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

Salvatore Orlando sorlando at nicira.com
Fri Aug 8 22:28:22 UTC 2014

"If we want to keep everything the way it is, we have to change everything"

This is pretty much how I felt after reading this proposal, and I felt that
this quote, which Ivar will probably appreciate, was apt to the situation.
Recent events have spurred a discussion about the need for a change in
process. It is not uncommon indeed to believe that by fixing the process,
things will inevitably change for better. While no-one argues that flaws in
processes need to be fixed, no process change will ever change anything, in
my opinion, unless it is aimed at spurring change in people as well.

>From what I understand, this proposal starts with the assumption that any
new feature which is committed to Neutron (ie: has a blueprint approved),
and is not a required neutron component should be considered as a preview.
This is not different from the process, which, albeit more informally, has
been adopted so far. Load Balancing, Firewall, VPN, have all been
explicitly documented as experimental in their first release; I would argue
that even if not experimental anymore, they may not be considered stable
until their stability was proven by upstream QA with API and scenario tests
- but this is not sanctioned anywhere currently, I think.

According to this proposal, for preview features:
- all the code would be moved to a "preview" package
- Options will be marked as "preview"
- URIs should be prefixed with "preview"
- CLIs will note the features are "preview" in their help strings
- Documentation will explicitly state this feature is "preview" (I think we
already mark them as experimental, frankly I don't think there are a lot of
differences in terminology here)
- Database migrations will be in the main alembic path as usual
- CLI, Devstack and Heat support will be available
- Can be used by non-preview neutron code
- Will undergo the usual review process
- QA will be desirable, but will done either with "WIP" tempest patches or
merging the relevant scenario tests in the preview feature iself
- The feature might be promoted or removed, but the process for this is not
yet defined.

I don't think this change in process will actually encourage better
behaviour both by contributors and core reviewers.
I reckon that better behaviour might be encouraged by forcing developer and
reviewers to merge in the neutron source code tree only code which meets
the highest quality standards. A change in process should enforce this -
and when I think about the criteria, I think at the same kind of criteria
we're being imposed to declare parity with nova. Proven reliability, and
scalability should be a must. Proven usability should be a requirement for
all new APIs.
On the other hand we also need to avoid to over bureaucratise Neutron -
nobody loves that - and therefore ensure this process is enforced only when
really needed.

Looking at this proposal I see a few thing I'm not comfortable with:
- having no clear criterion for exclusion a feature might imply that will
be silently bit-rotting code in the preview package. Which what would
happen for instance if we end up with a badly maintained feature , but
since one or two core devs care about it, they'll keep vetoing the removal
- using the normal review process will still not solve the problem of slow
review cycles, pointless downvotes for reviewers which actually just do not
understand the subject matter, and other pains associated with lack of
interest from small or large parts of the core team. For instance, I think
there is a line of pretty annoyed contributors as we did not even bother
reviewing their specs.
- The current provision about QA seems to state that it's ok to keep code
in the main repo that does not adhere to appropriate quality standards.
Which is the mistake we did with lbaas and other features, and I would like
to avoid. And to me it is not sufficient that the code is buried in the
'preview' package.
- Mostly important, this process provides a justification for contributors
to push features which do not meet the same standards as other neutron
parts and expect them to be merged and eventually promoted, and on the
other hand provides the core team with the entitlement for merging them -
therefore my main concern that it does not encourages better behaviour in
people, which should be the ultimate aim of a process change.

If you managed to read through all of this, and tolerated my dorky
literature references, I really appreciate your patience, and would like to
conclude that here we're discussing proposals for a process change, whereas
I expect to discuss in the next neutron meeting the following:
- whether is acceptable to change the process now
- what did go wrong in our spec review process, as we ended up with at
least an approved spec which is actually fiercely opposed by other core
team members.

Have a good weekend,

[1] Quote from "Il Gattopardo" by Giuseppe Tomasi di Lampedusa (english
name: The Leopard)

On 8 August 2014 22:21, 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.]
> 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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> OpenStack-dev at lists.openstack.org
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