Add docs for compute capabilities as traits
Change I15364d37fb7426f4eec00ca4eaf99bec50e964b6 added the ability for the compute service to report a subset of driver capabilities as standard COMPUTE_* traits on the compute node resource provider. This adds administrator documentation to the scheduler docs about the feature and how it could be used with flavors. There are also some rules and semantic behavior around how these traits work so that is also documented. Note that for cases #3 and #4 in the "Rules" section the update_available_resource periodic task in the compute service may add the compute-owned traits again automatically but it depends on the [compute]/resource_provider_association_refresh configuration option, which if set to 0 will disable that auto refresh and a restart or SIGHUP is required. To avoid confusion in these docs, I have opted to omit the mention of that option and just document the action that will work regardless of configuration which is to restart or SIGHUP the compute service. Change-Id: Iaeec92e0b25956b0d95754ce85c68c2d82c4a7f1
This commit is contained in:
Matt Riedemann
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926e584136
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c16c3062e7
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@ -307,6 +307,8 @@ features in some virt drivers and querying traits is efficient. For more detail,
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:ref:`Forbidden traits <extra-specs-forbidden-traits>` and
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`Report CPU features to the Placement service <https://specs.openstack.org/openstack/nova-specs/specs/rocky/approved/report-cpu-features-as-traits.html>`_.
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Also refer to `Compute capabilities as traits`_.
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.. _ComputeFilter:
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ComputeFilter
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@ -1037,6 +1039,8 @@ nova service-disable [--reason <reason>] <id>
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ERROR: Policy doesn't allow compute_extension:hosts to be performed. (HTTP 403) (Request-ID: req-ef2400f6-6776-4ea3-b6f1-7704085c27d1)
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.. _config-sch-for-aggs:
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Configure scheduler to support host aggregates
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----------------------------------------------
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@ -1449,3 +1453,72 @@ related commands. To enable or disable a cell, use
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:command:`nova-manage cell_v2 update_cell` and to create pre-disabled cells,
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use :command:`nova-manage cell_v2 create_cell`. See the
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:ref:`man-page-cells-v2` man page for details on command usage.
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Compute capabilities as traits
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Starting with the 19.0.0 Stein release, the ``nova-compute`` service will
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report certain ``COMPUTE_*`` traits based on its compute driver capabilities
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to the placement service. The traits will be associated with the resource
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provider for that compute service. These traits can be used during scheduling
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by configuring flavors with
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:ref:`Required traits <extra-specs-required-traits>` or
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:ref:`Forbidden traits <extra-specs-forbidden-traits>`. For example, if you
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have a host aggregate with a set of compute nodes that support multi-attach
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volumes, you can restrict a flavor to that aggregate by adding the
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``trait:COMPUTE_VOLUME_MULTI_ATTACH=required`` extra spec to the flavor and
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then restrict the flavor to the aggregate
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:ref:`as normal <config-sch-for-aggs>`.
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Here is an example of a libvirt compute node resource provider that is
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exposing some CPU features as traits, driver capabilities as traits, and a
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custom trait denoted by the ``CUSTOM_`` prefix:
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.. code-block:: console
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$ openstack --os-placement-api-version 1.6 resource provider trait list \
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> d9b3dbc4-50e2-42dd-be98-522f6edaab3f --sort-column name
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+---------------------------------------+
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| name |
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+---------------------------------------+
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| COMPUTE_DEVICE_TAGGING |
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| COMPUTE_NET_ATTACH_INTERFACE |
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| COMPUTE_NET_ATTACH_INTERFACE_WITH_TAG |
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| COMPUTE_TRUSTED_CERTS |
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| COMPUTE_VOLUME_ATTACH_WITH_TAG |
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| COMPUTE_VOLUME_EXTEND |
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| COMPUTE_VOLUME_MULTI_ATTACH |
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| CUSTOM_IMAGE_TYPE_RBD |
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| HW_CPU_X86_MMX |
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| HW_CPU_X86_SSE |
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| HW_CPU_X86_SSE2 |
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| HW_CPU_X86_SVM |
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+---------------------------------------+
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**Rules**
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There are some rules associated with capability-defined traits.
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1. The compute service "owns" these traits and will add/remove them when the
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``nova-compute`` service starts and when the ``update_available_resource``
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periodic task runs, with run intervals controlled by config option
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:oslo.config:option:`update_resources_interval`.
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2. The compute service will not remove any custom traits set on the resource
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provider externally, such as the ``CUSTOM_IMAGE_TYPE_RBD`` trait in the
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example above.
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3. If compute-owned traits are removed from the resource provider externally,
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for example by running ``openstack resource provider trait delete <rp_uuid>``,
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the compute service will add its traits again on restart or SIGHUP.
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4. If a compute trait is set on the resource provider externally which is not
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supported by the driver, for example by adding the ``COMPUTE_VOLUME_EXTEND``
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trait when the driver does not support that capability, the compute service
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will automatically remove the unsupported trait on restart or SIGHUP.
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5. Compute capability traits are standard traits defined in the `os-traits`_
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library.
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.. _os-traits: http://git.openstack.org/cgit/openstack/os-traits/tree/os_traits/compute
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