placement/doc/source/index.rst

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===============
 Placement API
===============

Overview
========

The placement API service was introduced in the 14.0.0 Newton release within
the nova repository and extracted to the `placement repository`_ in the 19.0.0
Stein release. This is a REST API stack and data model used to track resource
provider inventories and usages, along with different classes of resources.
For example, a resource provider can be a compute node, a shared storage pool,
or an IP allocation pool. The placement service tracks the inventory and usage
of each provider. For example, an instance created on a compute node may be a
consumer of resources such as RAM and CPU from a compute node resource
provider, disk from an external shared storage pool resource provider and IP
addresses from an external IP pool resource provider.

The types of resources consumed are tracked as **classes**. The service
provides a set of standard resource classes (for example ``DISK_GB``,
``MEMORY_MB``, and ``VCPU``) and provides the ability to define custom
resource classes as needed.

Each resource provider may also have a set of traits which describe qualitative
aspects of the resource provider. Traits describe an aspect of a resource
provider that cannot itself be consumed but a workload may wish to specify. For
example, available disk may be solid state drives (SSD).

References
~~~~~~~~~~

For an overview of some of the features provided by placement, see
:doc:`Placement Usage <usage/index>`.

For a command line reference, see :doc:`cli/index`.

For installation, see the :doc:`installation reference <install/index>`.

See the :doc:`Configuration Guide <configuration/index>` for information on
configuring the system, including role-based access control policy rules.

See the :doc:`Contributor Guide <contributor/index>` for information on how to
contribute to the placement project and development processes and guidelines.

Significant feature developments are tracked in documents called specifications.
From the Train cycle onward, those documents are kept at :doc:`specs/index`.
Prior to that, Placement specifications were a part of the `Nova Specs`_.

The following specifications represent the stages of design and development of
resource providers and the Placement service. Implementation details may have
changed or be partially complete at this time.


* `Generic Resource Pools <https://specs.openstack.org/openstack/nova-specs/specs/newton/implemented/generic-resource-pools.html>`_
* `Compute Node Inventory <https://specs.openstack.org/openstack/nova-specs/specs/newton/implemented/compute-node-inventory-newton.html>`_
* `Resource Provider Allocations <https://specs.openstack.org/openstack/nova-specs/specs/newton/implemented/resource-providers-allocations.html>`_
* `Resource Provider Base Models <https://specs.openstack.org/openstack/nova-specs/specs/newton/implemented/resource-providers.html>`_
* `Nested Resource Providers`_
* `Custom Resource Classes <http://specs.openstack.org/openstack/nova-specs/specs/ocata/implemented/custom-resource-classes.html>`_
* `Scheduler Filters in DB <http://specs.openstack.org/openstack/nova-specs/specs/ocata/implemented/resource-providers-scheduler-db-filters.html>`_
* `Scheduler claiming resources to the Placement API <http://specs.openstack.org/openstack/nova-specs/specs/pike/approved/placement-claims.html>`_
* `The Traits API - Manage Traits with ResourceProvider <http://specs.openstack.org/openstack/nova-specs/specs/pike/approved/resource-provider-traits.html>`_
* `Request Traits During Scheduling`_
* `filter allocation candidates by aggregate membership`_
* `perform granular allocation candidate requests`_
* `inventory and allocation data migration`_ (reshaping provider trees)
* `handle allocation updates in a safe way`_

.. _Nested Resource Providers: http://specs.openstack.org/openstack/nova-specs/specs/queens/approved/nested-resource-providers.html
.. _Request Traits During Scheduling: https://specs.openstack.org/openstack/nova-specs/specs/queens/approved/request-traits-in-nova.html
.. _filter allocation candidates by aggregate membership: https://specs.openstack.org/openstack/nova-specs/specs/rocky/approved/alloc-candidates-member-of.html
.. _perform granular allocation candidate requests: http://specs.openstack.org/openstack/nova-specs/specs/rocky/approved/granular-resource-requests.html
.. _inventory and allocation data migration: http://specs.openstack.org/openstack/nova-specs/specs/rocky/approved/reshape-provider-tree.html
.. _handle allocation updates in a safe way: https://specs.openstack.org/openstack/nova-specs/specs/rocky/approved/add-consumer-generation.html
.. _Nova Specs: http://specs.openstack.org/openstack/nova-specs

Deployment
==========

.. note:: Before the Stein release the placement code was in Nova alongside
          the compute REST API code (nova-api). Make sure that the release
          version of this document matches the release version you want to
          deploy.

.. note:: For instructions on installing placement from Linux distribution
          packages see the :doc:`installation reference <install/index>`.
          What follows gives an overview of the process without going into
          detail on the methods used.

Steps
~~~~~

**1. Deploy the API service**

Placement provides a ``placement-api`` WSGI script for running the service with
Apache, nginx or other WSGI-capable web servers. Depending on what packaging
solution is used to deploy OpenStack, the WSGI script may be in ``/usr/bin``
or ``/usr/local/bin``.

``placement-api``, as a standard WSGI script, provides a module level
``application`` attribute that most WSGI servers expect to find. This means it
is possible to run it with lots of different servers, providing flexibility in
the face of different deployment scenarios. Common scenarios include:

* apache2_ with mod_wsgi_
* apache2 with mod_proxy_uwsgi_
* nginx_ with uwsgi_
* nginx with gunicorn_

In all of these scenarios the host, port and mounting path (or prefix) of the
application is controlled in the web server's configuration, not in the
configuration (``placement.conf``) of the placement application.

When placement was `first added to DevStack`_ it used the ``mod_wsgi`` style.
Later it `was updated`_ to use mod_proxy_uwsgi_. Looking at those changes can
be useful for understanding the relevant options.

DevStack is configured to host placement at ``/placement`` on either the
default port for http or for https (``80`` or ``443``) depending on whether TLS
is being used. Using a default port is desirable.

By default, the placement application will get its configuration for settings
such as the database connection URL from ``/etc/placement/placement.conf``.
The directory the configuration file will be found in can be changed by setting
``OS_PLACEMENT_CONFIG_DIR`` in the environment of the process that starts the
application. With recent releases of ``oslo.config``, configuration options may
also be set in the environment_.

.. note:: When using uwsgi with a front end (e.g., apache2 or nginx) something
    needs to ensure that the uwsgi process is running. In DevStack this is done
    with systemd_. This is one of many different ways to manage uwsgi.

This document refrains from declaring a set of installation instructions for
the placement service. This is because a major point of having a WSGI
application is to make the deployment as flexible as possible. Because the
placement API service is itself stateless (all state is in the database), it is
possible to deploy as many servers as desired behind a load balancing solution
for robust and simple scaling. If you familiarize yourself with installing
generic WSGI applications (using the links in the common scenarios list,
above), those techniques will be applicable here.

.. _apache2: http://httpd.apache.org/
.. _mod_wsgi: https://modwsgi.readthedocs.io/
.. _mod_proxy_uwsgi: http://uwsgi-docs.readthedocs.io/en/latest/Apache.html
.. _nginx: http://nginx.org/
.. _uwsgi: http://uwsgi-docs.readthedocs.io/en/latest/Nginx.html
.. _gunicorn: http://gunicorn.org/
.. _first added to DevStack: https://review.opendev.org/#/c/342362/
.. _was updated: https://review.opendev.org/#/c/456717/
.. _systemd: https://review.opendev.org/#/c/448323/
.. _environment: https://docs.openstack.org/oslo.config/latest/reference/drivers.html#environment

**2. Synchronize the database**

The placement service uses its own database, defined in the
:oslo.config:group:`placement_database` section of configuration. The
:oslo.config:option:`placement_database.connection` option **must** be set or
the service will not start. The command line tool :doc:`cli/placement-manage`
can be used to migrate the database tables to their correct form, including
creating them. The database described by the ``connection`` option must already
exist and have appropriate access controls defined.

Another option for synchronization is to set
:oslo.config:option:`placement_database.sync_on_startup` to ``True`` in
configuration. This will perform any missing database migrations as the
placement web service starts. Whether you choose to sync automaticaly or use
the command line tool depends on the constraints of your environment and
deployment tooling.

.. warning:: In the Stein release, the placement code was extracted from nova.
             If you are upgrading to use the extracted placement you will need
             to migrate your placement data from the ``nova_api`` database to
             the ``placement`` database. You can find sample scripts that may
             help with this in the `placement repository`_:
             `mysql-migrate-db.sh`_ and `postgresql-migrate-db.sh`_.
             See also :ref:`placement-upgrade-notes`, below.

.. note:: Upgrading to the extracted placement at the same time as the other
          OpenStack services when upgrading to Stein is an option but *is not
          required*. The nova code will continue to have a copy of the
          placement service in its Stein release. However this copy **will** be
          deleted in Train and switching to the extracted version before
          upgrading to Train (potentially with the help of the scripts above)
          will be required.

**3. Create accounts and update the service catalog**

Create a **placement** service user with an **admin** role in Keystone.

The placement API is a separate service and thus should be registered under
a **placement** service type in the service catalog. Clients of placement, such
as the resource tracker in the nova-compute node, will use the service catalog
to find the placement endpoint.

See :ref:`configure-endpoints-pypi` for examples of creating the service user
and catalog entries.

Devstack sets up the placement service on the default HTTP port (80) with a
``/placement`` prefix instead of using an independent port.

.. _placement-upgrade-notes:

Upgrade Notes
=============

The following sub-sections provide notes on upgrading to a given target release.

.. note::

   As a reminder, the
   :ref:`placement-status upgrade check <placement-status-checks>` tool can be
   used to help determine the status of your deployment and how ready it is to
   perform an upgrade.

For releases prior to Stein, please see the `nova upgrade notes`_.

.. _nova upgrade notes: https://docs.openstack.org/nova/rocky/user/placement.html#upgrade-notes


Stein (1.0.0)
~~~~~~~~~~~~~~

If you are upgrading an existing OpenStack installation from Rocky to Stein,
and wish to use the newly extracted placement, you will need to copy some
data and configuration settings from nova. See :doc:`upgrade/to-stein` for
details of one way to manage this. The overview is:

* Configuration and policy files are, by default, located in
  ``/etc/placement``.
* The placement server side settings in ``nova.conf`` should be moved to a
  separate placement configuration file ``placement.conf``.
* The default configuration value of ``[placement]/policy_file`` is changed
  from ``placement-policy.yaml`` to ``policy.yaml``
* Several tables in the ``nova_api`` database need to be migrated to a new
  ``placement`` database.

Following these steps will ensure that future changes to placement
configuration and code will not conflict with your setup.

As stated above, using the extracted placement code is not required in Stein,
there is a copy in the Stein release of Nova. However that code will be deleted
in the Train cycle so you must upgrade to external Placement prior to
upgrading to Train.

.. _placement repository: https://opendev.org/openstack/placement
.. _mysql-migrate-db.sh: https://opendev.org/openstack/placement/raw/branch/master/tools/mysql-migrate-db.sh
.. _postgresql-migrate-db.sh: https://opendev.org/openstack/placement/raw/branch/master/tools/postgresql-migrate-db.sh


REST API
========

The placement API service provides a well-documented, JSON-based `HTTP API`_
and data model. It is designed to be easy to use from whatever HTTP client is
suitable. There is a plugin to the openstackclient_ command line tool called
osc-placement_ which is useful for occasional inspection and manipulation of
the resources in the placement service.

.. _HTTP API: https://docs.openstack.org/api-ref/placement/
.. _openstackclient: https://pypi.org/project/openstackclient/
.. _osc-placement: https://pypi.org/project/osc-placement/

Microversions
~~~~~~~~~~~~~

The placement API uses microversions for making incremental changes to the
API which client requests must opt into.

It is especially important to keep in mind that nova-compute is a client of
the placement REST API and based on how Nova supports rolling upgrades the
nova-compute service could be Newton level code making requests to an Ocata
placement API, and vice-versa, an Ocata compute service in a cells v2 cell
could be making requests to a Newton placement API.

This history of placement microversions may be found in
:doc:`placement-api-microversion-history`.


.. # NOTE(mriedem): This is the section where we hide things that we don't
   # actually want in the table of contents but sphinx build would fail if
   # they aren't in the toctree somewhere. For example, we hide api/autoindex
   # since that's already covered with modindex below.
.. toctree::
   :hidden:

   cli/index
   configuration/index
   contributor/index
   install/index
   install/from-pypi
   install/install-obs
   install/install-rdo
   install/install-ubuntu
   install/verify
   placement-api-microversion-history
   specs/index
   upgrade/to-stein
   usage/index