Add way to specify kubeadm's --ignore-preflight-errors in InitConfiguration and JoinConfiguration

[marccarre]

What would you like to be added:

A single way to configure all of kubeadm's behaviour.
In particular, given ignorePreflightErrors and externalcfg are currently disjoint:

• https://github.com/kubernetes/kubernetes/blob/a887ae8344adf9739c1d156a718c05fdf95b73ab/cmd/kubeadm/app/cmd/init.go#L104-L106
• https://github.com/kubernetes/kubernetes/blob/a887ae8344adf9739c1d156a718c05fdf95b73ab/cmd/kubeadm/app/cmd/join.go#L132-L133

I would like a way to specify the set of strings corresponding to --ignore-preflight-errors's value as an "array" in (at least) InitConfiguration and JoinConfiguration.

Why is this needed:

This would simplify programmatic usage of kubeadm: one configuration file to generate, and then pass to kubeadm.

Potential way forward:

1. Keep --ignore-preflight-errors for backward-compatibility (for now).

2. Add the following field to both InitConfiguration and JoinConfiguration:

   IgnorePreflightErrors []string `json:"ignorePreflightErrors,omitempty"`

3. Take the union of both sets, validate it (as currently done), and use this going in the rest of the program.

Misc.:

Happy to make the change myself, once I get a "go" (or at least, no "no-go") from someone more knowledgeable. (Maybe @luxas? 🙂 )

/kind feature
/sig cluster-lifecycle

[fabriziopandini]

@marccarre fyi yesterday, in the kubeadm office hours was discussed planning for v1.15
There is a batch of changes for the config (including this), and there will be a deep dive hopefully next week. If you want to join the discussion you are more than welcome!

[fabriziopandini]

Fyi #1439