56 lines
2.4 KiB
ReStructuredText
56 lines
2.4 KiB
ReStructuredText
..
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Copyright 2010-2011 United States Government as represented by the
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Administrator of the National Aeronautics and Space Administration.
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All Rights Reserved.
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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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.. _service_manager_driver:
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Services, Managers and Drivers
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==============================
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The responsibilities of Services, Managers, and Drivers, can be a bit confusing to people that are new to nova. This document attempts to outline the division of responsibilities to make understanding the system a little bit easier.
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Currently, Managers and Drivers are specified by flags and loaded using utils.load_object(). This method allows for them to be implemented as singletons, classes, modules or objects. As long as the path specified by the flag leads to an object (or a callable that returns an object) that responds to getattr, it should work as a manager or driver.
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The :mod:`nova.service` Module
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------------------------------
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.. automodule:: nova.service
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:noindex:
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:members:
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:undoc-members:
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:show-inheritance:
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The :mod:`nova.manager` Module
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------------------------------
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.. automodule:: nova.manager
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:noindex:
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:members:
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:undoc-members:
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:show-inheritance:
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Implementation-Specific Drivers
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-------------------------------
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A manager will generally load a driver for some of its tasks. The driver is responsible for specific implementation details. Anything running shell commands on a host, or dealing with other non-python code should probably be happening in a driver.
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Drivers should minimize touching the database, although it is currently acceptable for implementation specific data. This may be reconsidered at some point.
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It usually makes sense to define an Abstract Base Class for the specific driver (i.e. VolumeDriver), to define the methods that a different driver would need to implement.
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