discovery_dynamic_client.go

discovery_dynamic_client.go

package main

import (
	"context"
	"fmt"
	"os"
	"path/filepath"

	"k8s.io/klog/v2"

	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/apimachinery/pkg/runtime/schema"
	"k8s.io/client-go/discovery"
	cacheddiscovery "k8s.io/client-go/discovery/cached/memory"
	"k8s.io/client-go/dynamic"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/restmapper"
	"k8s.io/client-go/tools/clientcmd"
)

func main() {
	// Enable trace logging of requests / responses to see config loading, discovery requests, and the API request
	var level klog.Level
	if err := level.Set("8"); err != nil {
		checkErr(err)
	}

	clientConfig, err := getClientConfig()
	checkErr(err)

	dynamicClient, err := dynamic.NewForConfig(clientConfig)
	checkErr(err)

	discoveryClient, err := discovery.NewDiscoveryClientForConfig(clientConfig)
	checkErr(err)

	// use discovery information to find what versions the server has available
	discoveryRESTMapper := restmapper.NewDeferredDiscoveryRESTMapper(cacheddiscovery.NewMemCacheClient(discoveryClient))
	desiredGroupResource := schema.GroupVersionResource{Group: "apps", Resource: "deployments"}
	availableGroupResourceVersions, err := discoveryRESTMapper.ResourcesFor(desiredGroupResource)
	checkErr(err)

	if len(availableGroupResourceVersions) == 0 {
		fmt.Printf("no versions of %v available\n", desiredGroupResource)
	} else {
		fmt.Printf("resolved %v to %v\n", desiredGroupResource, availableGroupResourceVersions[0])
		items, err := dynamicClient.Resource(availableGroupResourceVersions[0]).List(context.TODO(), metav1.ListOptions{})
		checkErr(err)
		fmt.Printf("found %d items for %v\n", len(items.Items), availableGroupResourceVersions[0])
	}
}

func getClientConfig() (*rest.Config, error) {
	// build client config from $KUBECONFIG or default location
	kubeconfigPath := os.Getenv("KUBECONFIG")
	if kubeconfigPath == "" {
		homeDir, err := os.UserHomeDir()
		if err != nil {
			panic(err)
		}
		kubeconfigPath = filepath.Join(homeDir, ".kube", "kubeconfig")
	}
	return clientcmd.BuildConfigFromFlags("", kubeconfigPath)
}

func checkErr(err error) {
	if err != nil {
		fmt.Println(err)
		os.Exit(1)
	}
}