klog flag deprecation: clarify scope and timeline

Deprecating the flags only in some binaries is not going far enough because the
full feature set would still have to be supported for the remaining ones. The
goal was to remove them everywhere and the KEP gets updated to reflect that.

Because of the deprecation period for command line flags we want to announce
the intent to deprecate as soon as possible. The proposal is to do it already
at the alpha stage in Kubernetes 1.23. Most of the work is done or can be
completed.

Depending on the interpretation of "must function for 2 releases after their
announced deprecation" (does that include the release for which the announcement
was made?) we might be able to remove in 1.25. But to be safe and also to
ensure the "for 12 months" rule, we aim for removal in 1.26.

Author: pohly

keps/sig-instrumentation/2845-deprecate-klog-specific-flags-in-k8s-components/README.md

@@ -124,10 +124,11 @@ best practices.
 
 ## Proposal
 
-I propose to remove klog specific feature flags in Kubernetes core components
-(kube-apiserver, kube-scheduler, kube-controller-manager, kubelet) and leave
-them with defaults. From klog flags we would remove all flags besides "-v"
-and "-vmodule".
+We propose to remove klog specific feature flags in Kubernetes components
+(including, but not limited to, kube-apiserver, kube-scheduler,
+kube-controller-manager, kubelet) and leave them with defaults. From klog flags
+we would remove all flags besides "-v" and "-vmodule". The component-base
+"-log-flush-frequency" flag is also kept.
 
 ### Removed klog flags
 
@@ -269,17 +270,20 @@ all existing klog features.
 
 #### Alpha
 
-- Klog can be configured without registering flags
-- Kubernetes logging configuration drops global state
+- The remaining supported klog options (`-v`, `--vmodule`) and
+  `--log-flush-frequency` can be configured without registering flags.
+- Kubernetes logging configuration is completely stored in one struct
+  (`LoggingConfiguration`) before being applied to the process.
 - Go-runner is feature complementary to klog flags planned for deprecation
 - Projects in Kubernetes Org are migrated to go-runner
 - JSON logs format splits stdout and stderr logs
+- The klog flags which will be removed are marked as deprecated in command line
+  help output and the deprecation is announced in the Kubernetes release notes.
 
 #### Beta
 
 - Go-runner project is well maintained and documented
 - Documentation on migrating off klog flags is publicly available
-- Kubernetes klog flags are marked as deprecated
 
 #### GA
 
@@ -290,6 +294,12 @@ all existing klog features.
 - 20/06/2021 - Original proposal created in https://github.com/kubernetes/kubernetes/issues/99270
 - 30/07/2021 - KEP draft was created
 - 26/08/2021 - Merged in provisional state
+- 09/09/2021 - Merged as implementable
+- Kubernetes 1.23 (tenatative): alpha, [deprecation
+  period](https://kubernetes.io/docs/reference/using-api/deprecation-policy/#deprecating-a-flag-or-cli)
+  starts
+- Kubernetes 1.24 (tentative): beta
+- Kubernetes 1.26 (tentative): GA, deprecated flags get removed
 
 ## Drawbacks
 
@@ -474,4 +484,4 @@ No
 
 ###### What steps should be taken if SLOs are not being met to determine the problem?
 
-N/A
+N/A