Contributing new extensions to Neutron¶

Introduction¶

Neutron has a pluggable architecture, with a number of extension points. This documentation covers aspects relevant to contributing new Neutron v2 core (aka monolithic) plugins, ML2 mechanism drivers, and L3 service plugins. This document will initially cover a number of process-oriented aspects of the contribution process, and proceed to provide a how-to guide that shows how to go from 0 LOC’s to successfully contributing new extensions to Neutron. In the remainder of this guide, we will try to use practical examples as much as we can so that people have working solutions they can start from.

This guide is for a developer who wants to have a degree of visibility within the OpenStack Networking project. If you are a developer who wants to provide a Neutron-based solution without interacting with the Neutron community, you are free to do so, but you can stop reading now, as this guide is not for you.

Plugins and drivers for non-reference implementations are known as “third-party” code. This includes code for supporting vendor products, as well as code for supporting open-source networking implementations.

Before the Kilo release these plugins and drivers were included in the Neutron tree. During the Kilo cycle the third-party plugins and drivers underwent the first phase of a process called decomposition. During this phase, each plugin and driver moved the bulk of its logic to a separate git repository, while leaving a thin “shim” in the neutron tree together with the DB models and migrations (and perhaps some config examples).

During the Liberty cycle the decomposition concept was taken to its conclusion by allowing third-party code to exist entirely out of tree. Further extension mechanisms have been provided to better support external plugins and drivers that alter the API and/or the data model.

In the Mitaka cycle we will require all third-party code to be moved out of the neutron tree completely.

‘Outside the tree’ can be anything that is publicly available: it may be a repo on git.openstack.org for instance, a tarball, a pypi package, etc. A plugin/drivers maintainer team self-governs in order to promote sharing, reuse, innovation, and release of the ‘out-of-tree’ deliverable. It should not be required for any member of the core team to be involved with this process, although core members of the Neutron team can participate in whichever capacity is deemed necessary to facilitate out-of-tree development.

This guide is aimed at you as the maintainer of code that integrates with Neutron but resides in a separate repository.

Contribution Process¶

If you want to extend OpenStack Networking with your technology, and you want to do it within the visibility of the OpenStack project, follow the guidelines and examples below. We’ll describe best practices for:

• Design and Development;
• Testing and Continuous Integration;
• Defect Management;
• Backport Management for plugin specific code;
• DevStack Integration;
• Documentation;

Once you have everything in place you may want to add your project to the list of Neutron sub-projects. See Adding or removing projects to the stadium for details.

Design and Development¶

Assuming you have a working repository, any development to your own repo does not need any blueprint, specification or bugs against Neutron. However, if your project is a part of the Neutron Stadium effort, you are expected to participate in the principles of the Four Opens, meaning your design should be done in the open. Thus, it is encouraged to file documentation for changes in your own repository.

If your code is hosted on git.openstack.org then the gerrit review system is automatically provided. Contributors should follow the review guidelines similar to those of Neutron. However, you as the maintainer have the flexibility to choose who can approve/merge changes in your own repo.

It is recommended (but not required, see policies) that you set up a third-party CI system. This will provide a vehicle for checking the third-party code against Neutron changes. See Testing and Continuous Integration below for more detailed recommendations.

Design documents can still be supplied in form of Restructured Text (RST) documents, within the same third-party library repo. If changes to the common Neutron code are required, an RFE may need to be filed. However, every case is different and you are invited to seek guidance from Neutron core reviewers about what steps to follow.

Testing and Continuous Integration¶

The following strategies are recommendations only, since third-party CI testing is not an enforced requirement. However, these strategies are employed by the majority of the plugin/driver contributors that actively participate in the Neutron development community, since they have learned from experience how quickly their code can fall out of sync with the rapidly changing Neutron core code base.

• You should run unit tests in your own external library (e.g. on git.openstack.org where Jenkins setup is for free).

• Your third-party CI should validate third-party integration with Neutron via functional testing. The third-party CI is a communication mechanism. The objective of this mechanism is as follows:

  • it communicates to you when someone has contributed a change that potentially breaks your code. It is then up to you maintaining the affected plugin/driver to determine whether the failure is transient or real, and resolve the problem if it is.
  • it communicates to a patch author that they may be breaking a plugin/driver. If they have the time/energy/relationship with the maintainer of the plugin/driver in question, then they can (at their discretion) work to resolve the breakage.
  • it communicates to the community at large whether a given plugin/driver is being actively maintained.
  • A maintainer that is perceived to be responsive to failures in their third-party CI jobs is likely to generate community goodwill.

  It is worth noting that if the plugin/driver repository is hosted on git.openstack.org, due to current openstack-infra limitations, it is not possible to have third-party CI systems participating in the gate pipeline for the repo. This means that the only validation provided during the merge process to the repo is through unit tests. Post-merge hooks can still be exploited to provide third-party CI feedback, and alert you of potential issues. As mentioned above, third-party CI systems will continue to validate Neutron core commits. This will allow them to detect when incompatible changes occur, whether they are in Neutron or in the third-party repo.

Defect Management¶

Bugs affecting third-party code should not be filed in the Neutron project on launchpad. Bug tracking can be done in any system you choose, but by creating a third-party project in launchpad, bugs that affect both Neutron and your code can be more easily tracked using launchpad’s “also affects project” feature.

Backport Management Strategies¶

This section applies only to third-party maintainers who had code in the Neutron tree during the Kilo and earlier releases. It will be obsolete once the Kilo release is no longer supported.

If a change made to out-of-tree third-party code needs to be back-ported to in-tree code in a stable branch, you may submit a review without a corresponding master branch change. The change will be evaluated by core reviewers for stable branches to ensure that the backport is justified and that it does not affect Neutron core code stability.

DevStack Integration Strategies¶

When developing and testing a new or existing plugin or driver, the aid provided by DevStack is incredibly valuable: DevStack can help get all the software bits installed, and configured correctly, and more importantly in a predictable way. For DevStack integration there are a few options available, and they may or may not make sense depending on whether you are contributing a new or existing plugin or driver.

If you are contributing a new plugin, the approach to choose should be based on Extras.d Hooks’ externally hosted plugins. With the extra.d hooks, the DevStack integration is co-located with the third-party integration library, and it leads to the greatest level of flexibility when dealing with DevStack based dev/test deployments.

One final consideration is worth making for third-party CI setups: if Devstack Gate is used, it does provide hook functions that can be executed at specific times of the devstack-gate-wrap script run. For example, the Neutron Functional job uses them. For more details see devstack-vm-gate-wrap.sh.

Project Initial Setup¶

The how-to below assumes that the third-party library will be hosted on git.openstack.org. This lets you tap in the entire OpenStack CI infrastructure and can be a great place to start from to contribute your new or existing driver/plugin. The list of steps below are summarized version of what you can find on http://docs.openstack.org/infra/manual/creators.html. They are meant to be the bare minimum you have to complete in order to get you off the ground.

• Create a public repository: this can be a personal git.openstack.org repo or any publicly available git repo, e.g. https://github.com/john-doe/foo.git. This would be a temporary buffer to be used to feed the one on git.openstack.org.
• Initialize the repository: if you are starting afresh, you may optionally want to use cookiecutter to get a skeleton project. You can learn how to use cookiecutter on https://git.openstack.org/cgit/openstack-dev/cookiecutter. If you want to build the repository from an existing Neutron module, you may want to skip this step now, build the history first (next step), and come back here to initialize the remainder of the repository with other files being generated by the cookiecutter (like tox.ini, setup.cfg, setup.py, etc.).
• Create a repository on git.openstack.org. For this you need the help of the OpenStack infra team. It is worth noting that you only get one shot at creating the repository on git.openstack.org. This is the time you get to choose whether you want to start from a clean slate, or you want to import the repo created during the previous step. In the latter case, you can do so by specifying the upstream section for your project in project-config/gerrit/project.yaml. Steps are documented on the Repository Creator’s Guide.
• Ask for a Launchpad user to be assigned to the core team created. Steps are documented in this section.
• Fix, fix, fix: at this point you have an external base to work on. You can develop against the new git.openstack.org project, the same way you work with any other OpenStack project: you have pep8, docs, and python27 CI jobs that validate your patches when posted to Gerrit. For instance, one thing you would need to do is to define an entry point for your plugin or driver in your own setup.cfg similarly as to how it is done in the setup.cfg for ODL.
• Define an entry point for your plugin or driver in setup.cfg
• Create third-party CI account: if you do not already have one, follow instructions for third-party CI to get one.

Internationalization support¶

OpenStack is committed to broad international support. Internationalization (I18n) is one of important areas to make OpenStack ubiquitous. Each project is recommended to support i18n.

This section describes how to set up translation support. The description in this section uses the following variables:

• repository : openstack/${REPOSITORY} (e.g., openstack/networking-foo)
• top level python path : ${MODULE_NAME} (e.g., networking_foo)

[extract_messages]
keywords = _ gettext ngettext l_ lazy_gettext
mapping_file = babel.cfg
output_file = ${MODULE_NAME}/locale/${MODULE_NAME}.pot

[compile_catalog]
directory = ${MODULE_NAME}/locale
domain = ${MODULE_NAME}

[update_catalog]
domain = ${MODULE_NAME}
output_dir = ${MODULE_NAME}/locale
input_file = ${MODULE_NAME}/locale/${MODULE_NAME}.pot

[python: **.py]

Integrating with the Neutron system¶

``tox -e genconfig``

./tools/generate_config_file_samples.sh

[entry_points]
neutron.db.alembic_migrations =
    networking-foo = networking_foo.db.migration:alembic_migrations

[entry_points]
console_scripts =
    neutron-foo-agent = networking_foo.cmd.eventlet.agents.foo:main
neutron.core_plugins =
    foo_monolithic = networking_foo.plugins.monolithic.plugin:FooPluginV2
neutron.service_plugins =
    foo_l3 = networking_foo.services.l3_router.l3_foo:FooL3ServicePlugin
neutron.ml2.type_drivers =
    foo_type = networking_foo.plugins.ml2.drivers.foo:FooType
neutron.ml2.mechanism_drivers =
    foo_ml2 = networking_foo.plugins.ml2.drivers.foo:FooDriver
neutron.ml2.extension_drivers =
    foo_ext = networking_foo.plugins.ml2.drivers.foo:FooExtensionDriver

[service_providers]
# Must be in form:
# service_provider=<service_type>:<name>:<driver>[:default][,...]

from neutron.db import servicetype_db
service_type_manager = servicetype_db.ServiceTypeManager.get_instance()
service_type_manager.add_provider_configuration(
    YOUR_SERVICE_TYPE,
    pconf.ProviderConfiguration(YOUR_SERVICE_MODULE))

[default]
interface_driver = networking_foo.agent.linux.interface.FooInterfaceDriver