How do you create and retrieve custom Kubernetes resources like KongPlugins in Go?

Creating and Retrieving Custom Kubernetes Resources

Introduction

Managing custom Kubernetes resources in code requires understanding the specific mechanisms for creation and retrieval. This article demonstrates how to create and get custom resources for Kong in Go, addressing common challenges faced when working with non-standard resource types.

Creating a Custom Resource

To create a custom resource, such as a KongPlugin, the following code can be used:

<code class="go">body, err := json.Marshal(&KongPlugin{
    TypeMeta: metav1.TypeMeta{
        APIVersion: "configuration.konghq.com/v1",
        Kind:       "KongPlugin",
    },
    ObjectMeta: metav1.ObjectMeta{
        Name:      "add-response-header",
        Namespace: "<namespace>",
    },
    Config: KongPluginConfig{
        Add: KongPluginConfigAdd{
            Headers: []string{"demo: injected-by-kong"},
        },
    },
    Plugin: "response-transformer",
})

data, err := clientset.RESTClient().
    Post().
    AbsPath("/apis/configuration.konghq.com/v1/namespaces/<namespace>/kongplugins").
    Body(body).
    DoRaw(context.TODO())</code>

Here, the KongPlugin data is marshalled and sent as the body of the request. The AbsPath function provides the path to the custom resource's API endpoint.

Retrieving a Custom Resource

To retrieve a custom resource, the following code can be used:

<code class="go">data, err := clientset.RESTClient().
    Get().
    AbsPath("/apis/configuration.konghq.com/v1/namespaces/<namespace>/kongplugins/kongplugin-sample").
    DoRaw(context.TODO())</code>

The AbsPath function again provides the path to the custom resource's API endpoint. The returned data contains the raw data of the resource.

Troubleshooting Errors

If the retrieval fails with an error such as "the server could not find the requested resource (get KongPlugin)", ensure that the following steps are taken:

• The custom resource definition (CRD) is installed correctly.
• The serviceaccount used by the application has the necessary permissions to view the resource.
• The request is made with the correct namespace and resource name.

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