---
deprecations:
  - |
    The ``[scheduler] driver`` config option has been deprecated. This was
    previously used to switch between different scheduler drivers including
    custom, out-of-tree ones. However, only the ``FilterScheduler`` has been
    supported in-tree since 19.0.0 (Stein) and nova increasingly relies on
    placement for basic functionality, meaning developing and maintaining
    out-of-tree drivers is increasingly difficult. Users who still rely on a
    custom scheduler driver should migrate to the filter scheduler, using
    custom filters and weighters where necessary.