Access Control Lists (ACL) are a means to grant and deny access to buckets and objects. Each bucket and object will have an ACL associated with it. A default ACL is created when a bucket or object is created that grants full control to the creating party and denies access to all other parties. The Riak CS ACLs are modeled after S3 ACLs. For more information, see the Amazon Access Control List Overview documentation.

Representations

XML is the only supported external format for ACLs. In the future other formats such as JSON may be supported.

Example XML representation of an ACL:

<xml version="1.0" encoding="UTF-8">
<AccessControlPolicy xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
  <Owner>
    <ID>abcd123</ID>
    <DisplayName>joebob</DisplayName>
  </Owner>
  <AccessControlList>
    <Grant>
      <Grantee xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="Canonical User">
        <ID>abcd123</ID>
        <DisplayName>joebob</DisplayName>
      </Grantee>
      <Permission>FULL_CONTROL</Permission>
    </Grant>
  </AccessControlList>
</AccessControlPolicy>

Permissions

Bucket Permissions

• READ - Grantee may list the objects in the bucket
• READ_ACP - Grantee may read the bucket ACL
• WRITE - Grantee may create, overwrite, and delete any object in the bucket
• WRITE_ACP - Grantee may write the ACL for the applicable bucket
• FULL_CONTROL - Grantee has READ, WRITE, READ_ACP, and WRITE_ACP permissions on the bucket

Object Permissions

• READ - Grantee may read the object data and its metadata
• READ_ACP - Grantee may read the object ACL. Note: The object owner may read the object ACL even if not explicitly granted READ_ACP permission.
• WRITE_ACP - Grantee may write the ACL for the applicable object. Note: The object owner may write the object ACL even if not explicitly granted WRITE_ACP permission.
• FULL_CONTROL - Grantee has READ, READ_ACP, and WRITE_ACP permissions on the object

Buckets

Bucket names must be globally unique. To avoid conflicts all bucket creation requests are made to an application called stanchion; therefore, all requests for modification of a bucket ACL should be serialized through stanchion. While this will cause undesirable serialization of these requests, we believe it is appropriate based on the following statement from this documentation on bucket restrictions from Amazon regarding restrictions on bucket operations:

Because bucket operations work against a centralized, global resource space, it is not appropriate to make bucket create or delete calls on the high availability code path of your application.

This statement only directly references create or delete calls, but we have taken a more broad interpretation to include requests that modify the ACL.

Objects

The object ACL is stored with each object as a metadata field. If no ACL information is present in the object creation request a default ACL is created granting the creator both ownership and full access control and denying access to all other parties.