ClusterNetwork should be optional

[chuckha]

/kind bug

What steps did you take and what happened:
ClusterNetwork on v1a1.Cluster object is required but nothing else is. Is there a reason this is required and not defaulted? kubeadm can probably provide some sane defaults for these values.

What did you expect to happen:
defaulting the cluster network fields.

Anything else you would like to add:

[detiber]

I see no issues with providing defaulting for this, the question would be how to do it. There are potentially 2 different ways:

• webhook
  • this would require no changes to the types themselves
  • adding the default would not trigger an additional reconciliation
• updating the types to allow for omitempty
  • could add the default in the cluster controller, this would trigger an additional reconciliation
  • could allow to remain empty, but would require any places that would consume this value to know handle applying a default.

[vincepri]

/area api

[davidewatson]

I think kubeadm does default these values. I put up a PR a while back to make this field optional: #919

[detiber]

kubeadm does indeed default these values. That said, this goes a bit beyond just bootstrapping, as it would also impact the CNI configuration as well.

[vincepri]

Closing now that #919 has been merged