# Understanding Nova Policies

Warning

JSON formatted policy file is deprecated since Nova 22.0.0(Victoria). Use YAML formatted file. Use oslopolicy-convert-json-to-yaml tool to convert the existing JSON to YAML formatted policy file in backward compatible way.

Nova supports a rich policy system that has evolved significantly over its lifetime. Initially, this took the form of a large, mostly hand-written `policy.yaml` file but, starting in the Newton (14.0.0) release, policy defaults have been defined in the codebase, requiring the `policy.yaml` file only to override these defaults.

In the Ussuri (21.0.0) release, further work was undertaken to address some issues that had been identified:

1. No global vs project admin. The `admin_only` role is used for the global admin that is able to make almost any change to Nova, and see all details of the Nova system. The rule passes for any user with an admin role, it doesn’t matter which project is used.

2. No read-only roles. Since several APIs tend to share a single policy rule for read and write actions, they did not provide the granularity necessary for read-only access roles.

3. The `admin_or_owner` role did not work as expected. For most APIs with `admin_or_owner`, the project authentication happened in a separate component than API in Nova that did not honor changes to policy. As a result, policy could not override hard-coded in-project checks.

Keystone comes with `admin`, `member` and `reader` roles by default. Please refer to this document for more information about these new defaults. In addition, keystone supports a new “system scope” concept that makes it easier to protect deployment level resources from project or system level resources. Please refer to this document and system scope specification to understand the scope concept.

In the Nova 25.0.0 (Yoga) release, Nova policies implemented the scope concept and default roles provided by keystone (admin, member, and reader). Using common roles from keystone reduces the likelihood of similar, but different, roles implemented across projects or deployments (e.g., a role called `observer` versus `reader` versus `auditor`). With the help of the new defaults it is easier to understand who can do what across projects, reduces divergence, and increases interoperability.

The below sections explain how these new defaults in the Nova can solve the first two issues mentioned above and extend more functionality to end users in a safe and secure way.

More information is provided in the nova specification.

## Scope

OpenStack Keystone supports different scopes in tokens. These are described here. Token scopes represent the layer of authorization. Policy `scope_types` represent the layer of authorization required to access an API.

Note

The `scope_type` of each policy is hardcoded and is not overridable via the policy file.

Nova policies have implemented the scope concept by defining the `scope_type` in policies. To know each policy’s `scope_type`, please refer to the Policy Reference and look for `Scope Types` or `Intended scope(s)` in Policy Sample File as shown in below examples.

`system` scope

Policies with a `scope_type` of `system` means a user with a `system-scoped` token has permission to access the resource. This can be seen as a global role. All the system-level operation’s policies have defaulted to `scope_type` of `['system']`.

For example, consider the `GET /os-hypervisors` API.

    # List all hypervisors.
    # GET  /os-hypervisors
    # Intended scope(s): system
    #"os_compute_api:os-hypervisors:list": "rule:system_reader_api"

`project` scope

Policies with a `scope_type` of `project` means a user with a `project-scoped` token has permission to access the resource. Project-level only operation’s policies are defaulted to `scope_type` of `['project']`.

For example, consider the `POST /os-server-groups` API.

    # Create a new server group
    # POST  /os-server-groups
    # Intended scope(s): project
    #"os_compute_api:os-server-groups:create": "rule:project_member_api"

`system and project` scope

Policies with a `scope_type` of `system and project` means a user with a `system-scoped` or `project-scoped` token has permission to access the resource. All the system and project level operation’s policies have defaulted to `scope_type` of `['system', 'project']`.

For example, consider the `GET /flavors/{flavor_id}/os-extra_specs/{flavor_extra_spec_key}` API.

    # Show an extra spec for a flavor
    # GET /flavors/{flavor_id}/os-extra_specs/{flavor_extra_spec_key}
    # Intended scope(s): system, project
    #"os_compute_api:os-flavor-extra-specs:show": "rule:project_reader_or_admin"

These scope types provide a way to differentiate between system-level and project-level access roles. You can control the information with scope of the users. This means you can control that none of the project level role can get the hypervisor information.

Policy scope is disabled by default to allow operators to migrate from the old policy enforcement system in a graceful way. This can be enabled by configuring the `oslo_policy.enforce_scope` option to `True`.

Note

[oslo_policy] enforce_scope=True

## Roles

You can refer to this document to know about all available defaults from Keystone.

Along with the `scope_type` feature, Nova policy defines new defaults for each policy.

`reader`

This provides read-only access to the resources within the `system` or `project`. Nova policies are defaulted to below rules:

    system_reader_api
       Default
          role:reader and system_scope:all

    system_or_project_reader
       Default
          (rule:system_reader_api) or (role:reader and project_id:%(project_id)s)

`member`

This role is to perform the project level write operation with combination to the system admin. Nova policies are defaulted to below rules:

    project_member_api
       Default
          role:member and project_id:%(project_id)s

    system_admin_or_owner
       Default
          (role:admin and system_scope:all) or (role:member and project_id:%(project_id)s)

`admin`

This role is to perform the admin level write operation at system as well as at project-level operations. Nova policies are defaulted to below rules:

    system_admin_api
       Default
          role:admin and system_scope:all

    project_admin_api
       Default
          role:admin and project_id:%(project_id)s

    system_admin_or_owner
       Default
          (role:admin and system_scope:all) or (role:member and project_id:%(project_id)s)

With these new defaults, you can solve the problem of:

1. Providing the read-only access to the user. Polices are made more granular and defaulted to reader rules. For exmaple: If you need to let someone audit your deployment for security purposes.

2. Customize the policy in better way. For example, you will be able to provide access to project level user to perform live migration for their server or any other project with their token.

## Nova supported scope & Roles

Nova supports the below combination of scopes and roles where roles can be overridden in the policy.yaml file but scope is not override-able.

1. ADMIN: `admin` role on `system` scope. This is System Administrator to perform the system level resource operations. Example: enable/disable compute services.

2. PROJECT_ADMIN: `admin` role on `project` scope. This is used to perform admin level operation within project. For example: Live migrate server.

   Note

   PROJECT_ADMIN has the limitation for the below policies

   - `os_compute_api:servers:create:forced_host`

   - `os_compute_api:servers:compute:servers:create:requested_destination`

   To create a server on specific host via force host or requested destination, you need to pass the hostname in `POST /servers` API request but there is no way for PROJECT_ADMIN to get the hostname via API. This limitation will be addressed in a future release.

3. PROJECT_MEMBER: `member` role on `project` scope. This is used to perform resource owner level operation within project. For example: Pause a server.

4. PROJECT_READER: `reader` role on `project` scope. This is used to perform read-only operation within project. For example: Get server.

5. PROJECT_READER_OR_ADMIN: `admin` role on `system` scope or `reader` role on `project` scope. Such policy rules are scoped as both `system` as well as `project`. Example: to allow system admin and project reader to list flavor extra specs.

   Note

   As of now, only `system` and `project` scopes are supported in Nova.

## Backward Compatibility

Backward compatibility with versions prior to 21.0.0 (Ussuri) is maintained by supporting the old defaults and disabling the `scope_type` feature by default. This means the old defaults and deployments that use them will keep working as-is. However, we encourage every deployment to switch to new policy. Scope checks are disabled by default and will be enabled by default starting Nova 26.0.0 (OpenStack Zed release) and the old defaults will be removed starting in the Nova 27.0.0 release.

To implement the new default reader roles, some policies needed to become granular. They have been renamed, with the old names still supported for backwards compatibility.

## Migration Plan

To have a graceful migration, Nova provides two flags to switch to the new policy completely. You do not need to overwrite the policy file to adopt the new policy defaults.

Here is step wise guide for migration:

1. Create scoped token:

   You need to create the new token with scope knowledge via below CLI:

   - Create System Scoped Token.

   - Create Project Scoped Token.

2. Create new default roles in keystone if not done:

   If you do not have new defaults in Keystone then you can create and re-run the Keystone Bootstrap. Keystone added this support in 14.0.0 (Rocky) release.

3. Enable Scope Checks

   The `oslo_policy.enforce_scope` flag is to enable the `scope_type` features. The scope of the token used in the request is always compared to the `scope_type` of the policy. If the scopes do not match, one of two things can happen. If `oslo_policy.enforce_scope` is True, the request will be rejected. If `oslo_policy.enforce_scope` is False, an warning will be logged, but the request will be accepted (assuming the rest of the policy passes). The default value of this flag is False.

   Note

   Before you enable this flag, you need to audit your users and make sure everyone who needs system-level access has a system role assignment in keystone.

4. Enable new defaults

   The `oslo_policy.enforce_new_defaults` flag switches the policy to new defaults-only. This flag controls whether or not to use old deprecated defaults when evaluating policies. If True, the old deprecated defaults are not evaluated. This means if any existing token is allowed for old defaults but is disallowed for new defaults, it will be rejected. The default value of this flag is False.

   Note

   Before you enable this flag, you need to educate users about the different roles they need to use to continue using Nova APIs.

5. Check for deprecated policies

   A few policies were made more granular to implement the reader roles. New policy names are available to use. If old policy names which are renamed are overwritten in policy file, then warning will be logged. Please migrate those policies to new policy names.

Below table show how legacy rules are mapped to new rules:

Legacy Rules | New Rules |  |
--- | --- | --- | ---
Project Admin Role |  | Roles | Scope
ADMIN | admin | system project
PROJECT_ADMIN | admin
Project admin or owner role | PROJECT_ADMIN | admin | project
PROJECT_MEMBER | member
PROJECT_READER | reader
PROJECT_READER_OR_ADMIN | admin on system or reader on project | system OR project

We expect all deployments to migrate to new policy by 27.0.0 release so that we can remove the support of old policies.

this page last updated: 2026-06-10 20:07:09

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