Document that minikube with kubeadm needs 2 CPUs

[afbjorklund]

Eventually this also needs better validation, both for none and for docker driver.

This is supposed to be synced with the information https://kubernetes.io/docs/setup/production-environment/tools/kubeadm/install-kubeadm/#before-you-begin

2 GB or more of RAM per machine (any less will leave little room for your apps)
2 CPUs or more

The memory size is a little misleading (since it uses 2200M, not 2048M) but is not about cpus.
And we accept both 1GB (with a warning, and probably swap) and 2000 without any complaint.

For #6961 #7445 #7782 #7907 #7850 #8045

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: afbjorklund

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• OWNERS [afbjorklund]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov-io]

Codecov Report

Merging #8049 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #8049   +/-   ##
=======================================
  Coverage   35.76%   35.76%           
=======================================
  Files         143      143           
  Lines        9191     9191           
=======================================
  Hits         3287     3287           
  Misses       5504     5504           
  Partials      400      400           

[priyawadhwa]

Nice!

[afbjorklund]

It's a little confusing terminology, like "do you mean 2 cores ? or 2 sockets ? or 2 vCPU"
But better keep it same as upstream (2 CPUs). We just mean two threads, I think ?

Similarly, I'm not sure if it means 2000 MB or 2048 MB. Or should that be "mebibytes" ?
You're supposed to spell it "2 GiB", but who does that. And the KVM translation is off...

But what we do want to avoid is an error, later on.

Range of CPUs is from 0.01 to 1.00, as there are only 1 CPUs available.

[ERROR NumCPU]: the number of available CPUs 1 is less than the required 2

So let's use the term CPUs, it's what everyone is using.

[afbjorklund]

And fortunately Docker allocates 2 vCPUs for their VM, by default. (see #7980)

So that means we only have problems with the memory, not with the CPUs.