Mutating and validating webhook configuration for API resource

[Amila-Rukshan]

Purpose

This PR is to add MutatingWebhookConfiguration and ValidatingWebhookConfiguration for API CR. Kubebuilder supports scaffolding code for validations.

Adapter exposes an endpoint as a webhook server.

cert-manager has added as dependancy to generate webhook server certs and ca bundle https://book.kubebuilder.io/cronjob-tutorial/cert-manager.html

Since namesapace and name of of the service can change how helm install is done. Using cert manager we can generate cert including the correct service dns name.

Examples

If user do command kubectl apply api.yaml with an already used context then API resource will be rejected with the following error.

The API "webhook-site-2" is invalid: spec.context: Invalid value: "/my-api/7.7.0": an API has been already created for the context: /my-api/7.7.0

References

Implemementing kubebuilder Defaulter and Validator interfaces - https://book.kubebuilder.io/cronjob-tutorial/webhook-implementation.html

k8s admission control - https://kubernetes.io/docs/reference/access-authn-authz/extensible-admission-controllers/#request

Fixes

#319

Notes

No API property defaulting logic is added yet. can implement them in Default method:

func (r *API) Default() {
	// TODO: Add any defaulting logic here
}

[AmaliMatharaarachchi]

What happens if the validation fails? CR creation would get rejected or get created anyway?

[Amila-Rukshan]

yes, resource doesn't get created in etcd as k8s server rejects with the error. User can see the error in the console.