It is recommended to use uniform bucket-level access to unify and simplify how you grant access to your Cloud Storage resources. Cloud Storage offers two systems for granting users permission to access your buckets and objects: Cloud Identity and Access Management (Cloud IAM) and Access Control Lists (ACLs). These systems act in parallel - in order for a user to access a Cloud Storage resource, only one of the systems needs to grant the user permission. Cloud IAM is used throughout Google Cloud and allows you to grant a variety of permissions at the bucket and project levels. ACLs are used only by Cloud Storage and have limited permission options, but they allow you to grant permissions on a per-object basis.
In order to support a uniform permissioning system, Cloud Storage has uniform bucket-level access. Using this feature disables ACLs for all Cloud Storage resources: access to Cloud Storage resources then is granted exclusively through Cloud IAM. Enabling uniform bucket-level access guarantees that if a Storage bucket is not publicly accessible, no object in the bucket is publicly accessible either.
Open the Cloud Storage browser in the Google Cloud Console
In the list of buckets, click on the name of the desired bucket.
Select the Permissions tab near the top of the page.
In the text box in which it is written as Access control click Switch to Uniform
In the pop-up menu that appears, select Uniform
Select the Add project role ACLs to the bucket IAM policy checkbox
Click Save
