[openstack-dev] [Neutron] Simple proposal for stabilizing new features in-tree

Sumit Naiksatam sumitnaiksatam at gmail.com
Fri Aug 8 21:15:38 UTC 2014

On Fri, Aug 8, 2014 at 1:21 PM, Robert Kukura <kukura at noironetworks.com> wrote:
> [Note - I understand there are ongoing discussion that may lead to a
> proposal for an out-of-tree incubation process for new Neutron features.
> This is a complementary proposal that describes how our existing development
> process can be used to stabilize new features in-tree over the time frame of
> a release cycle or two. We should fully consider both proposals, and where
> each might apply. I hope something like the approach I propose here will
> allow the implementations of Neutron BPs with non-trivial APIs that have
> been targeted for the Juno release to be included in that release, used by
> early adopters, and stabilized as quickly as possible for general
> consumption.]

+1. I think this proposal is simple to understand, has limited process
and operational overhead while achieving the desired benefit of
handing "preview" features to early adopters with the right set of

> According to our existing development process, once a blueprint and
> associated specification for a new Neutron feature have been reviewed,
> approved, and targeted to a release, development proceeds, resulting in a
> series of patches to be reviewed and merged to the Neutron source tree. This
> source tree is then the basis for milestone releases and the final release
> for the cycle.
> Ideally, this development process would conclude successfully, well in
> advance of the cycle's final release, and the resulting feature and its API
> would be considered fully "stable" in that release. Stable features are
> ready for widespread general deployment. Going forward, any further
> modifications to a stable API must be backwards-compatible with previously
> released versions. Upgrades must not lose any persistent state associated
> with stable features. Upgrade processes and their impact on a deployments
> (downtime, etc.) should be consistent for all stable features.
> In reality, we developers are not perfect, and minor (or more significant)
> changes may be identified as necessary or highly desirable once early
> adopters of the new feature have had a chance to use it. These changes may
> be difficult or impossible to do in a way that honors the guarantees
> associated with stable features.
> For new features that effect the "core" Neutron API and therefore impact all
> Neutron deployments, the stability requirement is strict. But for features
> that do not effect the core API, such as services whose deployment is
> optional, the stability requirement can be relaxed initially, allowing time
> for feedback from early adopters to be incorporated before declaring these
> APIs stable. The key in doing this is to manage the expectations of
> developers, packagers, operators, and end users regarding these new optional
> features while they stabilize.
> I therefore propose that we manage these expectations, while new optional
> features in the source tree stabilize, by clearly labeling these features
> with the term "preview" until they are declared stable, and sufficiently
> isolating them so that they are not confused with stable features. The
> proposed guidelines would apply during development as the patches
> implementing the feature are first merged, in the initial release containing
> the feature, and in any subsequent releases that are necessary to fully
> stabilize the feature.
> Here are my initial not-fully-baked ideas for how our current process can be
> adapted with a "preview feature" concept supporting in-tree stabilization of
> optional features:
> * Preview features are implementations of blueprints that have been
> reviewed, approved, and targeted for a Neutron release. The process is
> intended for features for which there is a commitment to add the feature to
> Neutron, not for experimentation where "failing fast" is an acceptable
> outcome.
> * Preview features must be optional to deploy, such as by configuring a
> service plugin or some set of drivers. Blueprint implementations whose
> deployment is not optional are not eligible to be treated as preview
> features.
> * Patches implementing a preview feature are merged to the the master branch
> of the Neutron source tree. This makes them immediately available to all
> direct consumers of the source tree, such as developers, trunk-chasing
> operators, packagers, and evaluators or end-users that use DevStack,
> maximizing the opportunity to get the feedback that is essential to quickly
> stabilize the feature.
> * The process for reviewing, approving and merging patches implementing
> preview features is exactly the same as for all other Neutron patches. The
> patches must meet HACKING standards, be production-quality code, have
> adequate test coverage, have DB migration scripts, etc., and require two +2s
> and a +A from Neutron core developers to merge.
> * DB migrations for preview features are treated similarly to other DB
> migrations, forming a single ordered list that results in the current
> overall DB schema, including the schema for the preview feature. But DB
> migrations for a preview feature are not yet required to preserve existing
> persistent state in a deployment, as would be required for a stable feature.
> * All code that is part of a preview feature is located under
> neutron/preview/<feature>/. Associated unit tests are located under
> neutron/tests/unit/preview/<feature>/, and similarly for other test
> categories. This makes the feature's status clear to developers and other
> direct consumers of the source tree, and also allows packagers to easily
> partition all preview features or individual preview features into separate
> optionally installable packages.
> * The tree structures underneath these locations should make it
> straightforward to move the preview feature code to its proper tree location
> once it is considered stable.
> * Tempest API and scenario tests for preview features are highly desirable.
> We need to agree on how to accomplish this without preventing necessary API
> changes. Posting WIP patches to the Tempest project may be sufficient
> initially. Putting Tempest-like tests in the Neutron tree until preview
> features stabilize, then moving them to Tempest when stabilization is
> complete, might be a better long term solution.
> * No non-preview Neutron code should import code from anywhere under the
> neutron.preview module, unless necessary for special cases like DB
> migrations.
> * URIs for the resources provided by preview features should contain the
> string "preview".
> * Configuration file content related to preview features should be clearly
> labeled as "preview".
> * Preview features should be documented similarly to any stable Neutron
> feature, but documents or sections of documents related to preview features
> should have an easily recognizable label that clearly identifies the feature
> as a "preview".
> * Support for preview features in client libraries, and in other projects
> such as Horizon, Heat, and DevStack, are essential to get the feedback
> needed from early adopters during feature stabilization. They are
> implemented normally, but should be labeled "preview" appropriately, such as
> in GUIs, in CLI help strings and in documentation so that end user
> expectations regarding stability are managed.
> * A process is needed to prevent long-term stagnation of features in the
> preview sub-tree. It is reasonable to expect a new feature to remain for one
> or two cycles, possibly with little change (other than bug fixes), before
> stabilizing. A suggested rule is that a new approved BP is required after
> two cycles, or the feature gets removed from the Neutron source tree (maybe
> moved (back) to an incubation repository).
> I would appreciate feedback via this email thread on whether this "preview
> feature" concept is worth further consideration, refinement and potential
> usage for approved feature blueprints, especially during the Juno cycle.
> I've also posted the proposal text at
> https://etherpad.openstack.org/p/neutron-preview-features for those
> interested in helping refine the proposal.
> Thanks,
> -Bob
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