openstack/nova
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Add docs for image type support request filter

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This adds the missing "prefilter" stage to the description of the
scheduling process, and adds information about the image type
filter.

Related to blueprint request-filter-image-types

Change-Id: I07eef048cf2c85a3fdb8adbe38e362878e4e177e
This commit is contained in:
Dan Smith 2019-05-03 13:03:04 -07:00
parent 1ee0e58446
commit d4c8725940
1 changed files with 26 additions and 0 deletions
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26
doc/source/admin/configuration/schedulers.rst
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@ -51,6 +51,32 @@ target host. For information about instance evacuation, see
.. _compute-scheduler-filters:
Prefiltering
~~~~~~~~~~~~
As of the Rocky release, the scheduling process includes a prefilter
step to increase the efficiency of subsequent stages. These prefilters
are largely optional, and serve to augment the request that is sent to
placement to reduce the set of candidate compute hosts based on
attributes that placement is able to answer for us ahead of time. In
addition to the prefilters listed here, also see `Tenant Isolation
with Placement`_ and `Availability Zones with Placement`_.
Compute Image Type Support
--------------------------
Starting in the Train release, there is a prefilter available for
excluding compute nodes that do not support the ``disk_format`` of the
image used in a boot request. This behavior is enabled by setting
:oslo.config:option:`[scheduler]/query_placement_for_image_type_support=True
<scheduler.query_placement_for_image_type_support>`. For
example, the libvirt driver, when using ceph as an ephemeral backend,
does not support ``qcow2`` images (without an expensive conversion
step). In this case (and especially if you have a mix of ceph and
non-ceph backed computes), enabling this feature will ensure that the
scheduler does not send requests to boot a ``qcow2`` image to computes
backed by ceph.
Filter scheduler
~~~~~~~~~~~~~~~~