Revisit: K8s minimum version principle

[mattmoor]

See here: https://kubernetes.io/blog/2020/08/26/kubernetes-release-1.19-accentuate-the-paw-sitive/#increase-kubernetes-support-window-to-one-year

cc @dprotaso @pmorie

[mattmoor]

@dprotaso do you want to take a crack at this now that you're back? 🥺

[dprotaso]

yeah it's on my backlog

[evankanderson]

(ping)

[dprotaso]

related: kubernetes/sig-release#1290

[dprotaso]

And https://github.com/kubernetes/sig-release/blob/master/releases/patch-releases.md

[dprotaso]

woo structured data https://github.com/kubernetes/sig-release/blob/master/releases/schedule.yaml

[dprotaso]

Recap: 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.

Upstream EOL Changes

With v1.19 the support window is now a year. This change has been rolled back into v1.17 & v1.18 (see PR).

Current Version Pairing between K8s & Knative

Knative	Min K8s	notes
v0.19	v1.17
v0.20	v1.17	EOLs 2 weeks after
v0.21	v1.18
v0.22	v1.18	EOLs 2 weeks after
v0.24	v1.19
v0.25	v1.19
v0.26	v1.19	EOLs 1 week after
v0.27	v1.20

Here's an interactive sheet showing and an image for the lazies

Recommendation

I suggest we include a clause specifying that K8s releases with an upcoming EOL will be skipped.

We (the community) support the range of upstream minor Kubernetes versions that are Kubernetes community supported at the time of the cut excluding versions with an upcoming end-of-life date. 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.
...

What we should decide is what the cut-off should be - ie. if EOL date is <= 2 months away then skip

[evankanderson]

@markusthoemmes to find the right person to look at this, maybe @pmorie ?