add auto_calculation for system_reserved resources

[Payback159]

What type of PR is this?

Uncomment only one /kind <> line, hit enter to put that in a new line, and remove leading whitespaces from that line:

/kind api-change
/kind bug
/kind cleanup
/kind design
/kind documentation
/kind failing-test

/kind feature

/kind flake

What this PR does / why we need it:

Reserving resources helps to improve the stability of the cluster components. In my opinion, the resource consumption of the system also changes with the load of the node (Scheduled Pods), so there should also be a possibility to reserve the system resources relative to the node size.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Calculation was copied from here: https://cloud.google.com/anthos/clusters/docs/on-prem/latest/how-to/resources-available-pods I have added a new variable system_reserved_auto_calculate so that Kubespray users can decide whether they want to use the automatic calculation or assign absolute values.

Does this PR introduce a user-facing change?:

NONE

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[Payback159]

I am currently considering whether we should take this as an opportunity to rename the system_master* variables to system_control_plane*. This would lead to a user-facing change but it should be done either way or what do you think?

[VannTen]

I am currently considering whether we should take this as an opportunity to rename the system_master* variables to system_control_plane*. This would lead to a user-facing change but it should be done either way or what do you think?

the *_master and *_node variable needs to go anyway, they are redundant with group_vars. I'm overhauling that part (cgroups / reserved stuff) in #10714

[VannTen]

Besides that, what system components do you think scale their resources usages with number of scheduled pods exactly ?
For kube_reserved (aka container manager + kubelet) I can see, but for system_reserved that's less obvious: sshd and similar don't depend on the number of scheduled pods.
I could see the kernel + maybe the network manager ?

[Payback159]

@VannTen you are completely right. I confused it with kube-reserved as I was thinking about necessary file-handler and additional load on the kubelet agents, container runtime per pod/container.

If you agree with me I would like to adapt the PR to provide the logic for kube-reserved. For system-reserved it makes less sense to me, as these should correlate less strongly with the load.

[yankay]

/ok-to-test

[k8s-ci-robot]

@Payback159: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubespray-yamllint	91a1645	link	true	/test pull-kubespray-yamllint

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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[VannTen]

... I would like to adapt the PR to provide the logic for kube-reserved.

Fine by me.

Another remark: it would a good idea to document (and links to in the best case) the calculation method used. (that would make it easier to see if we could change it in the future in particular).

[Payback159]

Hello @VannTen,

with a little delay I have now placed a new PR for kubeReserved values. I am closing this PR as it will become obsolete.

#11082

I have added the documentation about the calculation to the cgroup documentation as it makes the most sense to me.