Return an emulated etcd version in the status endpoint

[sambhav]

Fixes #315

See /~https://github.com/kubernetes/kubernetes/blob/beb696c2c9467dbc44cbaf35c5a4a3daf0321db3/staging/src/k8s.io/apiserver/pkg/storage/feature/feature_support_checker.go#L157

Which expects that the etcd status endpoint return a version. This returns a default version allowing users to override it if necessary.

[brandond]

LGTM, with a few nits

An additional question: if we fix the version reporting, Kubernetes will try to use watch progress notifications. However, Kubernetes also requires you to set the --experimental-watch-progress-notify-interval=5s (instead of the default of 10m) when using watch progress notifications. This is also true when using kine; it has the same default value for the --watch-progress-notify-interval flag as upstream etcd.

Would you mind modifying the markdown files in the examples folder to call this out, and show the flag being set?

[sambhav]

@brandond would you be open to changing the default value to 5s?

[brandond]

Yeah, I can't see how it would hurt anything. K3s already sets it to 5 seconds, for both etcd and kine, so that things work right. I'm kinda curious why etcd didn't change the default as well, given that kubernetes will behave oddly if you don't.

[sambhav]

@brandond all comments should be addressed. Could you also release a new version with these changes once the PR is merged?

[sambhav]

Note, I also added the following comment kubernetes/kubernetes#122805 (comment)