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* 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 * Use maxdepth of 1 * Rename a few sections with what are hopefully better names The next step is to prune out outdated documents and further cleanup this page.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
58 lines
1.5 KiB
ReStructuredText
58 lines
1.5 KiB
ReStructuredText
Hooks
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=====
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Hooks provide a mechanism to extend Nova with custom code through a plugin
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mechanism.
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Named hooks are added to nova code via a decorator that will lazily load
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plugin code matching the name. The loading works via setuptools
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`entry points`_.
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.. _`entry points`: http://pythonhosted.org/setuptools/pkg_resources.html#entry-points
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What are hooks good for?
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------------------------
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Hooks are good for anchoring your custom code to Nova internal APIs.
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What are hooks NOT good for?
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----------------------------
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Hooks should not be used when API stability is a key factor. Internal APIs may
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change. Consider using a notification driver if this is important to you.
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Declaring hooks in the Nova codebase
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------------------------------------
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The following example declares a *resize_hook* around the *resize_instance* method::
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from nova import hooks
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@hooks.add_hook("resize_hook")
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def resize_instance(self, context, instance, a=1, b=2):
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...
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Hook objects can now be attached via entry points to the *resize_hook*.
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Adding hook object code
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-----------------------
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1. Setup a Python package with a setup.py file.
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2. Add the following to the setup.py setup call::
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entry_points = {
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'nova.hooks': [
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'resize_hook=your_package.hooks:YourHookClass',
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]
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},
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3. *YourHookClass* should be an object with *pre* and/or *post* methods::
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class YourHookClass(object):
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def pre(self, *args, **kwargs):
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....
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def post(self, rv, *args, **kwargs):
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....
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