x/group-based-policy-specs
Code Issues Proposed changes
group-based-policy-specs/specs/juno/gbp-extension-drivers.rst
Igor Duarte Cardoso de694f7164 tox doesn't fail anymore at the py27 environment 
This patch fixes existing specs to totally conform to tox py27 environment
tests as specified by tests/test_titles.py. Semantic information of all
existing specs has not been changed.

Specifically, this patch makes the following changes:
* Fixes all titles and subtitles' capitalization inconsistencies:
  defaulting to only having the first word being capitalized (this seems
  to be the general rule in group-based-policy-specs);
* Adds missing titles and subtitles to some specs;
* Changes tests/test_titles.py for consistency: only 1st word capitalized;
* Changes tests/tests_titles.py: subtitle count inside Testing or
  Documentation impact no longer restricted to 0.

Change-Id: I88e30b0825f5279a8c6808fd9a2fc2987b6611f9
Closes-Bug: #1437282
2015-04-15 10:44:25 +01:00

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This work is licensed under a Creative Commons Attribution 3.0 Unported
License.
http://creativecommons.org/licenses/by/3.0/legalcode
==========================================
GBP Extension Drivers
==========================================
Launchpad blueprint:
https://blueprints.launchpad.net/group-based-policy/+spec/gbp-extension-drivers
The existing group-policy-mapping extension makes assumptions that are
not valid for all GBP policy drivers. Also, certain policy drivers may
need to extend the GBP API to enable capabilities not common to all
policy drivers. To address both these issues, this blueprint adds an
extension driver framework to GBP, and re-factors the
group-policy-mapping extension as an optional driver within this
framework.
Problem description
===================
Currently, both the group-policy and group-policy-mapping extensions
are hardwired into the GBP plugin implementation. The group-policy
extension defines the core GBP API resources, while the
group-policy-mapping extension adds attributes to these resources
exposing a specific mapping from the GBP resources to Neutron
resources. Since GBP policy drivers are likely to vary in whether and
how they map GBP resources to Neutron resources, the set of attributes
defined in the group-policy-mapping extension are not likely to all be
meaningful for all policy drivers. Additional mapping attributes may
be also needed.
Also, there is currently no way to extend GBP resource APIs with
attributes enabling capabilities that are not common to all policy
drivers, without building those attributes into the GBP service plugin
itself.
Proposed change
===============
First, the extension driver framework from ML2 will be ported to GBP,
allowing GBP resources to be extended with additional attributes. An
ExtensionDriver abstract base class will be added to the
group_policy_driver_api module with the following methods and
properties:
* initialize(self) - Perform driver initialization.
* extension_alias(self) - Supported extension alias.
* process_create_<resource>(self, session, data, result) - Process
extended attributes for <resource> creation.
* process_update_<resource>(self, session, data, result) - Process
extended attributes for <resource> update.
* extend_<resource>_dict(self, session, result) - Add extended
attributes to <resource> dictionary.
See the ML2 extension driver specification and code review listed
below in the references for more details.
Then GBP's current mapping extension will be re-factored as a driver
within this framework, allowing the GBP plugin to be configured with
or without this extension, or with additional or alternative resource
mapping extensions.
Either as part of this blueprint or as a follow-on blueprint, the
existing group-policy-mapping extension may be split into a
group-policy-base-mapping extension that defines only the mapping from
policy target to port, and a separate extension that defines the
remainder of the mapping exposed by the resource_mapping policy
driver.
Alternatives
------------
The alternatives considered include:
* Don't change anything in the GBP service plugin. Individual policy
drivers can chose whether to allow each group-policy-mapping
attribute to be set during create and update operations or to raise
an exception when the attribute value is supplied. If they don't use
or want to expose a specific group-policy-mapping attribute, they
can avoid setting any value for it in the DB. No additional GBP API
extensions are possible.
* As above, but remove attributes from the group-policy-mapping
extension that are not applicable to most or all policy
drivers. Most likely, only the mapping for policy target to Neutron
port would remain.
Data model impact
-----------------
Adding the extension driver framework has no direct data model
impact. Extension drivers implemented within the framework each have
their own data models.
Re-factoring the existing group-policy-mapping extension as an
extension driver should not by itself require structural changes to
the data model currently defined in group_policy_mapping_db.py. But
making the mapping attributes optional may require using separate
tables instead of extending the existing group-policy tables as is
currently done. Since we don't yet support upgrades between GBP
releases, existing DB migrations will be modified as necessary.
REST API impact
---------------
The group-policy-mapping extension is no longer built into the GBP
service plugin, and therefore may not always be available as part of
its REST API. This blueprint itself does not require any specific REST
API changes.
Security impact
---------------
This blueprint has no security impact.
Notifications impact
--------------------
This blueprint has no impact on notifications.
Other end user impact
---------------------
The python client will need to handle the possibility that different
extensions are available based on which extension drivers are
configured.
Performance impact
------------------
This blueprint should have minimal impact on performance. The GBP
service plugin will make calls on the registered extension drivers
during all REST operations. The group-policy-mapping extension
attributes that are now implemented within the same tables as the GBP
resources will be moved to separate tables.
Other deployer impact
---------------------
A new extension_drivers configuration variable will need to be set to
enable any extensions required driver(s) specified in the
policy_drivers configuration variable.
Developer impact
----------------
Developers of policy drivers will now be able to define any needed
extensions to the GBP API by defining extension drivers.
Implementation
==============
Assignee(s)
-----------
Primary assignee:
rkukura
Other contributors:
None
Work items
----------
* Port extension driver API and unit tests from ML2 to GBP, with
support for extending the policy target, policy target group, l2
policy, and l3 policy resources.
* Re-factor the group-policy-mapping extension as an extension driver.
* Possibly add support for extending additional resource.
* Possibly split the group-policy-mapping extension into two separate
extensions implemented by corresponding drivers.
Dependencies
============
* This blueprint enables
https://blueprints.launchpad.net/openstack/?searchtext=mapping-extension-refactor.
Testing
=======
New unit tests will be added for the extension driver framework
itself, and existing unit tests for the mapping will be updated to
configure the required extension driver(s).
Documentation impact
====================
Eventual GBP documentation will need to address configuring extension
drivers and the fact that different policy drivers may require
different API extensions.
References
==========
* ML2 extension driver blueprint:
https://blueprints.launchpad.net/neutron/+spec/extensions-in-ml2
* ML2 extension driver specification:
http://git.openstack.org/cgit/openstack/neutron-specs/tree/specs/juno/neutron-ml2-mechanismdriver-extensions.rst
* ML2 extension driver code review: https://review.openstack.org/#/c/89211/
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