Kubeadm: Improve UX for upgrade node experimental-control-plane

[fabriziopandini]

https://github.com/kubernetes/kubernetes/pull/66973 implemented upgrade for secondary instances of the control plane via the new command kubeadm upgrade node experimental-control-plane.

This approach isolates the alpha feature from the main kubeadm workflows, but gives extra works to the users.

Once join --control-plane became not experimental we should review the approach to upgrades as well, perhaps detecting and triggering automatically upgrade of secondary instances of the control plane as a step of a comprehensive kubeadm upgrade node action

See this comments on the PR for more background

[timothysc]

/assign @liztio

[timothysc]

Thanks for filing @fabriziopandini

[timothysc]

@fabriziopandini can we close?

[fabriziopandini]

No. Users are still required to do two actions for upgrading control-plane nodes ATM

[MalloZup]

@fabriziopandini i will take this one.

[fabriziopandini]

kk
/lifecycle active

[yuexiao-wang]

I will take this issue this week after talking with @MalloZup

[fabriziopandini]

@yuexiao-wang when do you plan to send PR for this issue (I'm updating state for Tracking issue for Certificates copy for join --control-plane)

[fabriziopandini]

@yuexiao-wang as discussed in slack we are punting this to v1.15 because HA will not make beta in V1.14

[yuexiao-wang]

Got it

[fabriziopandini]

/lifecycle active
@timothysc @neolit123 @yago @ereslibre @rosti

For upgrades on nodes now we have two commands now:

1. kubeadm upgrade node config to be run on all nodes
2. kubeadm upgrade node experimental-control-plane to be run on control-plane nodes only

My proposal is to:
a. Merge the two commands into kubeadm upgrade node, implementing it as a command with two phases, kubelet-config and control-plane
c. Deprecate 1. (subject to GA constraints), pointing users to use a. (or a. phase)
b. Remove 2. (or deprecate as for 1.) (edited)

CONS: for a transitory period we will have kubeadm upgrade node command with phases subcommand + the olds config / experimental-control-plane deprecated subcommands, that is kind of weird

[neolit123]

i was thinking that we should punt the upgrade phases work to 1.16.
but if you think otherwise, it's fine.

[neolit123]

this seems to be done. upgrade phases for "apply" has a separate ticket.
please reopen if needed.