Stable Branches

The stable branches are intended to be a safe source of fixes for high impact bugs and security issues which have been fixed on master since a given release.

Stable branches are cut from the last release of a given deliverable, at the end of the common 6-month development cycle.

Maintenance phases

Project stable branches will be in one of the following states:


Time frame



Approximately 18 months

All bugfixes (that meet the criteria described below) are appropriate. Releases produced.

Extended Maintenance

While there are community members maintaining it.

All bugfixes (that meet the criteria described below) are appropriate. No Releases produced, reduced CI commitment.

End of Life (EOL)


Branch no longer accepting changes.

It is not required that all projects for a given branch transition between phases at the same time. For example it’s quite reasonable for the stable/$series branch of openstack/long-life-project to still be in the Maintained phase while all other projects have transitioned to either Extended Maintenance or even End of Life.


At this time the exact mechanism for describing and updating this state is undefined but it’s probable it will involved updating a meta-data in a projects deliverable file in the openstack/releases repo.


For any project/branch combination that is considered Maintained, OpenStack Infrastructure, OpenStack Vulnerability Management and QE tools are expected to work and be active. Project teams will produce consumable releases and upgrades are tested.

During this phase, per Project Stable teams and the Stable Maintainers are responsible for all projects which asserted they follow the stable branch policy.

Extended Maintenance

Once a branch reaches Extended Maintenance project teams will cease producing releases and OpenStack Vulnerability Management will be reasonable efforts only. There is no statement about the level of testing and upgrades from Extended Maintenance are not supported within the Community. There should not be an expectation on the upstream community team to keep maintaining the Extended Maintenance stable branches upstream testing. We will keep them open as long as possible so that any operator or user will be able to backport required fixes. Without regular comprehensive maintenance, it is quite possible that someone proposing a backport to an EM branch will find that tests have broken since the last successful merge. This means that tests (or test configuration) might need to be fixed, reduced, or reconfigured before the backport itself can be evaluated and merged. The onus for that falls on the backporter or the group of people looking after a specific release.

The last release of the appropriate branch will be tagged as $series-em, for example: For all projects that follow the stable policy a patch with a $series-em tag will be automatically generated after the final release from the latest development cycle happened. This is because this is a less busy period in development perspective compared to feature freeze and release periods.

Tempest and its plugins are branchless and does not guarantee about supporting the Extended Maintenance branches with their master version. For more detail on the Tempest policy for stable branch testing refer to this doc. If Tempest master start breaking on Extended Maintenance branches testing then we need to use the last compatible version of Tempest and its plugins. To know the last compatible version of Tempest and its plugins, we need to release the new tag with master hash (at the time of branch reaches Extended Maintenance) with name $series-last as well as the new version number. This will help to easily detect the last compatible versions of Tempest and its plugins (instead of manually try and find the working version) for testing it at upstream as well at production cloud. Example:

Members of the community interested in a given project/branch are encouraged to engage with the appropriate stable team early in its life-cycle to ensure this process runs well. In the absence of identified maintainers the project will immediately enter the 6 month notification period as described under End of Life below.


Some project teams may choose to NOT enter extended maintenance and go directly to End of Life. At this point should a group wish to maintain that branch of a project they can do so within license and trademark constraints. Some OpenStack CI testing may be available via Zuul drivers


For further details about the Extended Maintenance please take a look at the OpenStack governance’s related resolution.

End of Life

After a project/branch becomes unmaintained or a team decides to explicitly end support for a branch, it will become End of Life. The HEAD of the appropriate branch will be tagged as $series-eol and the branch deleted.

To initiate this transition, either the PTL of the given project or other stable maintainer should:

  1. Send an announcement to the openstack-discuss mailing list (in order to give some time for others to step up as maintainers if there are volunteers).

  2. Remove any related zuul jobs that are defined in other repositories and not needed anymore.

  3. Propose a patch against the given project/repository. (For example, see:

  4. After the branch is tagged with $series-eol, request the Release Management team to delete the branch.

Appropriate Fixes

Only a limited class of changes are appropriate for inclusion on the stable branch. A number of factors must be weighed when considering a change:

  1. The risk of regression: even the tiniest changes carry some risk of breaking something and we really want to avoid regressions on the stable branch

  2. The user visible benefit: are we fixing something that users might actually notice and, if so, how important is it?

  3. How self-contained the fix is: if it fixes a significant issue but also refactors a lot of code, it’s probably worth thinking about what a less risky fix might look like

  4. Whether the fix is already on master and all consequent stable branches: a change must be a backport of a change already merged onto master, unless the change simply does not make sense on master. Same applies to N-2 releases, where N is master, in which case both N-1 and N branches should have the patch merged and so on.


It’s nevertheless allowed to backport fixes for other bugs if their safety can be easily proved. For example, documentation fixes, debug log message typo corrections, test only changes, patches that enhance test coverage, configuration file content fixes can apply to all supported branches. For those types of backports, stable maintainers will decide on case by case basis.


Some patches may get exception from rule 4 above. These are patches that do not touch production code, like test-only patches, or tox.ini changes that fix major gate breakage, etc.; or security patches that should not take much time to merge once the patches are published. In those cases, stable patches may be pushed into gate without waiting for all consequent branches to be fixed.


In case review process reveals issues in the master patch which require rework after stable patches are merged, it’s expected that additional changes are merged into stable branches to avoid unneeded difference between branches. So use the exception with due care.

Anyone can propose stable branch backports. See Proposing Fixes for more information on how to do that.

Stable maintenance teams

Each project team should designate a stable branch cross-project liaison as the main point of contact for all stable branch support issues in the team. If nobody is specifically designated, the PTL will be assumed to cover that duty.

Project-specific teams

Each project with a stable branch will have a project-specific stable maintenance Gerrit team called PROJECTNAME-stable-maint. This team will have CodeReview+2 and Workflow+1 rights over the stable branches, and be in charge of reviewing backports for a given project, following the rules of the stable branch policy. That group should be the project Stable Branch core (not necessary to be master core) + the stable maintenance core team. That group is managed by the project team like they manage their master branch core team. To manage that group or stable policies, they can consult with the stable maintenance core team.

Stable Maintenance Core team

The stable maintenance core team is responsible for the definition and enforcement of the Stable Branch policy. It will be granting exceptions for all questionable backports raised by project-specific stable maintenance groups, providing backports reviews help everywhere, maintaining the stable branch policy (and make sure its rules are respected), educating proposed project-specific team members on those rules and adding them to those project-specific teams.

Active Maintenance

Project-specific teams are expected to be actively maintaining their stable branches which generally includes:

  1. Following the Review guidelines. Specifically, not allowing backports of new features, new dependencies, or backward incompatible changes.

    • Hint: if a project version has a cap in stable branch global-requirements in stable/liberty or later, it means there was a backward incompatible change which broke that stable branch. This generally applies to libraries and client projects.

  2. Proactively identifying and backporting significant bug fixes from master to stable branches. This means the team is trying to get high impact bugs fixed on stable before anyone hits them and has to report a bug or propose a backport after the fact (after they already hit the issue in their production cloud). There is no rule about how often or how many bugs found and fixed in master should be backported to stable branches. The main idea is to get regressions and other high-impact issues resolved on all appropriate branches quickly.

  3. Monitoring the backlog of open backport reviews and actually reviewing them in a timely manner.

  4. Releasing frequently enough to get fixes out without overwhelming the release team or consumers. In general, security fixes and other critical bug fixes should be released quickly. Otherwise when there are a reasonable amount of unreleased fixes committed, teams should be looking at doing a release. Milestone boundaries during the master release schedule are also good times to be inspecting the list of unreleased changes to see if a stable point release should happen.

  5. Monitoring and resolving issues in the continuous integration ‘gate’ system. This basically means making sure there aren’t things blocking proposed backports from passing tests. These could be project-specific or global in nature and are usually tracked in the stable tracker etherpad. From time to time the Stable Maintenance Core team may also ask for help from individual projects in IRC or the openstack-discuss mailing list and expect a reasonably prompt response.


    Projects which asserted they follow the stable branch policy should be running the periodic-stable-jobs template in their project’s Zuul configuration file, usually .zuul.yaml (example .zuul.yaml) or zuul.d/project.yaml (example zuul.d/project.yaml).

    The template is defined in zuul.d/project-templates.yaml in the openstack/openstack-zuul-jobs repo and is maintained by the OpenStack QA team.

  6. Stable branch cross-project liaisons should be available in the #openstack-stable channel on OFTC IRC to answer questions or be made aware of issues.

Review guidelines

Each project stable review team need to balance the risk of any given patch with the value that it will provide to users of the stable branch. A large, risky patch for a major data corruption issue might make sense. As might a trivial fix for a fairly obscure error handling case.

Some types of changes are completely forbidden:

  • New features

  • Changes to the external HTTP APIs

  • Changes to Nova’s internal AMQP API

  • Changes to the notification definitions

  • DB schema changes

  • Incompatible config file changes

Proposed backports breaking any of the above guidelines can be discussed as exception requests on the openstack-discuss list (prefix with [stable]) where the stable maintenance core team will have the final say.

Each backported commit proposed to Gerrit should be reviewed and +2ed by two project-specific stable maintenance team members before it is approved. Where a team member has backported a fix, a single other +2 is sufficient for approval.

If unsure about the technical details of a given fix, project-specific stable maintenance team members should consult with the appropriate project core reviewers for a more detailed technical review.

If unsure if a fix is appropriate for the stable branch, project-specific stable maintenance team members should seek stable maintenance core team members opinion.

Existing core reviewers are greatly encouraged to join the stable maintenance teams in order to help with reviewing backports, judging their appropriateness for the stable branch and approving them.

Fixes for embargoed security issues receive special treatment. See the chapter on vulnerability management for more information.


OpenStack development typically has 3 branches active at any point of time, master (the current development release), stable (the most recent release) and oldstable (previous release). There can from time to time exist older branches but a discussion around that is beyond the scope of this guide.

In order to accept a change into $release it must first be accepted into all releases back to master.

For the sake of discussion assume a hypothetical development milestones:

  • The development branch (master) will be the Uniform release.

  • The N-1 branch is stable/tango

  • The N-2 branch is stable/sierra

  • The N-3 branch is stable/romeo

  • and so on

Backport examples:

  • A change for Tango must exist in master

  • A change for Sierra must exist in stable/tango and master

  • A change for Romeo must exist in stable/sierra, stable/tango and master

  • and so on

Proposing Fixes

Anyone can propose a cherry-pick to the stable-maint team.

One way is that if a bug in launchpad looks like a good candidate for backporting - e.g. if it’s a significant bug with the previous release - then just nominating the bug for a stable series (either stable or oldstable) will bring it to the attention of the maintainers e.g. Nova Kilo nominations

If you don’t have the appropriate permissions to nominate the bug, then tagging it with e.g. $release-backport-potential is also sufficient e.g. Nova Liberty potential

The best way to get the patch merged in a timely manner is to send it backported by yourself. To do so, you may try to use the “Cherry Pick To” button in the Gerrit UI for the original patch in master. Gerrit will take care of creating a new review, modifying the commit message to include ‘cherry-picked from …’ line etc.


The backport must match the master commit, unless there is a serious need to differ e.g gate failure, test framework changed in master, code refactoring or some other reason. If you get a suggestion to enhance your backport in some way that would be contrary to this intent, the reviewer should be referred to the warning above.


For code that touches code from oslo-incubator, special backporting rules apply. More details in Oslo policies

You can use git-review to propose a change to the hypothetical stable branch with:

$ git checkout -t origin/stable/tango
$ git cherry-pick -x $master_commit_id
$ git review stable/tango


cherry-pick -x option includes ‘cherry-picked from …’ line in the commit message which is required to avoid Gerrit bug

Failing all that, just ping one of the team and mention that you think the bug/commit is a good candidate.


If the patch you’re proposing will not cherry-pick cleanly, you can help by resolving the conflicts yourself and proposing the resulting patch. Please keep “Conflicts” lines in the commit message to help reviewers, for example:


If a cherry-picked patch’s commit message contains “Conflicts” lines that are not valid anymore in the target branch, then remove those lines.


When cherry-picking a commit, keep the original Change-Id and gerrit will show a separate review for the stable branch while still allowing you to use the Change-Id to see all the reviews associated with it. See this change as an example.


Change-Id line must be in the last paragraph. Conflicts in the backport add a new paragraph, creating a new Change-Id but you can avoid that by moving conflicts above the paragraph with Change-Id line or removing empty lines to make a single paragraph.


For stable releases, branches should be released in the same order as of backporting fixes. For example, to release a branch N-1, we should first release the branch N and continue in the same sequence of releasing N, N-1, N-2 and so on.

It is not required to release all stable branches together but to avoid conflict, we should only release branch N-1 with changes already released with branch N release and should avoid having the case where an older branch release contain fixes that does not exist in a recent branch release. There can be exceptions to this case but it is the preferred way of releasing stable branches.

Email Notifications

If you want to be notified of new stable patches you can create a watch on the gerrit watched projects screen with the following settings.

Project Name: All-Projects
     Only If: branch:stable/liberty

Then check the “Email Notifications - New Changes” checkbox. That will cause gerrit to send an email whenever a matching change is proposed, and better yet, the change shows up in your ‘watched changes’ list in gerrit.

See the docs for gerrit notify configuration and the gerrit search syntax.

Bug Tags

Bugs tagged with $release-backport-potential are bugs which apply to a stable release and may be suitable for backporting once fixed. Once the backport has been proposed, the tag should be removed.

Gerrit tags bugs with in-stable-$release when they are merged into the stable branch. The release manager later removes the tag when the bug is targeted to the appropriate series.

Gate Status

Keeping the stable branches in good health in an ongoing effort. To see what bugs are currently causing gate failures and preventing code from merging into stable branches, please see the stable tracker etherpad, where we will track current bugs and in-flight fixes.

Scheduled test runs occur daily for each project’s stable branch. If failures crop up, the bot will email the openstack-stable-maint mailing list. It is best to react quickly to these and get them resolved ASAP to prevent them from piling up. Please subscribe if you’re interested in helping out.

Project teams which asserted they follow the stable branch policy

This list can be updated if there is any change in their stable branch policy (project stop or start following the stable branch policy).

  1. Barbican (Key Manager service): barbican

  2. Cinder (Block Storage service): cinder, cinderlib, os-brick, python-brick-cinderclient-ext, python-cinderclient

  3. Designate (DNS service): designate, designate-dashboard, python-designateclient

  4. Glance (Image service): glance, glance-store, python-glanceclient

  5. Heat (Orchestration service): heat, python-heatclient

  6. Horizon (Dashboard): horizon

  7. Ironic (Bare Metal service): ironic, ironic-inspector, ironic-lib, ironic-python-agent, python-ironic-inspector-client, python-ironicclient

  8. Keystone (Identity service): keystone, keystoneauth, keystonemiddleware, pycadf, python-keystoneclient

  9. Manila (Shared File Systems service): manila

  10. Murano (Application Catalog service): murano, murano-agent, murano-dashboard, python-muranoclient

  11. Neutron (Networking service): neutron-fwaas, neutron, neutron-dynamic-routing, neutron-lib, neutron-vpnaas

  12. Nova (Compute service): nova, python-novaclient

  13. Octavia (Load-balancer service): octavia, octavia-dashboard, python-octaviaclient, octavia-lib

  14. Oslo (Common libraries): automaton, castellan, oslo.cache, oslo.config, oslo.context, oslo.db, oslo.messaging, oslo.middleware, oslo.policy, oslo.privsep, oslo.serialization, oslo.service, oslo.upgradecheck, oslo.utils, oslo.versionedobjects, oslo.vmware, stevedore

  15. Sahara (Data Processing service): python-saharaclient, sahara, sahara-dashboard, sahara-extra, sahara-image-elements, sahara-plugin-ambari, sahara-plugin-cdh, sahara-plugin-mapr, sahara-plugin-spark, sahara-plugin-storm, sahara-plugin-vanilla

  16. Swift (Object Storage service): python-swiftclient, swift

  17. Zaqar (Message service): zaqar