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


implemented specifications

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 implemented directory.

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 from the approved directory to the implemented 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 specs/stein/redirects.)

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

Remove the --dry-run flag to perform the actual file moves/writes. Then commit the changes and submit the review to gerrit as usual.

Example specifications

You can find a spec template for a given release in specs/<release>-template.rst.

Backlog specifications

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 example:

tox -e move-spec -- --dry-run --verbose specs/backlog/my-great-idea.rst specs/train/approved

Remove the --dry-run option to perform the actual file moves/writes. Then commit the changes and submit the review to gerrit as usual.


Please do not use move-spec to repropose an unimplemented spec from one release to another. Instead follow the instructions at Previously approved specifications

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 future.

If it is decided that a backlog spec is “never” going to be implemented, post a review moving the specification from specs/<release>/approved to 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 example:

tox -e abandon-spec -- --dry-run --verbose specs/backlog/it-was-a-great-idea.rst

Remove the --dry-run option to perform the actual file moves/writes.

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

Working with gerrit and specification unit tests

For more information about working with gerrit, see

To validate that the specification is syntactically correct (i.e. get more confidence in the Zuul result), please execute the following command:

$ tox

After running tox, the documentation will be available for viewing in HTML format in the doc/build/html/ directory.

Specification review policies

There are a number of review policies which nova-specs-core will apply when reviewing proposed specifications. They are:

Trivial specifications

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 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 well.

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.