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