Contributing new extensions to Neutron

Contributing new extensions to Neutron


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 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 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 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, 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.

Security Issues

Here are some answers to how to handle security issues in your repo, taken from this openstack-dev mailing list message:

  • How should security your issues be managed?

The OpenStack Vulnerability Management Team (VMT) follows a documented process which can basically be reused by any project-team when needed.

  • Should the OpenStack security team be involved?

The OpenStack VMT directly oversees vulnerability reporting and disclosure for a subset of OpenStack source code repositories. However, they are still quite happy to answer any questions you might have about vulnerability management for your own projects even if they’re not part of that set. Feel free to reach out to the VMT in public or in private.

Also, the VMT is an autonomous subgroup of the much larger OpenStack Security project-team. They’re a knowledgeable bunch and quite responsive if you want to get their opinions or help with security-related issues (vulnerabilities or otherwise).

  • Does a CVE need to be filed?

It can vary widely. If a commercial distribution such as Red Hat is redistributing a vulnerable version of your software, then they may assign one anyway even if you don’t request one yourself. Or the reporter may request one; the reporter may even be affiliated with an organization who has already assigned/obtained a CVE before they initiate contact with you.

  • Do the maintainers need to publish OSSN or equivalent documents?

OpenStack Security Advisories (OSSA) are official publications of the OpenStack VMT and only cover VMT-supported software. OpenStack Security Notes (OSSN) are published by editors within the OpenStack Security project-team on more general security topics and may even cover issues in non-OpenStack software commonly used in conjunction with OpenStack, so it’s at their discretion as to whether they would be able to accommodate a particular issue with an OSSN.

However, these are all fairly arbitrary labels, and what really matters in the grand scheme of things is that vulnerabilities are handled seriously, fixed with due urgency and care, and announced widely – not just on relevant OpenStack mailing lists but also preferably somewhere with broader distribution like the Open Source Security mailing list. The goal is to get information on your vulnerabilities, mitigating measures and fixes into the hands of the people using your software in a timely manner.

  • Anything else to consider here?

The OpenStack VMT is in the process of trying to reinvent itself so that it can better scale within the context of the “Big Tent.” This includes making sure the policy/process documentation is more consumable and reusable even by project-teams working on software outside the scope of our charter. It’s a work in progress, and any input is welcome on how we can make this function well for everyone.

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

Project Initial Setup

The how-to below assumes that the third-party library will be hosted on 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 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 repo or any publicly available git repo, e.g. This would be a temporary buffer to be used to feed the one on
  • 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 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,, etc.).
  • Create a repository on 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 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 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)


  • Each subproject repository should have its own oslo.i18n integration wrapper module ${MODULE_NAME}/ The detail is found at


    DOMAIN name should match your module name ${MODULE_NAME}.

  • Import _() from your ${MODULE_NAME}/


    Do not use _() in the builtins namespace which is registered by gettext.install() in neutron/ It is now deprecated as described in oslo.18n documentation.

Setting up translation support

You need to create or edit the following files to start translation support:

  • setup.cfg
  • babel.cfg

We have a good example for an oslo project at

Add the following to setup.cfg:

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

directory = ${MODULE_NAME}/locale
domain = ${MODULE_NAME}

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

Note that ${MODULE_NAME} is used in all names.

Create babel.cfg with the following contents:

[python: **.py]

Enable Translation

To update and import translations, you need to make a change in project-config. A good example is found at After doing this, the necessary jobs will be run and push/pull a message catalog to/from the translation infrastructure.

Integrating with the Neutron system

Configuration Files

The data_files in the [files] section of setup.cfg of Neutron shall not contain any third-party references. These shall be located in the same section of the third-party repo’s own setup.cfg file.

  • Note: Care should be taken when naming sections in configuration files. When the Neutron service or an agent starts, oslo.config loads sections from all specified config files. This means that if a section [foo] exists in multiple config files, duplicate settings will collide. It is therefore recommended to prefix section names with a third-party string, e.g. [vendor_foo].

Since Mitaka, configuration files are not maintained in the git repository but should be generated as follows:

``tox -e genconfig``

If a ‘tox’ environment is unavailable, then you can run the following script instead to generate the configuration files:


It is advised that subprojects do not keep their configuration files in their respective trees and instead generate them using a similar approach as Neutron does.

ToDo: Inclusion in OpenStack documentation?
Is there a recommended way to have third-party config options listed in the configuration guide in

Database Models and Migrations

A third-party repo may contain database models for its own tables. Although these tables are in the Neutron database, they are independently managed entirely within the third-party code. Third-party code shall never modify neutron core tables in any way.

Each repo has its own expand and contract alembic migration branches. A third-party repo’s alembic migration branches may operate only on tables that are owned by the repo.

  • Note: Care should be taken when adding new tables. To prevent collision of table names it is required to prefix them with a vendor/plugin string.
  • Note: A third-party maintainer may opt to use a separate database for their tables. This may complicate cases where there are foreign key constraints across schemas for DBMS that do not support this well. Third-party maintainer discretion advised.

The database tables owned by a third-party repo can have references to fields in neutron core tables. However, the alembic branch for a plugin/driver repo shall never update any part of a table that it does not own.

Note: What happens when a referenced item changes?

  • Q: If a driver’s table has a reference (for example a foreign key) to a neutron core table, and the referenced item is changed in neutron, what should you do?
  • A: Fortunately, this should be an extremely rare occurrence. Neutron core reviewers will not allow such a change unless there is a very carefully thought-out design decision behind it. That design will include how to address any third-party code affected. (This is another good reason why you should stay actively involved with the Neutron developer community.)

The neutron-db-manage alembic wrapper script for neutron detects alembic branches for installed third-party repos, and the upgrade command automatically applies to all of them. A third-party repo must register its alembic migrations at installation time. This is done by providing an entrypoint in setup.cfg as follows:

For a third-party repo named networking-foo, add the alembic_migrations directory as an entrypoint in the neutron.db.alembic_migrations group:

neutron.db.alembic_migrations =
    networking-foo = networking_foo.db.migration:alembic_migrations
ToDo: neutron-db-manage autogenerate
The alembic autogenerate command needs to support branches in external repos. Bug #1471333 has been filed for this.

DB Model/Migration Testing

Here is a template functional test third-party maintainers can use to develop tests for model-vs-migration sync in their repos. It is recommended that each third-party CI sets up such a test, and runs it regularly against Neutron master.

Entry Points

The Python setuptools installs all entry points for packages in one global namespace for an environment. Thus each third-party repo can define its package’s own [entry_points] in its own setup.cfg file.

For example, for the networking-foo repo:

console_scripts =
    neutron-foo-agent =
neutron.core_plugins =
    foo_monolithic = networking_foo.plugins.monolithic.plugin:FooPluginV2
neutron.service_plugins =
    foo_l3 =
neutron.ml2.type_drivers =
    foo_type =
neutron.ml2.mechanism_drivers =
    foo_ml2 =
neutron.ml2.extension_drivers =
    foo_ext =
  • Note: It is advisable to include foo in the names of these entry points to avoid conflicts with other third-party packages that may get installed in the same environment.

API Extensions

Extensions can be loaded in two ways:

  1. Use the append_api_extensions_path() library API. This method is defined in neutron/api/ in the neutron tree.
  2. Leverage the api_extensions_path config variable when deploying. See the example config file etc/neutron.conf in the neutron tree where this variable is commented.

Service Providers

If your project uses service provider(s) the same way VPNAAS and LBAAS do, you specify your service provider in your project_name.conf file like so:

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

In order for Neutron to load this correctly, make sure you do the following in your code:

from neutron.db import servicetype_db
service_type_manager = servicetype_db.ServiceTypeManager.get_instance()

This is typically required when you instantiate your service plugin class.

Interface Drivers

Interface (VIF) drivers for the reference implementations are defined in neutron/agent/linux/ Third-party interface drivers shall be defined in a similar location within their own repo.

The entry point for the interface driver is a Neutron config option. It is up to the installer to configure this item in the [default] section. For example:

interface_driver = networking_foo.agent.linux.interface.FooInterfaceDriver
ToDo: Interface Driver port bindings.
VIF_TYPE_* constants in neutron_lib/api/definitions/ should be moved from neutron core to the repositories where their drivers are implemented. We need to provide some config or hook mechanism for VIF types to be registered by external interface drivers. For Nova, selecting the VIF driver can be done outside of Neutron (using the new os-vif python library?). Armando and Akihiro to discuss.

Rootwrap Filters

If a third-party repo needs a rootwrap filter for a command that is not used by Neutron core, then the filter shall be defined in the third-party repo.

For example, to add a rootwrap filters for commands in repo networking-foo:

  • In the repo, create the file: etc/neutron/rootwrap.d/foo.filters

  • In the repo’s setup.cfg add the filters to data_files:

    data_files =
        etc/neutron/rootwrap.d =

Extending python-neutronclient

The maintainer of a third-party component may wish to add extensions to the Neutron CLI client. Thanks to this can now be accomplished. See Client Command Extensions.

Other repo-split items

(These are still TBD.)

  • Splitting policy.json? ToDo Armando will investigate.
  • Generic instructions (or a template) for installing an out-of-tree plugin or driver for Neutron. Possibly something for the networking guide, and/or a template that plugin/driver maintainers can modify and include with their package.
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