79 lines
3.2 KiB
ReStructuredText
79 lines
3.2 KiB
ReStructuredText
..
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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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Quotas
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========
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Nova uses a quota system for setting limits on resources such as number of
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instances or amount of CPU that a specific project or user can use.
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Quotas are enforced by making a claim, or reservation, on resources when a
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request is made, such as creating a new server. If the claim fails, the request
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is rejected. If the reservation succeeds then the operation progresses until
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such a point that the reservation is either converted into usage (the operation
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was successful) or rolled back (the operation failed).
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Typically the quota reservation is made in the nova-api service and the usage
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or rollback is performed in the nova-compute service, at least when dealing
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with a server creation or move operation.
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Quota limits and usage can be retrieved via the ``limits`` REST API.
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Checking quota
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==============
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When calculating limits for a given resource and tenant, the following
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checks are made in order:
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* Depending on the resource, is there a tenant-specific limit on the resource
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in either the `quotas` or `project_user_quotas` tables in the database? If
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so, use that as the limit. You can create these resources by doing::
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openstack quota set --instances 5 <project>
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* Check to see if there is a hard limit for the given resource in the
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`quota_classes` table in the database for the `default` quota class. If so,
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use that as the limit. You can modify the default quota limit for a resource
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by doing::
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openstack quota set --class --instances 5 default
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* If the above does not provide a resource limit, then rely on the ``quota_*``
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configuration options for the default limit.
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.. note:: The API sets the limit in the `quota_classes` table. Once a default
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limit is set via the `default` quota class, that takes precedence over
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any changes to that resource limit in the configuration options. In other
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words, once you've changed things via the API, you either have to keep those
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synchronized with the configuration values or remove the default limit from
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the database manually as there is no REST API for removing quota class
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values from the database.
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Known issues
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============
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TODO: talk about quotas getting out of sync and `how to recover`_
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.. _how to recover: https://specs.openstack.org/openstack/nova-specs/specs/newton/implemented/refresh-quotas-usage.html
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Future plans
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============
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TODO: talk about quotas in the `resource counting spec`_ and `nested quotas`_
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.. _resource counting spec: https://specs.openstack.org/openstack/nova-specs/specs/ocata/approved/cells-count-resources-to-check-quota-in-api.html
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.. _nested quotas: https://specs.openstack.org/openstack/nova-specs/specs/mitaka/approved/nested-quota-driver-api.html
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