Hi everyone,
The (long) document below reflects the current position of the release management team on a popular question: should the OpenStack release cadence be changed? Please note that we only address the release management / stable branch management facet of the problem. There are other dimensions to take into account (governance, feature deprecation, supported distros...) to get a complete view of the debate.
Introduction ------------
The subject of how often OpenStack should be released has been regularly debated in the OpenStack community. OpenStack started with a 3-month release cycle, then switched to 6-month release cycle starting with Diablo. It is often thought of a release management decision, but it is actually a much larger topic: a release cadence is a trade-off between pressure to release more often and pressure to release less often, coming in from a lot of different stakeholders. In OpenStack, it is ultimately a Technical Committee decision. But that decision is informed by the position of a number of stakeholders. This document gives historical context and describes the current release management team position.
The current trade-off ---------------------
The main pressure to release more often is to make features available to users faster. Developers get a faster feedback loop, hardware vendors ensure software is compatible with their latest products, and users get exciting new features. "Release early, release often" is a best practice in our industry -- we should generally aim at releasing as often as possible.
But that is counterbalanced by pressure to release less often. From a development perspective, each release cycle comes with some process overhead. On the integrators side, a new release means packaging and validation work. On the users side, it means pressure to upgrade. To justify that cost, there needs to be enough user-visible benefit (like new features) in a given release.
For the last 10 years for OpenStack, that balance has been around six months. Six months let us accumulate enough new development that it was worth upgrading to / integrating the new version, while giving enough time to actually do the work. It also aligned well with Foundation events cadence, allowing to synchronize in-person developer meetings date with start of cycles.
What changed ------------
The major recent change affecting this trade-off is that the pace of new development in OpenStack slowed down. The rhythm of changes was divided by 3 between 2015 and 2021, reflecting that OpenStack is now a mature and stable solution, where accessing the latest features is no longer a major driver. That reduces some of the pressure for releasing more often. At the same time, we have more users every day, with larger and larger deployments, and keeping those clusters constantly up to date is an operational challenge. That increases the pressure to release less often. In essence, OpenStack is becoming much more like a LTS distribution than a web browser -- something users like moving slow.
Over the past years, project teams also increasingly decoupled individual components from the "coordinated release". More and more components opted for an independent or intermediary-released model, where they can put out releases in the middle of a cycle, making new features available to their users. This increasingly opens up the possibility of a longer "coordinated release" which would still allow development teams to follow "release early, release often" best practices. All that recent evolution means it is (again) time to reconsider if the 6-month cadence is what serves our community best, and in particular if a longer release cadence would not suit us better.
The release management team position on the debate --------------------------------------------------
While releasing less often would definitely reduce the load on the release management team, most of the team work being automated, we do not think it should be a major factor in motivating the decision. We should not adjust the cadence too often though, as there is a one-time cost in switching our processes. In terms of impact, we expect that a switch to a longer cycle will encourage more project teams to adopt a "with-intermediary" release model (rather than the traditional "with-rc" single release per cycle), which may lead to abandoning the latter, hence simplifying our processes. Longer cycles might also discourage people to commit to PTL or release liaison work. We'd probably need to manage expectations there, and encourage more frequent switches (or create alternate models).
If the decision is made to switch to a longer cycle, the release management team recommends to switch to one year directly. That would avoid changing it again anytime soon, and synchronizing on a calendar year is much simpler to follow and communicate. We also recommend announcing the change well in advance. We currently have an opportunity of making the switch when we reach the end of the release naming alphabet, which would also greatly simplify the communications around the change.
Finally, it is worth mentioning the impact on the stable branch work. Releasing less often would likely impact the number of stable branches that we keep on maintaining, so that we do not go too much in the past (and hit unmaintained distributions or long-gone dependencies). We currently maintain releases for 18 months before they switch to extended maintenance, which results in between 3 and 4 releases being maintained at the same time. We'd recommend switching to maintaining one-year releases for 24 months, which would result in between 2 and 3 releases being maintained at the same time. Such a change would lead to longer maintenance for our users while reducing backporting work for our developers.