Branch and release maintenance for the Kata Containers project.
As detailed in the release documentation, the Kata Containers project makes use of semantic versioning. A release version is described by MAJOR.MINOR.PATCH. Early in the project, we will introduce many new features, which require minor version changes as well as bug fixes. To facilitate a stable user environment, Kata will begin to provide stable branch-based releases and a master branch release.
No new features should be introduced to stable branches. This is intended to limit risk to users, providing only bug and security fixes.
Kata Containers will maintain two stable release branches in addition to the master branch.
Once a new MAJOR or MINOR release is created from master, a new stable branch is created for
the prior MAJOR or MINOR release and the older stable branch is no longer maintained. End of
maintainence for a branch is announced on the Kata Containers mailing list. Users can determine
the version currently installed by running kata-runtime kata-env. It is recommended to use the
latest stable branch available.
A couple of examples follow to help clarify this process.
A bug fix is submitted against the runtime which does not introduce new inter-component dependencies. This fix is applied to both the master and stable branches, and there is no need to create a new stable branch.
| Branch | Original version | New version |
|---|---|---|
master |
1.3.0-rc0 |
1.3.0-rc1 |
stable-1.2 |
1.2.0 |
1.2.1 |
stable-1.1 |
1.1.2 |
1.1.3 |
A new feature is introduced, which adds a new inter-component dependency. In this case a new stable branch is created (stable-1.3) starting from master and the older stable branch (stable-1.1) is dropped from maintenance.
| Branch | Original version | New version |
|---|---|---|
master |
1.3.0-rc1 |
1.3.0 |
stable-1.3 |
N/A | 1.3.0 |
stable-1.2 |
1.2.1 |
1.2.2 |
stable-1.1 |
1.1.3 |
(unmaintained) |
Note, the stable-1.1 branch will still exist with tag 1.1.3, but under current plans it is not maintained further. The next tag applied to master will be 1.4.0-rc0.
Development that occurs against the master branch and applicable code commits should also be submitted against the stable branches. Some guidelines for this process follow::
- Only bug and security fixes which do not introduce inter-component dependencies are candidates for stable branches. These PRs should be marked with "bug" in GitHub.
- Once a PR is created against master which meets requirement of (1), a comparable one should also be submitted against the stable branches. It is the responsibility of the submitter to apply their pull request against stable, and it is the responsibility of the reviewers to help identify stable-candidate pull requests.
The test repository is forked to create stable branches from master. Full CI runs on each stable and master PR using its respective tests repository branch.
Ideally, the continuous integration infrastructure will run the same test suite on both master and the stable branches. When tests are modified or new feature tests are introduced, explicit logic should exist within the testing CI to make sure only applicable tests are executed against stable and master. While this is not in place currently, it should be considered in the long term.
Releases are made on a weekly cadence for patch releases, which include a GitHub release as
well as binary packages. These patch releases are made for both stable branches, and a 'release candidate'
for the next MAJOR or MINOR is created from master. If there are no changes across all the repositories, no
release is created and an announcement is made on the developer mailing list to highlight this.
If a release is being made, each repository is tagged for this release, regardless
of whether changes are introduced.
Minor releases are less frequent in order to provide a more stable baseline for users. They are currently running on a six week cadence. As the Kata Containers code base matures it is expected this will become a much longer duration.
Kata guarantees compatibility between components that are within one minor release of each other.
This is critical for dependencies which cross between host (runtime, shim, proxy) and the guest (hypervisor, rootfs and agent). For example, consider a cluster with a long-running deployment, workload-never-dies, all on kata version 1.1.3 components. If the operator updates the Kata components to the next new minor release (i.e. 1.2.0), we need to guarantee that the 1.2.0 runtime still communicates with 1.1.3 agent within workload-never-dies.
Handling live-update is out of the scope of this document. See this kata-runtime issue for details.