The need for releases
The beginning of a new release cycle is as good as any moment to question why we actually go through the hassle of producing OpenStack releases. Twice per year, on a precise date we announce 6 months in advance, we bless and publish source code tarballs of the various integrated projects in OpenStack. Every week we have a meeting that tracks our progress toward this common goal. Why ?
Releases vs. Continuous deployment
The question is particularly valid if you take into account the type of software that we produce. We don't really expect cloud infrastructure providers to religiously download our source code tarballs every 6 months and run from that. For the largest installations, running much closer to the master branch and continuously deploy the latest changes is a really sound strategy. We invested a lot of effort in our gating systems and QA automated testing to make sure the master branch is always runnable. We'll discuss at the OpenStack Summit next week how to improve CD support in OpenStack. We backport bugfixes to the stable branches post-release. So why do we continue to single out a few commits and publish them as "the release" ?
The need for cycles
The value is not really in releases. It is in release cycles.
Producing OpenStack involves the work of a large number of people. While most of those people are paid to participate in OpenStack development, as far as the OpenStack project goes, we don't manage them. We can't ask them to work on a specific area, or to respect a given deadline, or to spend that extra hour to finalize something. The main trick we use to align everyone and make us all part of the same community is to have a cycle. We have regular milestones that we ask contributors to target their features to. We have a feature freeze to encourage people to switch their mindset to bugfixing. We have weekly meetings to track progress, communicate where we are and motivate us to go that extra mile. The common rhythm is what makes us all play in the same team. The "release" itself is just the natural conclusion of that common effort.
A reference point in time
Singling out a point in time has a number of other benefits. It's easier to work on documentation if you group your features into a coherent set (we actually considered shortening our cycles in the past, and the main blocker was our capacity to produce good documentation often enough). It's easier to communicate about OpenStack progress and new features if you do it periodically rather than continuously. It's easier to have Design Summits every 6 months if you create a common brainstorm / implementation / integration cycle. The releases also serve as reference points for API deprecation rules, for stable release maintenance, for security backports.
If you're purely focused on the software consumption part, it's easy to underestimate the value of release cycles. They actually are one of the main reasons for the pace of development and success of OpenStack so far.
The path forward
We need release cycles... do we need release deliverables ? Do we actually need to bless and publish a set of source code tarballs ? My personal view on that is: if there is no additional cost in producing releases, why not continue to do them ? With the release tooling we have today, blessing and publishing a few tarballs is as simple as pushing a tag, running a script and sending an email. And I like how this formally concludes the development cycle to start the stable maintenance period.
But what about Continuous Deployment ? Well, the fact that we produce releases shouldn't at all affect our ability to continuously deploy OpenStack. The master branch should always be in good shape, and we definitely should have the necessary features in place to fully support CD. We can have both. So we should have both.