x
/
group-based-policy-specs
Code Issues Proposed changes
group-based-policy-specs/specs/juno/gbp-extension-drivers.rst

7.0 KiB
Raw Blame History

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

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