If you would like to contribute to the development of OpenStack, you must follow the steps in this page:

If you already have a good understanding of how the system works and your OpenStack accounts are set up, you can skip to the development workflow section of this documentation to learn how changes to OpenStack should be submitted for review via the Gerrit tool:

Pull requests submitted through GitHub will be ignored.

Bugs should be filed on Launchpad, not GitHub:

As your code is subject to the review guidelines, please take the time to familiarize yourself with those guidelines.

Rehoming Existing Code

The checklist below aims to provide guidance for developers rehoming (moving) code into neutron-lib. Rehoming approaches that fall outside the scope herein will need to be considered on a case by case basis.

The rehoming workflow procedure has four main phases:

  1. Phase 1: Rehome the code from neutron into neutron-lib.
  2. Phase 2: Enhance the code in neutron-lib if necessary.
  3. Phase 3: Release neutron-lib with the code so consumers can use it.
  4. Phase 4: Consume by removing the rehomed code from its source and changing references to use neutron-lib.

Phase 1: Rehome

  1. Identify the chunk of code for rehoming. Applicable code includes common classes/functions/modules/etc. that are consumed by networking project(s) outside of neutron. Optimal consumption patterns of the code at hand must also be considered to ensure the rehomed code addresses any technical debt. Finally, leave low-hanging fruit for last and tackle the most commonly used code first. If you have any doubt about the applicability of code for rehoming, reach out to one of the neutron core developers before digging in.
  2. Find and identify any unit tests for the code being rehomed. These unit tests can often be moved into neutron-lib with minimal effort. After inspecting the applicable unit tests, rewrite any that are non-optimal.
  3. Search and understand the consumers of the code being rehomed. This must include other networking projects in addition to neutron itself. At this point it may be determined that the code should be refactored before it is consumed. There are a few common strategies for refactoring, and the one chosen will depend on the nature of the code at hand:
    • Refactor/enhance the code as part of the initial neutron-lib patch. If this change will be disruptive to consumers, clearly communicate the change via email list or meeting topic.
    • Leave the refactoring to the next (Enhance) phase. In this rehome phase, copy the code as-is into a private module according to our conventions. This approach is slower, but may be necessary in some cases.
  4. Understand existing work underway which may impact the rehomed code, for example, in-flight patch sets that update the code being rehomed. In some cases it may make sense to let the in-flight patch merge and solidify a bit before rehoming.
  5. Prepare the code for neutron-lib. This may require replacing existing imports with those provided by neutron-lib and/or rewriting/rearchitecting non-optimal code (see above). The interfaces in the rehomed code are subject to our conventions.
  6. Prepare the unit test code for neutron-lib. As indicated in the review guidelines we are looking for a high code coverage by tests. This may require adding additional tests if neutron was lacking in coverage.
  7. Submit and shepherd your patch through its neutron-lib review. Include a release note that describes the code’s old neutron location and new neutron-lib location. Also note that in some cases it makes sense to prototype a change in a consumer project to better understand the impacts of the change, which can be done using the Depends-On: approach described in the review guidelines


  • 319769 brought over a number of common utility functions as-is from neutron into a new package structure within neutron-lib.
  • 253661 rehomed neutron callbacks into a private package that’s enhanced via 346554.
  • 319386 rehomes a validator from neutron into neutron-lib.

Phase 2: Enhance

If the rehomed code is not applicable for enhancements and wasn’t made private in Phase 1, you can skip this step.

Develop and shepherd the enhancements to the private rehomed code applicable at this time. Private APIs made public as part of this phase will also need release notes indicating the new public functionality.


  • 346554 enhances the rehomed private callback API in neutron-lib.

Phase 3: Release

A new neutron-lib release can be cut at any time. You can also request a release by following the README instructions in the openstack/releases project.

Once a release is cut, an openstack infra proposal bot will submit patches to the master branch of all projects that consume neutron-lib to set the new release as the minimum requirement. Someone from the neutron release team can bump global requirements (g-r); for example review 393600.

When the bot-proposed requirement patches have merged, your rehomed code can be consumed.

Phase 4: Consume

It’s critical that before you submit your patch to remove the rehomed code from its source that you perform a diff between it and the rehomed version in neutron-lib to ensure nothing has changed in the source. If something has changed in the source, you need to push and shepherd a patch to neutron-lib with the difference(s) before proceeding with this consumption phase.

The following guidelines are intended to provide a smooth transition to the rehomed code in neutron-lib and minimize impacts to subprojects consuming the rehomed code from its source.

  • If the change to consume the code from neutron-lib is widespread and/or “important”, introduce your intentions for the change via the Neutron team meeting slot for neutron-lib. Subsequently follow-up with an email to openstack-dev list using a subject with [neutron] neutron-lib impact providing additional details as necessary. Ideally we can identify the main impacted subprojects by grepping the OpenStack code.
  • Prepare a neutron core patch to remove and update the rehomed code from its source. This can be done without a debtcollector notice by following the steps here. In the patch’s commit message include the NeutronLibImpact so that we can easily query for such changes. Mark the patch as a work in progress with a -1 workflow vote.
  • If the change is significant enough, it may warrant a “reference implementation” in an impacted subproject to ensure the impacts are fully understood. Testing this change can be done using the Depends-On: approach described in the review guidelines.
  • If you are a core reviewer and about to approve a NeutronLibImpact change, please consider checking the state of all Stadium subprojects by looking at the grafana periodic dashboard. This dashboard shows the status of subprojects’ unit tests against neutron and neutron-lib master branches, and even though it is not exactly validating unit tests against a released version of neutron-lib it may be enough of an alarm bell to indicate that something might be wrong because of a patch that recently landed in neutron (assuming that the subprojects still has direct neutron imports). The check happens daily therefore consider waiting to approve if you are either aware of another impactful change recently merged that has not been yet processed or you see failure rates spiking.


  • 348472 removes a validator in neutron that was rehomed to neutron-lib.