Enable parallel image pulls

[yankcrime]

As of 1.27, Kubernetes added support for parallelizing image pulls but this is not enabled by default. This is especially useful in situations where multiple images need to be downloaded to a host, but one of them is particularly large.

[yankcrime]

@spjmurray Happy to be debate what in this PR should be configurable, and where.

[spjmurray]

ew... erm, is there any benefit in having this on the CP nodes too? May make start up marginally faster

[spjmurray]

And that answers my next question....

[Tue  5 Nov 12:35:12 GMT 2024] simon@symphony ~/src/github.com/kubernetes/kubernetes make all WHAT=cmd/kubelet
+++ [1105 12:35:36] Building go targets for linux/amd64
    k8s.io/kubernetes/cmd/kubelet (non-static)
[Tue  5 Nov 12:35:38 GMT 2024] simon@symphony ~/src/github.com/kubernetes/kubernetes ./_output/bin/kubelet --help | grep serialize
      --serialize-image-pulls                                    Pull images one at a time. We recommend *not* changing the default value on nodes that run docker daemon with version < 1.9 or an Aufs storage backend. Issue #10959 has more details. (default true) (DEPRECATED: This parameter should be set via the config file specified by the Kubelet's --config flag. See https://kubernetes.io/docs/tasks/administer-cluster/kubelet-config-file/ for more information.)

[yankcrime]

Given we pre-pull images necessary for bootstrap, I'd say probably not.

[spjmurray]

Cilium, occm, blah? I don't see the harm.

[spjmurray]

For future reference see here: https://github.com/kubernetes/kubernetes/blob/release-1.31/staging/src/k8s.io/kubelet/config/v1beta1/types.go#L89

[spjmurray]

You know what, I think it'll make life easier for the whole world if we just say...

values.yaml

workloadPools:
  kubelet:
    serializeImagePulls: "false"
    foo:
      bar: sheep
      baz: ball

Then go something like...

{{- with $config := .Values.workloadPools.kubelet }}
{{- $_ := set $config "apiVersion" "kubelet.config.k8s.io/v1beta1" -}}
{{- $_ := set $config "kind" "KubeletConfiguration" -}}
...
content: {{ toJson $config }}
{{- end }}

Then you can inject anything ever without another modification just using --set

[spjmurray]

I'd check with multiple pools first though in case the config is mutated in place and you get multiple instances of the apiVersion and kind. There's probably a deep copy/clone somewhere in sprig.

[spjmurray]

This doesn't actually work when you test it...

Needs to be

{{- with ... -}}
{{- $_ := ... -}}
{{- $_ := ... }}

please note the trailing whitespace chomping, otherwise you get

      - path: /etc/kubernetes/patches/kubeletconfiguration0+strategic.json
        owner: "root:root"
        permissions: "0644"content: {"apiVersion":"kubelet.config.k8s.io/v1beta1","foo":"bar","kind":"KubeletConfiguration"}

[spjmurray]

What happens when you provision something with no content? I can see...

        // Content is the actual content of the file.
        // +optional
        Content string `json:"content,omitempty"`

So the content itself is optional, I just dunno if kubeadm is gonna crap out with an empty patch file. Talk to me Goose!