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Oslo/VersioningPolicy

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Oslo Versioning Policy

As part of the push to release code from the oslo incubator in stand-alone libraries, we have had several different discussions about versioning and release schedules. This is an attempt to collect all of the decisions we have made in those discussions and to lay out the rationale for the approach we are taking.

Background

We have two types of oslo libraries. Libraries like oslo.config and oslo.messaging were created by extracting incubated code, updating the public API, and packaging it. Libraries like cliff and taskflow were created as standalone packages from the beginning, and later adopted by the oslo team to manage their development and maintenance.

Incubated libraries have been released at the end of a release cycle, as with the rest of the integrated packages. Adopted libraries have historically been released "as needed" during their development. We would like to synchronize these so that all oslo libraries are officially released with the rest of the software created by OpenStack developers.

The first release of oslo.config was 1.1.0, as part of the grizzly release. The first release of oslo.messaging was 1.2.0, as part of the havana release. oslo.config was also updated to 1.2.0 during havana. All current adopted libraries have release numbers less than 1.0.0.

In the past, alpha releases of oslo libraries have been distributed as tarballs on an openstack server, with official releases going to PyPI. Applications that required the alpha release specified the tarball in their requirements list, followed by a version specifier. This allowed us to prepare alpha releases, without worrying that their release would break continuous-deployment systems by making new library releases available to pip. This approach still made it difficult for an application developer to rely on new features of an oslo library, until an alpha version was produced.

When the PyPI mirror was introduced in our CI system, relying on tarballs not available on the mirror conflicted with our desire to have the gate system install *only* from the package mirror. As we are now installing only from the mirror, we need to publish our alpha releases in a format that will work with the mirror.

We already gate OpenStack applications and oslo libraries using integration tests using the normal devstack-gate jobs. During Icehouse we had a couple of oslo library releases that broke unit tests of applications after the library was released. We plan to address that with separate gating jobs during juno. In addition to that gating, we need to support developers who want to use new features of oslo libraries before official releases are available.

Synchronizing with the rest of OpenStack

The Oslo team could release libraries at any point, without concern for the release schedule of the rest of OpenStack. We have to be prepared for libraries we do not maintain to be updated at any point, so this wouldn't be adding a new aspect to our release and testing processes. However, Oslo is part of OpenStack and so we want to be on the same schedule.

Mark has written a good justificiation for this, which is summarized as "my instinct is to do everything just like any of the other core projects except in those cases where Oslo really is a special case." With Oslo following the release schedule of the other projects, we get all of the benefits (shifting focus from features to bugs; stable branches; synchronization with the users of our libraries; the OpenStack release manager).

A Version Numbering Scheme

At the Juno summit, Josh proposed that we use semantic versioning (SemVer) for oslo libraries. Part of that proposal also included ideas for allowing breaking backwards compatibility at some release boundaries, and this policy does not yet address that issue. The first step is choosing a rational release versioning scheme.

SemVer is widely used and gives us relatively clear guidelines about choosing new version numbers. It supports alpha releases, which are going to be key to meeting some of our other requirements. Oslo started using pbr's modified SemVer for new releases, beginning in the Juno cycle.

Juno Updates

The versions for existing libraries oslo.config and oslo.messaging will be incremented from their Icehouse versions but updating the minor number (1.x.0) at the end of the Juno cycle.

All adopted libraries using numbers less than 1.0 will be released as 1.0.0 at the end of the Juno cycle, based on the fact that we expect deployers to use them in production.

Releases during Juno should *all* be marked as alphas of the anticipated upcoming SemVer-based release number (1.0.0.0aN or 1.2.0.0aN or whatever). The new CI system can create packages as Python wheels and publish them to the appropriate servers, which means projects will no longer need to refer explicitly to pre-release tarballs. pip won't install alpha libraries unless you explicitly request them with a command line flag to install any alphas available or you explicitly require the alpha version. pip <= 1.3 didn't support the flag for controlling alphas (they were always seen and installed), but also didn't support wheels, so we publish alphas only as wheels to ensure that older pips don't see them.

After Juno

Development versions will be tagged as alphas during the release cycle, based on the appropriate estimated SemVer update to be made at the end of the release cycle.

Final releases will be cut during the RC period at the end of the cycle, as with the other projects.

Frequent Alpha Releases

While we can run gate jobs using the master branch of oslo libraries, developers will have to take extra steps to run unit tests this way locally. To reduce this process overhead, while still ensuring that developers use current versions of the code, we produce alpha releases of libraries during the release cycle fairly frequently. We have a weekly check-up during the oslo team meetings on Fridays, and tag releases early on Mondays when deemed necessary. Waiting until Monday prevents us from introducing a gate issue just before the weekend starts.

Patch Releases

Updates to existing library releases can be made from stable branches. Checking out stable/icehouse of oslo.config for example would allow a release 1.3.1. We don't have a formal policy about whether we will create patch releases, or whether applications are better off using the latest release of the library. Do we need one?

We do not typically use upper bounds on the requirements specifications for oslo libraries, so new releases may automatically be adopted by continuous-deployment systems building packages for stable branches of OpenStack applications. Although we have been careful about API compatibility in the past, there is a chance that a new release could break an older application. Applications could add an upper bound using SemVer numbering if they choose, although that may prevent them from seeing bug fixes so it is not recommended.

Unit test gate jobs

We have a blueprint for Juno to add cross-project unit test gating for applications and oslo libraries. This will allow us to verify that tests for applications do not break when oslo libraries change, but also that those tests do not make assumptions about oslo library implementation details.

Depending on how the job is implemented, we may be able to reuse the tools to let developers run the same tests locally. More thought is needed here; stay tuned.

Tagging milestones in libraries

We don't tag libraries at the milestones like we do with applications, since the tags we use for milestones (e.g., 2014.2.b1) aren't valid versions for libraries and would be out of order with other releases anyway. We may tag an alpha release around the time of the milestone, but since we do those on demand anyway there's no strict rule that we must do it at that time.

References