---
prelude: |
    The 16.0.0 release includes many new features and bug fixes. It is
    difficult to cover all the changes that have been introduced. Please at
    least read the upgrade section which describes the required actions to
    upgrade your cloud from 15.0.0 (Ocata) to 16.0.0 (Pike).

    That said, a few major changes are worth mentioning. This is not an
    exhaustive list:

    - The latest Compute API microversion supported for Ocata is v2.53. Details
      on REST API microversions added since the 15.0.0 Ocata release can be
      found in the `REST API Version History`_ page.
    - The FilterScheduler driver now provides allocations to the Placement API,
      which helps concurrent schedulers to verify resource consumptions
      directly without waiting for compute services to ask for a reschedule in
      case of a race condition. That is an important performance improvement
      that includes allowing one to use more than one scheduler worker if
      there are capacity concerns. For more details, see the
      `Pike Upgrade Notes for Placement`_.
    - Nova now supports a Cells v2 multi-cell deployment. The default
      deployment is a single cell. There are known `limitations with
      multiple cells`_. Refer to the `Cells v2 Layout`_ page for more
      information about deploying multiple cells.
    - Cells v1 is now deprecated in favor of Cells v2.
    - The quota system has been reworked to `count resources`_ at the point of
      creation rather than using a reserve/commit/rollback approach. No
      operator impacts are expected.
    - Compute-specific documentation is being migrated from
      http://docs.openstack.org to https://docs.openstack.org/nova/ and the
      layout for the Nova developer documentation is being re-organized. If you
      think anything is missing or you now have broken bookmarks, please
      `report a bug`_.

    .. _Pike Upgrade Notes for Placement: https://docs.openstack.org/nova/latest/user/placement.html#pike-16-0-0

    .. _limitations with multiple cells: https://docs.openstack.org/nova/latest/user/cellsv2_layout.html#caveats-of-a-multi-cell-deployment

    .. _Cells v2 Layout: https://docs.openstack.org/nova/latest/user/cellsv2_layout.html

    .. _count resources: https://specs.openstack.org/openstack/nova-specs/specs/pike/approved/cells-count-resources-to-check-quota-in-api.html

    .. _report a bug: https://bugs.launchpad.net/nova/
