46 lines
2.5 KiB
YAML
46 lines
2.5 KiB
YAML
---
|
|
upgrade:
|
|
- |
|
|
The ``caching_scheduler`` scheduler driver, which was deprecated in the
|
|
16.0.0 Pike release, has now been removed. Unlike the default
|
|
``filter_scheduler`` scheduler driver which creates resource allocations
|
|
in the placement service during scheduling, the ``caching_scheduler``
|
|
driver did not interface with the placement service. As more and more
|
|
functionality within nova relies on managing (sometimes complex) resource
|
|
allocations in the placement service, compatibility with the
|
|
``caching_scheduler`` driver is difficult to maintain, and seldom tested.
|
|
The original reasons behind the need for the CachingScheduler should now
|
|
be resolved with the FilterScheduler and the placement service, notably:
|
|
|
|
* resource claims (allocations) are made atomically during scheduling to
|
|
alleviate the potential for racing to concurrently build servers on the
|
|
same compute host which could lead to failures
|
|
* because of the atomic allocation claims made during scheduling by the
|
|
``filter_scheduler`` driver, it is safe [1]_ to run multiple scheduler
|
|
workers and scale horizontally
|
|
|
|
.. [1] There are still known race issues with concurrently building some
|
|
types of resources and workloads, such as anything that requires
|
|
PCI/NUMA or (anti-)affinity groups. However, those races also existed
|
|
with the ``caching_scheduler`` driver.
|
|
|
|
To migrate from the CachingScheduler to the FilterScheduler, operators can
|
|
leverage the ``nova-manage placement heal_allocations`` command:
|
|
|
|
https://docs.openstack.org/nova/latest/cli/nova-manage.html#placement
|
|
|
|
Finally, it is still technically possible to load an out-of-tree scheduler
|
|
driver using the ``nova.scheduler.driver`` entry-point. However,
|
|
out-of-tree driver interfaces are not guaranteed to be stable:
|
|
|
|
https://docs.openstack.org/nova/latest/contributor/policies.html#out-of-tree-support
|
|
|
|
And as noted above, as more of the code base evolves to rely on resource
|
|
allocations being tracked in the placement service (created during
|
|
scheduling), out-of-tree scheduler driver support may be severely impacted.
|
|
|
|
If you rely on the ``caching_scheduler`` driver or your own out-of-tree
|
|
driver which sets ``USES_ALLOCATION_CANDIDATES = False`` to bypass the
|
|
placement service, please communicate with the nova development team in
|
|
the openstack-dev mailing list and/or #openstack-nova freenode IRC channel
|
|
to determine what prevents you from using the ``filter_scheduler`` driver. |