af99d9e4e1
There wasn't really a good overview on how to use placement, so I've tried to start something by expanding on how nova uses placement in very broad strokes. The intent here is not to instruct people on the details of how to manage resources with placement, rather that they _can_ manage resources with placement and here's the major steps involved. Change-Id: I11cd622162efce2e87a21fa5ae5d297f4b248541
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Licensed under the Apache License, Version 2.0 (the "License"); you may
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not use this file except in compliance with the License. You may obtain
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a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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License for the specific language governing permissions and limitations
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under the License.
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=================
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Placement Usage
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=================
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Tracking Resources
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==================
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The placement service enables other projects to track their own resources.
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Those projects can register/delete their own resources to/from placement
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via the placement `HTTP API`_.
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The placement service originated in the :nova-doc:`Nova project </>`. As a
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result much of the functionality in placement was driven by nova's
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requirements. However, that functionality was designed to be sufficiently
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generic to be used by any service that needs to manage the selection and
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consumption of resources.
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How Nova Uses Placement
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-----------------------
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Two processes, ``nova-compute`` and ``nova-scheduler``, host most of nova's
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interaction with placement.
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The nova resource tracker in ``nova-compute`` is responsible for `creating the
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resource provider`_ record corresponding to the compute host on which the
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resource tracker runs, `setting the inventory`_ that describes the quantitative
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resources that are available for workloads to consume (e.g., ``VCPU``), and
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`setting the traits`_ that describe qualitative aspects of the resources (e.g.,
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``STORAGE_DISK_SSD``).
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If other projects -- for example, Neutron or Cyborg -- wish to manage resources
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on a compute host, they should create resource providers as children of the
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compute host provider and register their own managed resources as inventory on
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those child providers. For more information, see the
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:doc:`Modeling with Provider Trees <provider-tree>`.
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The ``nova-scheduler`` is responsible for selecting a set of suitable
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destination hosts for a workload. It begins by formulating a request to
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placement for a list of `allocation candidates`_. That request expresses
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quantitative and qualitative requirements, membership in aggregates, and in
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more complex cases, the topology of related resources. That list is reduced and
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ordered by filters and weighers within the scheduler process. An `allocation`_
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is made against a resource provider representing a destination, consuming a
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portion of the inventory set by the resource tracker.
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.. toctree::
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:hidden:
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provider-tree
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.. _HTTP API: https://developer.openstack.org/api-ref/placement/
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.. _creating the resource provider: https://developer.openstack.org/api-ref/placement/?expanded=create-resource-provider-detail#create-resource-provider
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.. _setting the inventory: https://developer.openstack.org/api-ref/placement/?expanded=update-resource-provider-inventories-detail#update-resource-provider-inventories
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.. _setting the traits: https://developer.openstack.org/api-ref/placement/?expanded=update-resource-provider-traits-detail#update-resource-provider-traits
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.. _allocation candidates: https://developer.openstack.org/api-ref/placement/?expanded=list-allocation-candidates-detail#list-allocation-candidates
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.. _allocation: https://developer.openstack.org/api-ref/placement/?expanded=update-allocations-detail#update-allocations
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