Can you rename this to ExtraAPIServerArgs map[string]string?

Also

ExtraAPIServerArgs map[string]string `json:"extraAPIServerArgs"`

I think this can move to constants.go

could you do this instead here:

for k, v := range cfg.ExtraAPIServerArgs {
    command = append(command, fmt.Sprintf("--%s=%s", k, v))
}
// These arguments are defaults that can be overridden by ExtraAPIServerArgs
configurableDefaultCommands := map[string]string{
    "admission-control": kubeadmconstants.DefaultAdmissionControl,
    "insecure-bind-address": "127.0.0.1",
    "allow-privileged": "true",
}
for k, v := range configurableDefaultCommands {
    if _, overrideExists := cfg.ExtraAPIServerArgs[k]; !overrideExists {
        command = append(command, fmt.Sprintf("--%s=%s", k, v))
    }
}

the logic I outlined here should probably be a separate function that takes cfg.ExtraAPIServerArgs and configurableDefaultCommands as inputs and outputs a []string

I would name this "APIServerExtraFlags"

Put API server first so that as we have other stuff it sorts.

Flags explains why it is a map. Still not clear how to do singleton flags or remove flags but I think that is okay.

Also, we should start documenting these structures (ala types.go everywhere else). Explain that this is a way to add and override flags that get set on the API server.

For things like the admission controller this still isn't 100% as there is no way to add/remove/modify the list. But it is good enough to get started for now and at least it is possible to modify this stuff.

Might also be good to support this for the KCM and the scheduler. But that can come in other PRs.

Why not let users override all of this?

Yes, let's rename this to defaultArguments or similar

Are we going to turn this off at some point?

Yes, let's rename this to defaultArguments or similar

This func can be removed

This should be a standalone function that takes two params: defaults and overrides. The logic could/should look something like this:

command := []string{}
for k, v := range overrides {
   command = append(command, fmt.Sprintf("--%s=%s", k, v))
}
for k, v := range defaults {
    if _, overrideExists := overrides[k]; !overrideExists {
         command = append(command, fmt.Sprintf("--%s=%s", k, v))
    }
}

it just takes what's in overrides right away and appends the rest of the defaults that don't exist already

There must be an unit test for that function

Please add a similar field for the scheduler and controller-manager and implement this for them as well.
Due to the code freeze, we must get this today/tomorrow or wait a month.

Comments would be appreciated but I wouldn't block on that

Please add the controller-manager and scheduler args here as well

please make all args configurable and call them just defaultArguments, same for controller-manager and scheduler

this becomes unnecessary when having only one map of defaults

Many thanks for fixing this. Has been annoying but haven't got to fixing it 👍