kubeadm upgrade docs

[mhausenblas]

This is a...

• Feature Request
• Bug Report

Problem:

When kubernetes/kubernetes#48899 lands we want docs for it.

Proposed Solution:

Write some end-user facing docs/walkthroughs for kubeadm upgrade.

Page to Update:
New page? Not sure where to put it.

[luxas]

Sounds good to me to do this proactively! :)
I'd be happy with having you write a WIP PR for this early on based on some runs with a binary from my fork (I can provide one easily for you)

The sooner we start to write docs, the better. Often this is left to the last minute, which is a bad habit.

[mhausenblas]

Awesome, yes, let's do it. Please advise for a starting point @luxas …

[castrojo]

The first step has the user curling a kubeadm binary. I asked if just waiting for the kubernetes repo to be updated to 1.8 and running the packaged version would work:

luxas: Problem statement: an `apt-get upgrade` before pulls down a new kubelet for an old API, which is not supported
jorge: that sounds like it would actually break
luxas: Yes
luxas: hence we need to do CLI only first, upgrade the control plane, and then upgrade the node
lucas: updating the _kubeadm deb_ would reconfigure the kubelet to become unresponsive as well :disappointed:

Perhaps we should be more explicit in telling the user that they need to get the kubeadm binary out of band first and NOT just do an apt update/dist-upgrade even though kubeadm 1.8 will be sitting in the repo.

[luxas]

@castrojo Feel free to improve the wording of the guide :)