Stable Branches

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.
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.
Unmaintained 6 months The branch is under Extended Maintenance rules, but there are no maintainers
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 Extended Maintenance or even End of Life.

Note

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.

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.

Per Project Stable teams and the Stable Maintainers are responsible for all tagged projects during the this phase.

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.

The HEAD of the appropriate branch will be tagged as $series-em, for example: https://review.openstack.org/608296/

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.

Note

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

Unmaintained

At this stage of the project/branch the Extended Maintenance policy applies but CI may not be working and/or there aren’t any active maintainers. Projects that remain in this state for 6 months will be transitioned to End of Life. Should maintainers be found a project can be placed back into Extended Maintenance.

End of Life

After a project/branch exceeds the time allocation as Unmaintained, it will be become End of Life. The HEAD of the appropriate branch will be tagged as $series-eol and the branch deleted.

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. Originally that group should be the project Stable Branch Cross-Project Liaison + the stable maintenance core team. Those groups are managed by the stable maintenance core team, names are added after the suggestion of the Stable Branch cross-project liaison.

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-dev mailing list and expect a reasonably prompt response.

    Note

    Projects with the stable:follows-policy tag should be running the periodic-<release> jobs as defined in the openstack-infra/project-config repo. Here is an example of running periodic-kilo and periodic-liberty jobs on Designate.

  6. Stable branch cross-project liaisons should be available in the #openstack-stable channel on freenode 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-dev 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.

Note

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

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! 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.

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.

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.

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