Policy Merge in Keystone

Policy Merge in Keystone

bp example

Managing Policy By composing Fragments in the Keystone server.

Problem Description

Policy in OpenStack is incredibly Static. Coupled with that, the defaults are not set up to scale. However, changing policy cluster wide is a difficult task.

Many of the policy files have common sections, or section that vary slightly, but use the same rule names. This has the potential to confuse deployers, as well as contribute to security holes.

While each of the project teams needs to be able maintain their own inventory of policy targets, they should be able to consume a common section from Keystone. Composing that common section is going to be a work in progress, and needs support from the Keystone server.

With the various APIs for associating policy files with endpoints and services, Keystone now has a way to act as a system of record for policy. However, the policy files themselves are still opaque blobs, disjoint between services.

Proposed Change

Add a CLI for creating a new policy file by merging a set of existing policy files.

For an initial implementation, Keystone will assume all of the policy files are JSON files. They will be parsed, and the set of rules merged into a single JSON file, which will be deserialized.

Once YAML is supported by oslo.policy, it will be handled the same way.

A parameter will indicate how to treat conflicts between existing rules. This paramter can be specificied once globally, and also per file:

The strategies are:
  • FAIL: If two rules have the same key, the API will return an error code.
  • OVERRIDE: If two rules have the same key, the rule from the later file in the list will over-write the rule specified by the earlier file.
  • MAINTAIN: The first specification of a rule will be maintained, and conflicting definitions will be discarded.
Once the merger is complete, a new policy file will be produced in JSON format.


Merging and composing of the JSON blobs could be done off line. However, this is merely another way of implementing the same function, but without integrating it in with OpenStack.

Security Impact

As with most policy changes, this is designed to improve the security story of OpenStack deployments. By itself, this change will have no impact. However, when coupled with the ability to distribute policy files based on the associations, the policy will be more dynamic, and can lead to an improvement or degradation based on the quality of the review and distribution process.

Notifications Impact

There is no notification impact.

Other End User Impact

Deployers can make use of this call to create more specific policies.

One expected use case is to allow a user to override a small set of APIs from the basic policy for a service.

OpenStack Client will also need an option to trigger the call.

Performance Impact

None, calls to this CLI should be done at deployment time or earlier.

Other Deployer Impact

This is a work flow change, but will not materially impact the general deployment of OpenStack until tooling takes advantage of the Associations. Once that happens, the overall work flow will look like this:

  • Create a common policy fragment.
  • Create the new policy fragment.
  • Merge the Common fragment with the new
  • Distribute the associated policy file to the new endpoint.

Developer Impact

API Developers working on policy will be able to think in terms of common policy fragments.



Primary assignee: ayoung Adam Young ayoung@redhat.com

Work Items

  • Server Should be done in a single commit.
  • Client Code
  • Deployment tooling.


No external dependencies. However, the coming change to let Oslo policy render to YAML or other formats might complicate the merge process.

Documentation Impact

This should have little impact to start. Once the whole work flow is in place, it should be documented in a “How to manage policy” guide.


None Yet.

Creative Commons Attribution 3.0 License

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