nova/doc/source/services.rst
Joe Gordon a1e8fc6dd9 Update docs layout
* Explain these docs are for trunk (copied from ironic)
* All the docs in this repo are meant to be developer docs, so having a
  devref inside of the docs is redundant and just makes the docs more
  complicated to navigate. Move everything out of the devref folder and
  link to everything from main index.
* Move man pages into separate section. The man pages are pretty sparse
* right now, we should either make them useful or just delete them
* Remove dead docs from unused_docs list in doc/source/conf.py
* Shuffle docs landing page, move common referees to the top (API,
  hypervisor support matrix), Add a introduction section and more. The
  hope is the updated layout makes this document easier to navigate.
* Use maxdepth of 1
* Rename a few sections with what are hopefully better names

The next step is to prune out outdated documents and further cleanup
this page.

Change-Id: Iff453e47ccc902a0e72b1a5f6ce1ee939ff3a1a0
2015-05-15 10:47:18 -07:00

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..
Copyright 2010-2011 United States Government as represented by the
Administrator of the National Aeronautics and Space Administration.
All Rights Reserved.
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
http://www.apache.org/licenses/LICENSE-2.0
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.
.. _service_manager_driver:
Services, Managers and Drivers
==============================
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.
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.
The :mod:`nova.service` Module
------------------------------
.. automodule:: nova.service
:noindex:
:members:
:undoc-members:
:show-inheritance:
The :mod:`nova.manager` Module
------------------------------
.. automodule:: nova.manager
:noindex:
:members:
:undoc-members:
:show-inheritance:
Implementation-Specific Drivers
-------------------------------
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.
Drivers should minimize touching the database, although it is currently acceptable for implementation specific data. This may be reconsidered at some point.
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.