OpenStack Nova Specifications
This git repository is used to hold approved design specifications for additions to the Nova project. Reviews of the specs are done in gerrit, using a similar workflow to how we review and merge changes to the code itself. For specific policies around specification review, refer to the end of this document.
The layout of this repository is:
Where there are two sub-directories:
specifications approved but not yet implemented
This directory structure allows you to see what we thought about
doing, decided to do, and actually got done. Users interested in
functionality in a given release should only refer to the
The lifecycle of a specification
Developers proposing a specification should propose a new file in the
approved directory. nova-specs-core
will review the change in the usual manner for the OpenStack project,
and eventually it will get merged if a consensus is reached.
At this time the Launchpad blueprint is also "Definition" approved. The developer is then free to propose code reviews to implement their specification. These reviews should be sure to reference the Launchpad blueprint in their commit message for tracking purposes.
The launchpad blueprint's "Definition" approval indicates that the nova-specs-core team agrees with the technical aspects of the proposal ("if we are going to do this, this is how"). The blueprint's "Direction" approval is a separate indication of commitment to the targeted release ("we want to do this now"). It is possible to have a specification and blueprint "Definition" approved, but not have its "Direction" approved due to subsequent planning activities. In such cases, the blueprint (and any unmerged code) could be deferred for consideration in a future release.
Document the specifics of these "planning activities".
Once all code for the feature is merged into Nova, the Launchpad blueprint is marked "Implemented" by a nova maintainer.
At the end of the release cycle, implemented specifications are moved
approved directory to the
directory, creating redirects so that existing links to the approved
specification are not broken. (Redirects aren't symbolic links, they are
defined in a file which sphinx consumes. An example is at
We use the
tox -e move-implemented-specs target at the
end of each release to automatically move completed specs and populate
the redirects file for that release. For example:
tox -r -e move-implemented-specs -- --dry-run --verbose train
--dry-run flag to perform the actual file
moves/writes. Then commit the changes and submit the review to gerrit as
You can find a spec template for a given release in
Additionally, we allow the proposal of specifications that either do not have a developer assigned to them or are not targeted for the current release. These are proposed for review in the same manner as above, but are added to:
Specifications in this directory indicate the original author has
either become unavailable or has indicated that they are not going to
implement the specification. The specifications found here are available
as projects for people looking to get involved with Nova. Alternatively,
they may be for ideas generated during a given release cycle to begin
design discussions, but not intended to be implemented until a future
cycle. If you are interested in claiming an unassigned backlog spec, or
are the assignee and are ready to propose it for implementation in the
current release, start by posting a review for the specification that
moves it from this directory to the next active release. To ensure
existing links are not broken, redirects must be created in a fashion
similar to the process for
implemented specs above. The
move-spec tox target is available to help with this. For
tox -e move-spec -- --dry-run --verbose specs/backlog/my-great-idea.rst specs/train/approved
--dry-run option to perform the actual file
moves/writes. Then commit the changes and submit the review to gerrit as
Please do not use
move-spec to repropose an
unimplemented spec from one release to another. Instead follow the
instructions at Previously
When claiming an unassigned backlog spec, please set yourself as the new primary assignee and maintain the original author in the other contributors list.
Abandoning a specification
For now, this process should only be used to abandon backlog specs.
Please do not use this process for specs in a real release's
approved directory. Currently the indication that such a
spec is abandoned is that it never appears in any release's
implemented directory. We may change this process in the
If it is decided that a
backlog spec is "never" going to
be implemented, post a review moving the specification from
specs/abandoned. As with the above processes, redirects
must be created to ensure existing links are not broken. The
abandon-spec tox target is available to help with this. For
tox -e abandon-spec -- --dry-run --verbose specs/backlog/it-was-a-great-idea.rst
--dry-run option to perform the actual file
Please add an explanation to the spec indicating why it is being abandoned, and update the History section accordingly.
Design documents for releases prior to Juno
Prior to the Juno development cycle, this repository was not used for spec reviews. Reviews prior to Juno were completed entirely through Launchpad blueprints
Please note, Launchpad blueprints are still used for tracking the current status of blueprints. For more information, see https://wiki.openstack.org/wiki/Blueprints
Working with gerrit and specification unit tests
For more information about working with gerrit, see http://docs.openstack.org/infra/manual/developers.html#development-workflow
To validate that the specification is syntactically correct (i.e. get more confidence in the Zuul result), please execute the following command:
tox, the documentation will be available
for viewing in HTML format in the
Specification review policies
There are a number of review policies which nova-specs-core will apply when reviewing proposed specifications. They are:
Proposed changes which are trivial (very small amounts of code) and don't change any of our public APIs are sometimes not required to provide a specification. In these cases a Launchpad blueprint is considered sufficient. These proposals are approved during the Open Discussion portion of the weekly nova IRC meeting. If you think your proposed feature is trivial and meets these requirements, we recommend you bring it up for discussion there before writing a full specification.
Previously approved specifications
Specifications are only approved for a single release. If your specification was previously approved but not implemented (or not completely implemented), then you must seek re-approval for the specification. You can re-propose your specification by doing the following:
- Copy (not move) your specification to the right directory for the current release.
- Update the document to comply with the new template; modify the
History section; select a new
feature liaison <feature-liaisons>if needed.
- If there are no functional changes to the specification (only
template changes) then add the
Previously-approved: <release>tag to your commit message.
- Send for review.
- These specifications are subject to the same review process as any other. They need to be reevaluated to ensure the technical aspects are still valid and that we still wish to implement it given resource constraints and other priorities.
Specifications which depend on merging code in other OpenStack projects
For specifications that depend on code in other OpenStack
projects merging we will not approve the nova specification
until the code in that other project has merged. The best example of
this is Cinder and Neutron drivers. To indicate your specification is in
this state, please use the Depends-On git commit message tag. The
correct format is
Depends-On: <change id of other work>.
nova-specs-core can approve the specification at any time, but it won't
merge until the code we need to land in the other project has merged as
New libvirt image backends
There are some cases where an author might propose adding a new libvirt driver image storage backend which does not require code in other OpenStack projects. An example was the ceph image storage backend, if we treat that as separate from the ceph volume support code. Implementing a new image storage backend in the libvirt driver always requires a specification because of our historical concerns around adequate CI testing.
Write a fleshed-out section on the roles and responsibilities of the nova team, including things like the two +2 rule, the same-company trifecta rule, whether +2ing a spec represents a commitment to review the corresponding code, etc.
Feature Liaison FAQ
In Ussuri, a mandatory "Feature Liaison" section was added to the spec template. This section attempts to address some of the questions around this concept. In Victoria we made filling the section optional but still encourage contributors to use it.
- What does a Feature Liaison do?
By signing up to be a feature liaison for a spec, you're agreeing to help shepherd the feature through the development process. This has different implications depending on the identity/role of the spec owner and your relative roles in the project. Some examples:
- Liaison for an inexperienced contributor: This is the case for which the liaison concept was conceived. In this case the liaison's job is to mentor the spec owner, keep an eye on their progress, let them know when they're missing some obscure (or not-so-obscure) part of the process, help them understand what "review-ready" means, etc. You are also committing to reviewing their code -- or at the very least helping them track down suitable reviewers.
- Designating yourself as your own liaison: If you're a nova core or experienced nova developer, you're already culturally indoctrinated. You know how to navigate the process. You know how to ask for reviews. You still can't +1/+2 your own code.
- Core or experienced nova dev procures separate liaison: Since you don't need the mentorship aspect, your liaison in this case is really just committing to doing reviews. While not necessary, it might be nice to get that kind of commitment up front.
The above is not exhaustive; clearly there is a lot of middle ground between an inexperienced contributor and a nova-core as a spec owner. It should hopefully be fairly obvious how the liaison's role shifts in that middle ground. If further clarification is necessary, please edit this doc.
- Feature Liaison need not be a nova-core.
The role of a liaison does not require +2 powers. A feature liaison should be taken to mean "experienced nova developer capable of doing the job". That said, whereas nova cores implicitly match that description by virtue of having been made cores, non-cores proposed as liaisons should be evaluated on a case-by-case basis (by the reviewers of the spec) as part of the spec review process to determine whether they qualify. For the most part, "we know who you are". (Note that in cases where an experienced non-core is a liaison for someone else's feature, they're still signing up to do reviews, which are still valuable despite maxing out at +1.)
- How do I find a Feature Liaison?
If you do not already have agreement from someone to act as your liaison, note this in your spec draft. You may accelerate the process by communicating with the nova development team on IRC (
#openstack-nova), in a nova IRC meeting, or via the openstack-discuss mailing list.
- What about specless blueprints?
We'll put the name of the feature liaison into the blueprint description. It's not as automatically-enforceable as the template checker, but oh well.
- How does liaison-hood relate to blueprint approval and prioritization?
It really doesn't. If you sign up to be a liaison for blueprint X, the nova team may still decide blueprint X is a nonstarter for technical reasons; or that we don't have the bandwidth to get it done this cycle in light of other priorities. You're really just saying, "If this goes, I'm on it."
- How does liaison-hood relate to the gerrit review for the spec?
A liaison can (and really should, though it's not a hard requirement (yet)) review and +2/+1 a spec for which they're the liaison (but not the owner). However, everyone is still encouraged to review and approve other specs as well (otherwise nothing will get done) (also see below). (It would be nice if an upvote on a spec patch also acted as a commitment to review the corresponding code, but the liaison process does not attempt to address that (yet).)
- Am I still allowed to care about / review / shepherd other approved features for which I didn't volunteer to be a liaison?
Of course. The point of this is the converse: If you don't pay attention to features you did sign up for, people will draw moustaches on pictures of your face. Or horns, if you already have a moustache.