucket where UBLA is enabled. For example:

Suppose UBLA is active for a bucket in Google Cloud Storage. Then, we try to run the following command:

gsutil acl get gs://your-bucket/your-object

Now, the system responds with this error message:

CommandException: Cannot get legacy ACL for an object when uniform bucket level access is enabled

According to our Experts, as UBLA overrides individual object ACLs, any commands or APIs attempting to manage legacy ACLs are incompatible with UBLA.

How to Resolve the Error

Step 1: Stop Using ACLs

Manage permissions through bucket-level IAM policies instead of object-level ACLs:

• Assign roles such as roles/storage.objectViewer or roles/storage.objectAdmin at the bucket level to users or service accounts.
• Use the Google Cloud Console, gsutil iam commands, or APIs to manage IAM policies.

Step 2: Check if UBLA is Enabled

To verify if UBLA is active for a bucket:

gsutil uniformbucketlevelaccess get gs://your-bucket

If it returns True, UBLA is enabled.

Step 3: Disable UBLA (Not Recommended)

If object-level ACLs are essential, we can disable UBLA:

gsutil uniformbucketlevelaccess set off gs://your-bucket

However, disabling UBLA may compromise security and consistency. Consider this option only when absolutely necessary.

Recommended Approach: Adopt IAM Permissions

Transitioning from ACLs to IAM permissions is the best practice for managing access under UBLA:

• Assign IAM roles at the bucket level for consistent access control. Here are some examples of roles:
  • roles/storage.objectViewer: Grants read access to objects.
  • roles/storage.objectAdmin: Grants full access to objects.
  • roles/storage.admin: Grants full access to the bucket and its contents.
• Manage IAM permissions via:
  • Head to the bucket via Google Cloud Console and update permissions in the Permissions tab.
  • Use gsutil iam to modify IAM policies programmatically.
  • Also, REST APIs or SDKs can be used for automated permission management.

Why is UBLA Beneficial?

• UBLA removes the complexity of managing permissions individually for thousands or millions of objects.
• Also, it reduces the risk of inconsistent or accidental permissions, ensuring robust access control.
• All objects follow a single permission model, making auditing, monitoring, and maintaining compliance easier.

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Conclusion

Uniform Bucket-Level Access (UBLA) is an effective way to manage access control in cloud storage. UBLA simplifies operations, enhances security, and ensures consistency across all objects in a bucket by enforcing bucket-level permissions and deprecating legacy ACLs. Transitioning to IAM-based permission management is key to using UBLA effectively while avoiding errors like “Cannot get legacy ACL for an object.”

In brief, our Support Experts demonstrated how to fix the “Cannot insert legacy ACL for an object when uniform bucket-level access is enabled” error.