ac1e0f8afe
In the top index page of the document, some sections had actual contents and some had only links to the contents. However, this makes it difficult for readers to get what is in the document and what isn't at a glance. This patch cleans it up to simplify the top index. This patch also renames some of the directories to follow the doc layout rules[1]. [1] https://specs.openstack.org/openstack/docs-specs/specs/pike/os-manuals-migration.html Note that the following ToDo is left for further cleanup: * Publish the api guide and move the microversion history to the `/api-guide` directory Change-Id: Ideb1d5e7c74d1d564d07bac1a1e7c86c55ede873
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..
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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://docs.openstack.org/api-ref/placement/
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.. _creating the resource provider: https://docs.openstack.org/api-ref/placement/?expanded=create-resource-provider-detail#create-resource-provider
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.. _setting the inventory: https://docs.openstack.org/api-ref/placement/?expanded=update-resource-provider-inventories-detail#update-resource-provider-inventories
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.. _setting the traits: https://docs.openstack.org/api-ref/placement/?expanded=update-resource-provider-traits-detail#update-resource-provider-traits
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.. _allocation candidates: https://docs.openstack.org/api-ref/placement/?expanded=list-allocation-candidates-detail#list-allocation-candidates
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.. _allocation: https://docs.openstack.org/api-ref/placement/?expanded=update-allocations-detail#update-allocations
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REST API
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========
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The placement API service provides a well-documented, JSON-based `HTTP API`_
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and data model. It is designed to be easy to use from whatever HTTP client is
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suitable. There is a plugin to the openstackclient_ command line tool called
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osc-placement_ which is useful for occasional inspection and manipulation of
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the resources in the placement service.
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.. _HTTP API: https://docs.openstack.org/api-ref/placement/
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.. _openstackclient: https://pypi.org/project/openstackclient/
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.. _osc-placement: https://pypi.org/project/osc-placement/
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Microversions
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-------------
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The placement API uses microversions for making incremental changes to the
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API which client requests must opt into.
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It is especially important to keep in mind that nova-compute is a client of
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the placement REST API and based on how Nova supports rolling upgrades the
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nova-compute service could be Newton level code making requests to an Ocata
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placement API, and vice-versa, an Ocata compute service in a cells v2 cell
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could be making requests to a Newton placement API.
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This history of placement microversions may be found in the following
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subsection.
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.. toctree::
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:maxdepth: 2
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../placement-api-microversion-history
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