How do I programtically validate a go structure that has kubebuilder validation markers?

[stack123-afk]

Say I have the following structure:

type ToySpec struct {
    // +kubebuilder:validation:MaxLength=15
    // +kubebuilder:validation:MinLength=1
    Name string `json:"name,omitempty"`
}

I wanna do something like this:

spec  = ToySpec{Name: ""}
err := Validate(spec) // Should return error as  name has length of 0

Is this currently possible?

[camilamacedo86]

Hi @stack123-afk,

When you use markers like +kubebuilder:validation:MaxLength and +kubebuilder:validation:MinLength (see markers reference), running make manifests triggers controller-gen, which generates your CRD (CustomResourceDefinition) with OpenAPI schema validation.

This validation is enforced by the Kubernetes API server when you create or update resources via the API. For instance, when you run kubectl apply -f sample_cr.yaml, the API server checks the resource against these validations. If the resource doesn't meet the validation criteria, the operation will fail.

However, if you want to validate the spec/CR during reconciliation in your controller or directly within your Go code, you'll need to implement this validation manually in the controller's reconcile loop or by using webhooks.

Here's an example of how you can implement this validation in Go, such as:

func (spec *ToySpec) Validate() error {
    if len(spec.Name) < 1 {
        return errors.New("name is too short ... must be >= 1")
    }
    if len(spec.Name) > 15 {
        return errors.New("name is too long... It must be <= 15")
    }
    return nil
}

Also, you can consider to do validations using WebHooks (https://book.kubebuilder.io/reference/webhook-overview), i.e.:

kubebuilder create webhook --group --version --kind --programmatic-validation

Also, see: https://book.kubebuilder.io/cronjob-tutorial/webhook-implementation

And see that the docs are using methods which are deprecated in the controller-runtime, so if you decide to use webhooks, I would suggest you follow the approach of the PR: #4060

The proposed changes in the docs done in this PR: https://github.com/kubernetes-sigs/kubebuilder/pull/4061/files also might be helpful for you understand it.

By last, if you do not understand the concept of the reconcile I would recommend you ensure that you read the Getting Started at least: https://book.kubebuilder.io/getting-started (30 min) and https://book.kubebuilder.io/cronjob-tutorial/gvks

I hope that helps you out.
I am closing this one as sorted out. Feel free to raise new issues if you need to.