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Access Control Lists

Access Control Lists (ACLs) are a means of granting and denying access to buckets and objects. Each bucket and object in a Riak CS cluster will have an ACL associated with it. When a bucket or object is created, a default ACL will be created alongside it that grants full control to the creating party and denies access to all other parties.

Riak CS ACLs are modeled after S3 ACLs. For more information, see the Amazon Access Control List Overview documentation.

ACL Limit

An ACL can have up to 100 grants.


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="">
      <Grantee xmlns:xsi="" xsi:type="Canonical User">


Riak CS permissions are split into two types: bucket permissions and object permissions.

Bucket Permissions

Object Permissions


Bucket names must be globally unique. To avoid conflicts, all bucket creation requests are made to an application called Stanchion. This means that all requests for modification of a bucket ACL should be serialized through Stanchion. While this may 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.


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.

For information on specifying an ACL when making a PUT request, see RiakCS PUT Object ACL.