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:

State	Time frame	Summary
Maintained	Approximately 18 months	All bugfixes (that meet the criteria described below) are appropriate. Releases produced.
Unmaintained	While there is community interest.	Only SLURP releases. All bugfixes (that meet the criteria described below) are appropriate. No Releases produced, reduced CI commitment.
End of Life (EOL)	N/A	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 Unmaintained or even End of Life.

Note

How can I tell what state a branch is in?

Current development branch

This is the master branch in a repository.

The project’s core team (for example, cinder-core) is responsible for merging changes into this branch.

Maintained branches

These are the stable/$series branches in a repository, for example, stable/2023.1.

The project’s stable core team (for example, cinder-stable-maint), which may be a subset of the core team, is responsible for merging changes into Maintained branches.

A project’s PTL or release team liaison must acknowledge proposed releases from a Maintained branch, which are then subject to approval by the OpenStack Release Management Team.

See Stable maintenance teams for details.

Unmaintained branches

These are the unmaintained/$series branches in a repository, for example, unmaintained/xena.

There is a global openstack-unmaintained-core team that is responsible for merging changes into Unmaintained branches. Optionally, an individual project may have a $project-unmaintained-core team (for example, ironic-unmaintained-core) that has this responsibility, and which may override the global team’s approval power on Unmaintained branches.

Releases are not allowed from Unmaintained branches.

Changes to Unmaintained branches are expected to be Appropriate Fixes as described elsewhere in this document.

End of Life

These do not exist as branches in the code repository, but can be recreated by checking out a $series-eol tag, for example, train-eol.

Maintained

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.

Unmaintained

Note

Only SLURP branches are eligible for Unmaintained status.

After a branch is no longer in Maintained status, the branch is tagged $series-eom, the stable/$series branch is deleted, and an unmaintained/$series branch is created based on the $series-eom tag.

Releases are not allowed from Unmaintained branches.

By default, only the latest eligible Unmaintained branch is kept open. To prevent an Unmaintained branch from automatically transitioning to End of Life once a newer eligible branch enters the status, the Unmaintained branch liaison must manually opt-in as described below for each branch.

Note

An Unmaintained liaison may be appointed by the PTL, but there should not be an expectation on the upstream community team to keep the branch open. Members of the community interested in a given branch are encouraged to engage with the appropriate project team early in its life-cycle to ensure this process runs well. In the absence of identified maintainers the branch will automatically transition to End of Life.

To opt-in to keep the Unmaintained branch open, the PTL or Unmaintained liaison must -1 the appropriate patch in the openstack/releases repo to EOL the branch. Please contact the PTL or Unmaintained liaison to show interest in helping keep the branch open with backports and reviews. The patch to EOL the Unmaintained branch will be merged no earlier than one month after its proposal. Even if a PTL or liaison has voted +1 to EOL the branch, the patch must remain open for the full grace period to permit other community members the opportunity to volunteer to take it over.

To be eligible to opt-in, a branch must have functional CI including unit tests for the published supported python versions for that OpenStack release. Functional CI means all configured tests pass and do not generate errors in Zuul.

Additionally, no SLURP branches may be skipped between the oldest unmaintained branch and the current maintained releases. This makes sure operators have an upgrade path from one SLURP to the next all the way to maintained releases.

Note

For further details about Unmaintained status, please take a look at the OpenStack Technical Committee’s resolution Unmaintained status replaces Extended Maintenance as amended to define the openstack-unmaintained-core Gerrit Group.

Warning

Tempest and its plugins are branchless and there is no guarantee that Unmaintained branches will continue to be supported by the master version of tempest or its plugins.

Note

For more information, see the Tempest Stable Branch Support Policy.

If Tempest master starts breaking when testing Unmaintained branches, then we need to use the last compatible version of Tempest and its plugins.

To make the last compatible version of Tempest and its plugins available for a particular branch, at the time the branch enters Unmaintained status the Tempest maintainers will release a new tag at a master hash with the name $series-last (as well as a new version number). The maintainers of tempest plugins will also release $series-last tags for each of the plugins.

This makes it easy for Tempest consumers who want to continue CI testing of an Unmaintained branch (either upstream or in a production cloud) to identify the last compatible versions of Tempest and its plugins for that branch. It is also more reliable than requiring anyone who wishes to use Tempest on an Unmaintained branch to manually try and find the working version.

For an example of creating $series-last tags for Tempest and its plugins, take a look at these Gerrit reviews: https://review.opendev.org/q/topic:%22tempest-plugin-stein-last%22+(status:open%20OR%20status:merged)

End of Life

After a branch is ineligible to remain active as 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: https://review.opendev.org/#/c/677478/)

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.

Note

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.

Note

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.

Warning

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.

   Note

   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.

Unmaintained branch maintenance

Unmaintained branches are not the responsibility of individual project teams (though, of course, there is no prohibition against individual project team members working on Unmaintained branches).

Instead, there is a global openstack-unmaintained-core team that has access rights to maintain the CI running on Unmaintained branches, and to merge appropriate changes into Unmaintained branches.

Additionally, each project may have (but is not required to have) a Gerrit team called PROJECTNAME-unmaintained-core to handle all work on that project’s Unmaintained branches. This group is managed by the PTL or the Unmaintained branch liaison if there is one. The group is created by proposing an appropriate set of permissions to the project’s Gerrit ACLs in the openstack/project-config repository. See https://review.opendev.org/c/openstack/project-config/+/902796 for an example.

Note

To become a member of the openstack-unmaintained-core team, first the stable policy has to be understood, as it still applies to unmaintained branches as well. Then contact the group itself and signal the interest of becoming a member of the group and the intention to maintain a project (or multiple projects) and its CI, then the team will decide and grant membership.

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.

Processes

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.

Note

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.

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

Note

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.

Conflicts

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: https://review.opendev.org/686292/

Note

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

Change-Ids

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.

Warning

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.

Releases

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

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

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

13. 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

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

15. Zaqar (Message service): zaqar