---
prelude: |
    The 21.0.0 release includes many new features and bug fixes. Please be
    sure to read the upgrade section which describes the required actions to
    upgrade your cloud from 20.0.0 (Train) to 21.0.0 (Ussuri).

    There are a few major changes worth mentioning. This is not an exhaustive
    list:

    - The latest Compute API microversion supported for Ussuri is v2.87.
      Details on REST API microversions added since the 20.0.0 Train release
      can be found in the `REST API Version History`__ page.

      .. __: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html

    - `Image pre-caching support to compute hosts`__ using ``os-aggregates``
      API information, allowing some distributed edge cases and preemptive
      image caching for instance creation.

      .. __: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#id74

    - Support for `cold migrating and resizing servers between Nova cells`__.

      .. __: https://docs.openstack.org/nova/latest/admin/configuration/cross-cell-resize.html

    - Added support for `evacuate, live migrate and unshelve servers with
      minimum bandwidth guarantees`__.

      .. __: https://docs.openstack.org/api-guide/compute/port_with_resource_request.html

    - New ``nova-manage placement audit`` CLI command to `find and clean up
      orphaned resource allocations`__.

      .. __: https://docs.openstack.org/nova/latest/cli/nova-manage.html

    - Support for scope types and additional roles in the default nova
      policies, allowing for richer access management including the ability to
      configure *read-only* access to resources. This feature is disabled by
      default. See the `Policy Concepts`__ documentation for more details.

      .. __: https://docs.openstack.org/nova/latest/configuration/policy-concepts.html

    - Support for `creating servers with accelerator devices via Cyborg`__.

      .. __: https://docs.openstack.org/api-guide/compute/accelerator-support.html

    - Enabled `rescue for boot-from-volume instances`__. Rescue now also allows
      to attach stable disk devices to the rescued instance.

      .. __: https://docs.openstack.org/nova/latest/user/rescue.html

    - Validation for `known flavor extra specs with recognized namespaces`__.

      .. __: https://docs.openstack.org/nova/latest/reference/api-microversion-history.html#id79

    - Support for `heterogenous virtual GPU types per compute node`__.

      .. __: https://docs.openstack.org/nova/latest/admin/virtual-gpu.html#enable-gpu-types-compute

    - Python 2 is no longer supported by Nova, Python 3.6 and 3.7 are.

    - Removal of the ``os-consoles`` and ``os-networks`` REST APIs. See the
      `Upgrade Notes`_ section for more details.

    - Removal of the ``nova-dhcpbridge``, ``nova-console`` and
      ``nova-xvpvncproxy`` services. See the `Upgrade Notes`_ section for more
      details.