Kubernetes Custom Resources (CRD) Tutorial

Tutorial for building Kubernetes Custom Resources (CRD) extensions you can see the full tutorial documentation in: The New Stack

Note: CustomResourceDefinition (CRD) is the successor of the deprecated ThirdPartyResource.

this example is based on Kubernetes apiextensions-apiserver example

Organization

the example contain 3 files:

• crd - define and register our CRD class
• client - client library to create and use our CRD (CRUD)
• kube-crd - main part, demonstrate how to create, use, and watch our CRD

Running

# assumes you have a working kubeconfig, not required if operating in-cluster
go run *.go -kubeconf=$HOME/.kube/config

kube-crd

kube-crd demonstrates the CRD usage, it shoes how to:

1. Connect to the Kubernetes cluster
2. Create the new CRD if it doesn't exist
3. Create a new custom client
4. Create a new Example object using the client library we created
5. Create a controller that listens to events associated with new resources

The example CRD is in the following structure:

type Example struct {
      meta_v1.TypeMeta   `json:",inline"`
      meta_v1.ObjectMeta `json:"metadata"`
      Spec               ExampleSpec   `json:"spec"`
      Status             ExampleStatus `json:"status,omitempty"`
}
type ExampleSpec struct {
      Foo string `json:"foo"`
      Bar bool   `json:"bar"`
      Baz int    `json:"baz,omitempty"`
}

type ExampleStatus struct {
      State   string `json:"state,omitempty"`
      Message string `json:"message,omitempty"`
}

• The Metadata part contain standard Kubernetes properties like name, namespace, labels, and annotations
• The Spec contain the desired resource configuration
• The Status part is usually filled by the controller in response to Spec updates