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Knative release principles
Knative Release Principles
These principles are forward looking from release 0.13.x onward. There are plenty of examples where some or all of these principles have not been followed in the past. We are not looking to change past behavior, but to help define future behavior for the project.
† - Some things may not be possible due to either the maturity of CRDs or the mechanism by which they are implemented (e.g. not an API Server, no conversion webhooks, bugs).
K8s minimum version principle:
We (the community) support the range of upstream minor Kubernetes versions that are Kubernetes community supported at the time of the cut. Only the latest patch release of the minor version is tested for support. Support for versions prior to that are best effort, or by vendors.
Adoption of newer K8s minimum versions will also be on a best-effort basis. When a Kubernetes version is released it’s availability in downstream distributions is often lagging. When these delays affect our planned min K8s version we’ll update the version table below and make it known in the release’s notes.
This principle will be revisited when changes to upstream Kubernetes support policy occur.
Knative community support window principle:
We (the community) support the most recent 4 versions of Knative. The term support as used here means that we will maintain release branches for these releases. We will consider backporting applicable fixes to these release branches depending on severity and feasibility.
Default and optional API versions principle:
There will be at least one common API version available across all community supported versions (See Community support window principle) at any given time. At least one of these common API versions will be enabled by default from the open source installation path. The open source installation process may allow optional API versions at the discretion of the installing user.
API Support Principle:
We (the community) support all API versions (both default and optional) available from current community supported Knative releases. We will keep Beta API versions available in releases for at least 9 months and GA API versions in releases for at least 12 months after deprecation is announced. Earlier API versions are best effort, or by vendors. See FAQ for v1alpha1.
Recommended API version principle:
We (the community) recommend that clients developing to a static API version (including non-versioned tests) develop to the highest common API version offered across supported community releases at the time of development. Where feasible a dynamic client should be preferred.
Example: If 0.8.x through 0.11.x are the current community supported versions then v1alpha1 would be the recommended client version as 0.8.x does not support v1beta1 nor v1 by default. This makes v1alpha1 the common version. (Note: This would mean 0.11.x must support v1alpha1 by default otherwise we do not have any minimum overlapping version).
Runtime Conformance Principle:
In order to be runtime conformant for a given release, an installation must pass the runtime conformance tests for the installed version and 3 prior versions (as determined by the supported version principle). This means runtime tests for a given version should follow the recommended API version principle to be forwards compatible when run against one of the 3 subsequent versions.
API Conformance Principle:
In order to be API conformant for a given release, an installation must pass conformance for the installed version and 3 prior versions for common API versions. There will always be at least one such version due to the principles above.
Project, Feature, and Sub-Feature Phase Principle:
There will be a phase identified for each project, feature, and sub-feature for each release. Each of the phases: Alpha, Beta, and Stable will have clear definitions related to performance, deprecation and maintenance.
|Purpose||Works with possible limitations||Works end to end||Production Ready|
|API||May not be backward compatible||Versioned, may not be backward compatible||Versioned / Backward Compatible|
|Performance||No guarantee||No guarantee - Baseline||Performance is quantified, documented, and guarantees against regression|
|Deprecation Notice||none||9 months||12 months|
What happens during upgrades of Knative?
We support upgrading versions of Knative from any community supported version of Knative to a minor version one higher. Upgrade steps larger than one minor version must go through an intermediate version first. As an example, if the current community versions are 0.9.x through 0.12.x the upgrade matrix will look like below:
|Knative Version||Upgrades to|
What happens during downgrades of Knative?
Knative downgrades are a harder story than upgrades as the purpose of the upgrades are to fix bugs and add features. That said there are many cases where a downgrade or rollback is appropriate. As downgrades are more difficult to get right Knative will make a best effort to support downgrade of a single minor version and only if users have not already taken advantage of new features or fields.
This means that we need to support the downgrade tests case within our project to ensure that downgrade is indeed possible before code checked in and releases are cut.
What happens during upgrades of Kubernetes?
Strawman: Upgrading Kubernetes may move you from a Kubernetes version for which a release was intended to a newer version that may have not been originally qualified. We expect this to work given Kubernetes backwards compatibility support. We intend for these upgrades to be a non-issue. If particular versions are found to be incompatible and the Knative version is still community supported we will either:
- work with the Kubernetes community on a fix or
- develop a patch release to workaround the issue. We will publish guidance on potential incompatibility on knative.dev
Which API endpoints should I enable when I vend/host Knative Serving?
Vendors may make their decisions about supporting API versions. They may decide to support optional API versions by default or may support API versions that are EOL in the open source community. The recommendation of the community is to offer all APIs versions that the Open Source project makes available by default for a given release version. This offers clients the best interoperability and users the best portability.
What about Serving v1alpha1 API support?
Due to the length of time we have supported v1alpha1, the ubiquity of availability across released Knative Serving versions, and the presence of clients statically developed against this version we will treat the current set of v1alpha1 Serving APIs as ‘Beta’ APIs. This means that we will keep v1alpha1 available in releases for at least 9 months after deprecated is announced. During that period of time of availability, we will evaluate whether the API is available through the default Open Source installation by following the Default and optional API versions principle.
What happens when the minimum Kubernetes version for a supported Knative release is no longer supported by Kubernetes?
We will explicitly avoid introducing changes into a Knative Serving release branch that would raise the minimum version. We will not keep around test clusters for unsupported Kubernetes versions, but we will attempt to solve user reported bugs to the best of our ability.
Can we have the table below on knative.dev?
Yes. We will publish a table similar to below once we have agreement on the principles so that users can easily determine versions and endpoints available for a given release.
Knative Version Tables
See RELEASE-SCHEDULE for this information. We’re working to make the current information API-consumable as well.
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