Documentation cleanup: front page

This is the first in a series of changes to the content in
doc/source to make it more accurately reflect the current state of
placement, now that it is in its own repo.

There are small changes throughout the front page, mostly to make
it more clear and make useful stuff a bit more discoverable.

The two major changes are:

* Older (pre-stein) upgrade notes are found by linking back to
  nova's rocky documentation.
* The REST API history is moved to its own sub-page, otherwise it
  the page is overwhelming and noisy.

Close review is probably required. cdent typed this. That has

Change-Id: I66e0c7d18b253b0a5a8fdac65e30b5b3cef37db2
Chris Dent 4 years ago committed by Tetsuro Nakamura
parent ddd993de1a
commit 176524643d
  1. 185
  2. 16

@ -47,6 +47,12 @@ For an overview of some of the features provided by placement, see
For a command line reference, see :doc:`cli/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.
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.
@ -118,7 +124,8 @@ 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
@ -142,53 +149,35 @@ above), those techniques will be applicable here.
.. _first added to DevStack:
.. _was updated:
.. _systemd:
.. _environment:
**2. Synchronize the database**
In the Newton release, where the placement code is in Nova, the nova-api
database is the only deployment option for the placement API service and the
resources it manages. After upgrading the nova-api service for Newton and
running the ``nova-manage api_db sync`` command the placement tables will be
.. TODO(efried):: Get :oslo.config:option: role working below:
placement. If :oslo.config:option:`placement_database.connection` is
The placement service uses its own database, defined in the
``[placement_database]`` section of configuration. The ``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.
With the Rocky release, it has become possible to use a separate database for
placement. If `placement_database.connection` is
configured with a database connect string, that database will be used for
storing placement data. Once the database is created, the
``nova-manage api_db sync`` command will create and synchronize both the
nova api and placement tables. If ``[placement_database]/connection`` is not
set, the nova api database will be used.
In the Stein release, where the placement code is extracted, we have scripts
for the data migration from the nova-api database to the placement database.
You can find them in the extracted placement repository,
``/tools/`` and ``/tools/``.
In the Stein release, the placement code was extracted from nova. We have
scripts which can assist with migrating placement data from the nova-api
database to the placement database. You can find them in the `placement
repository`_, ``/tools/`` and
**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 as that is what the
resource tracker in the nova-compute node will use to look up the endpoint.
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.
Devstack sets up the placement service on the default HTTP port (80) with a
``/placement`` prefix instead of using an independent port.
**4. Configure and restart nova-compute services**
The nova-compute service code will begin reporting resource provider inventory
and usage information as soon as the placement API service is in place and can
respond to requests via the endpoint registered in the service catalog.
``nova.conf`` on the compute nodes must be updated in the ``[placement]``
group to contain credentials for making requests from nova-compute to the
placement-api service.
.. _placement-upgrade-notes:
Upgrade Notes
@ -203,122 +192,29 @@ The following sub-sections provide notes on upgrading to a given target release.
used to help determine the status of your deployment and how ready it is to
perform an upgrade.
Ocata (15.0.0)
* The ``nova-compute`` service will fail to start in Ocata unless the
``[placement]`` section of nova.conf on the compute is configured. As
mentioned in the deployment steps above, the Placement service should be
deployed by this point so the computes can register and start reporting
inventory and allocation information. If the computes are deployed
and configured `before` the Placement service, they will continue to try
and reconnect in a loop so that you do not need to restart the nova-compute
process to talk to the Placement service after the compute is properly
* The ``nova.scheduler.filter_scheduler.FilterScheduler`` in Ocata will
fallback to not using the Placement service as long as there are older
``nova-compute`` services running in the deployment. This allows for rolling
upgrades of the computes to not affect scheduling for the FilterScheduler.
However, the fallback mechanism will be removed in the 16.0.0 Pike release
such that the scheduler will make decisions based on the Placement service
and the resource providers (compute nodes) registered there. This means if
the computes are not reporting into Placement by Pike, build requests will
fail with **NoValidHost** errors.
* While the FilterScheduler technically depends on the Placement service
in Ocata, if you deploy the Placement service `after` you upgrade the
``nova-scheduler`` service to Ocata and restart it, things will still work.
The scheduler will gracefully handle the absence of the Placement service.
However, once all computes are upgraded, the scheduler not being able to make
requests to Placement will result in **NoValidHost** errors.
* It is currently possible to exclude the ``CoreFilter``, ``RamFilter`` and
``DiskFilter`` from the list of enabled FilterScheduler filters such that
scheduling decisions are not based on CPU, RAM or disk usage. Once all
computes are reporting into the Placement service, however, and the
FilterScheduler starts to use the Placement service for decisions, those
excluded filters are ignored and the scheduler will make requests based on
VCPU, MEMORY_MB and DISK_GB inventory. If you wish to effectively ignore
that type of resource for placement decisions, you will need to adjust the
corresponding ``cpu_allocation_ratio``, ``ram_allocation_ratio``, and/or
``disk_allocation_ratio`` configuration options to be very high values, e.g.
* Users of CellsV1 will need to deploy a placement per cell, matching
the scope and cardinality of the regular ``nova-scheduler`` process.
Pike (16.0.0)
For releases prior to Stein, please see the `nova upgrade notes`_.
* The ``nova.scheduler.filter_scheduler.FilterScheduler`` in Pike will
no longer fall back to not using the Placement Service, even if older
computes are running in the deployment.
* The FilterScheduler now requests allocation candidates from the Placement
service during scheduling. The allocation candidates information was
introduced in the Placement API 1.10 microversion, so you should upgrade the
placement service **before** the Nova scheduler service so that the scheduler
can take advantage of the allocation candidate information.
The scheduler gets the allocation candidates from the placement API and
uses those to get the compute nodes, which come from the cell(s). The
compute nodes are passed through the enabled scheduler filters and weighers.
The scheduler then iterates over this filtered and weighed list of hosts and
attempts to claim resources in the placement API for each instance in the
request. Claiming resources involves finding an allocation candidate that
contains an allocation against the selected host's UUID and asking the
placement API to allocate the requested instance resources. We continue
performing this claim request until success or we run out of allocation
candidates, resulting in a NoValidHost error.
For a move operation, such as migration, allocations are made in Placement
against both the source and destination compute node. Once the
move operation is complete, the resource tracker in the *nova-compute*
service will adjust the allocations in Placement appropriately.
For a resize to the same host, allocations are summed on the single compute
node. This could pose a problem if the compute node has limited capacity.
Since resizing to the same host is disabled by default, and generally only
used in testing, this is mentioned for completeness but should not be a
concern for production deployments.
Queens (17.0.0)
* The minimum Placement API microversion required by the *nova-scheduler*
service is ``1.17`` in order to support `Request Traits During Scheduling`_.
This means you must upgrade the placement service before upgrading any
*nova-scheduler* services to Queens.
Rocky (18.0.0)
.. _nova upgrade notes:
* The ``nova-api`` service now requires the ``[placement]`` section to be
configured in nova.conf if you are using a separate config file just for
that service. This is because the ``nova-api`` service now needs to talk
to the placement service in order to (1) delete resource provider allocations
when deleting an instance and the ``nova-compute`` service on which that
instance is running is down (2) delete a ``nova-compute`` service record via
the ``DELETE /os-services/{service_id}`` API and (3) mirror aggregate host
associations to the placement service. This change is idempotent if
``[placement]`` is not configured in ``nova-api`` but it will result in new
warnings in the logs until configured.
* As described above, before Rocky, the placement service used the nova api
database to store placement data. In Rocky, if the ``connection`` setting in
a ``[placement_database]`` group is set in configuration, that group will be
used to describe where and how placement data is stored.
Stein (19.0.0)
* The placement code is now available from `its own repository`_.
* The placement server side settings in ``nova.conf`` can be moved to a
* The placement code is now available from its own `placement repository`_.
* 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``
* Configuration and policy files are, by default, located in
.. _placement repository:
.. _`its own repository`:
The placement API service has its own `REST API`_ and data model. One
The placement API service provides a `REST API`_ and data model. One
can get a sample of the REST API via the functional test `gabbits`_.
.. _`REST API`:
@ -336,21 +232,9 @@ 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.
.. _placement-api-microversion-history:
.. include:: ../../placement/rest_api_version_history.rst
See the :doc:`Configuration Guide <configuration/index>` for information on
configuring the system, including role-based access control policy rules.
This history of placement microversions may be found in
See the :doc:`Contributor Guide <contributor/index>` for information on how to
contribute to the placement project.
.. # 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
@ -366,4 +250,5 @@ contribute to the placement project.

@ -0,0 +1,16 @@
Licensed under the Apache License, Version 2.0 (the "License"); you may
not use this file except in compliance with the License. You may obtain
a copy of the License at
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
License for the specific language governing permissions and limitations
under the License.
.. _placement-api-microversion-history:
.. include:: ../../placement/rest_api_version_history.rst