How do you create and retrieve Custom Kubernetes Resources using Go?

Creating and Retrieving Custom Kubernetes Resources with Go

Introduction:

Custom Kubernetes resources extend the functionality of the Kubernetes API to manage application-specific objects. This article demonstrates how to create and retrieve custom resources in Go, a commonly used programming language for Kubernetes development.

Creating a Custom Resource

To create a custom resource, you need to:

1. Define the Custom Resource Definition (CRD):

   • Create a YAML or JSON file defining the schema, validation rules, and other metadata for your custom resource.
   • Apply the CRD using kubectl or the Kubernetes API.

2. Implement the resource's logic in your Go code:

   • Create a struct that represents the custom resource object.
   • Define methods for creating, updating, and deleting the resource.

3. Use the Kubernetes RESTClient to interact with the API:

   • Use the RESTClient().Post() method to create a new resource.
   • Specify the fully qualified path to the resource using AbsPath().
   • Marshal the resource object into JSON and set it as the request body.

Example Code for Creation:

<code class="go">kongPlugin := &KongPlugin{
    TypeMeta: metav1.TypeMeta{
        APIVersion: "configuration.konghq.com/v1",
        Kind:       "KongPlugin",
    },
    ObjectMeta: metav1.ObjectMeta{
        Name:      "add-response-header",
        Namespace: "default",
    },
    Config: KongPluginConfig{
        Add: KongPluginAdd{
            Headers: []string{"demo: injected-by-kong"},
        },
    },
    Plugin: "response-transformer",
}

body, err := json.Marshal(kongPlugin)
if err != nil {
    // Handle error
}

data, err := clientset.RESTClient().
    Post().
    AbsPath("/apis/configuration.konghq.com/v1/namespaces/default/kongplugins").
    Body(body).
    DoRaw(context.TODO())
if err != nil {
    // Handle error
}</code>

Retrieving a Custom Resource

To retrieve a custom resource, you need to:

1. Use the RESTClient().Get() method to make a request to the API.
2. Specify the fully qualified path to the resource using AbsPath().

Example Code for Retrieval:

<code class="go">data, err := clientset.RESTClient().
    Get().
    AbsPath("/apis/configuration.konghq.com/v1/namespaces/default/kongplugins/add-response-header").
    DoRaw(context.TODO())
if err != nil {
    // Handle error
}</code>

The data variable will contain the raw JSON response from the API, which you can parse to access the details of the custom resource.

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