nova/doc/source/feature_classification.rst

Feature Classification

This document aims to define how we describe features listed in the support-matrix.

Aims

Our users want the features they rely on to be reliable and always continue to solve for their use case. When things break, users request that we solve their issues quickly. It would be better if we never had those regressions in the first place.

We are taking a two-pronged approach:

• Tell our users what features are complete, well-documented, and are kept stable by good tests. They will get a good experience if they stick to using those features. Please note that the tests are specific to particular combinations of technologies. A deployment's choice of storage, networking and hypervisor makes a big difference to what features will work.
• Get help for the features that are not in the above state, and warn our users about the risks of using those features before they are ready. It should make it much clearer how to help improve the feature.

Concepts

Some definitions to help understand the later part of the document.

Users

These are the users we will talk about in this document:

• application deployer: creates/deletes servers, directly or indirect via API
• application developer: creates images and apps that run on the cloud
• cloud operator: administers the cloud
• self service administrator: both runs and uses the cloud

Now in reality the picture is way more complex. Specifically, there are likely to be different roles for observer, creator and admin roles for the application developer. Similarly, there are likely to be various levels of cloud operator permissions, some read only, see a subset of tenants, etc.

Note: this is not attempting to be an exhaustive set of personas that consider various facets of the different users, but instead aims to be a minimal set of users, such that we use a consistent terminology throughout this document.

Feature Group

To reduce the size of the matrix, we organize the features into groups. Each group maps to a set of user stories, that can be validated by a set of scenarios, tests. Typically, this means a set of tempest tests.

This list focuses on API concepts like attach and detach volumes, rather than deployment specific concepts like attach iSCSI volume to KVM based VM.

Deployment

A deployment maps to a specific test environment. A full description of the environment should be provided, so its possible to reproduce the test results that are reported for each of the Feature Groups.

Note: this description includes all aspects of the deployment: the hypervisor, the number of nova-compute services, the storage being used, the network driver being used, the types of images being tested, etc.

Feature Group Maturity

The Feature Group Maturity rating is specific to the API concepts, rather than specific to a particular deployment. That detail is covered in the deployment rating for each feature group.

We are starting out these Feature Group ratings:

• Incomplete
• Experimental
• Complete
• Complete and Required
• Deprecated (scheduled to be removed in a future release)

Incomplete features are those that don't have enough functionality to satisfy real world use cases.

Experimental features should be used with extreme caution. They are likely to have little or no upstream testing. With little testing there are likely to be many unknown bugs.

For a feature to be considered complete, we must have:

• Complete API docs (concept and REST call definition)
• Complete Administrator docs
• Tempest tests that define if the feature works correctly
• Has enough functionality, and works reliably enough to be useful in real world scenarios
• Unlikely to ever have a reason to drop support for the feature

There are various reasons why a feature, once complete, becomes required, but currently its largely when a feature is supported by all drivers. Note that any new drivers need to prove they support all required features before it would be allowed in upstream Nova. Please note that this list is technically unrelated to the DefCore effort, despite there being obvious parallels that could be drawn.

Required features are those that any new technology must support before being allowed into tree. The larger the list, the more features can be expected to be available on all Nova based clouds.

Deprecated features are those that are scheduled to be removed in a future major release of Nova. If a feature is marked as complete, it should never be deprecated. If a feature is incomplete or experimental for several releases, it runs the risk of being deprecated, and later removed from the code base.

Deployment Rating for a Feature Group

The deployment rating is purely about the state of the tests for each Feature Group on a particular deployment.

There will the following ratings:

• unknown
• not implemented
• implemented: self declare the tempest tests pass
• regularly tested: tested by third party CI
• checked: Tested as part of the check or gate queue

The eventual goal is to automate this list from some third party CI reporting system, but so we can make progress, this will be a manual inspection that is documented by an hand written ini file. Ideally, this will be reviewed every milestone.

Feature Group Definitions

This is a look at features targeted at application developers, and the current state of each feature, independent of the specific deployment.

Please note: this is still a work in progress!

Key TODOs:

• use new API docs as a template for the feature groups, into ini file
• add lists of tempest UUIDs for each group
• link from hypervisor support matrix into feature group maturity ratings
• add maturity rating into the feature groups, with a justification, which is likely to include lints to API docs, etc
• replace tick and cross in support matrix with "deployment ratings"
• eventually generate the tick and cross from live, historical, CI results