Simple K8s client to query API resources

go.mod

module simple-k8s-client

go 1.15

require (
	github.com/golang/protobuf v1.4.2 // indirect
	github.com/imdario/mergo v0.3.11 // indirect
	golang.org/x/crypto v0.0.0-20200728195943-123391ffb6de // indirect
	golang.org/x/net v0.0.0-20200813134508-3edf25e44fcc // indirect
	golang.org/x/oauth2 v0.0.0-20200107190931-bf48bf16ab8d // indirect
	golang.org/x/time v0.0.0-20200630173020-3af7569d3a1e // indirect
	k8s.io/client-go v0.18.8
	k8s.io/utils v0.0.0-20200815180417-3bc9d57fc792 // indirect
)

main.go

package main

import (
	"flag"
	"fmt"
	"log"
	"strings"

	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/tools/clientcmd"
)

func main() {

	// flag.String() returns a _pointer_ to a string ('*string' vs 'string').
	// This means we have to access it using '*' if we need a string value instead of a string pointer, for example '*kubeAPIAddress'.
	var kubeAPIAddress, kubeConfPath *string

	kubeAPIAddress = flag.String("kubeAPI", "", "Kuberenetes API address. Leave empty to auto-discover.")
	kubeConfPath = flag.String("kubeConf", "", "Kube config path. Leave empty to auto-discover.")

	// We have to parse the commandline flags before we can use them.
	flag.Parse()

	// Build a Rest config. Passing the values with '*' since BuildConfigFromFlags wants string values, not string pointers.
	restConfig, err := clientcmd.BuildConfigFromFlags(*kubeAPIAddress, *kubeConfPath)
	if err != nil {
		log.Fatalf("failed to build k8s rest config, %s\n", err.Error())
	}

	// Using the rest config, get a K8s clientSet. The client set can be used to
	// return all different clients we might need to query different apis.
	// For example, ClientSet.AppsV1() to get a Apps/v1 client for querying
	// Deployments.
	ClientSet, err := kubernetes.NewForConfig(restConfig)
	if err != nil {
		log.Fatalf("failed to create k8s clientset from rest config, %s\n", err.Error())
	}

	// Get a Server Groups and Resources client to list all the available
	// resources and API groups. It's quite a few of them so need to be a
	// bit selective probably.
	apiGroups, apiResources, err := ClientSet.ServerGroupsAndResources()
	if err != nil {
		log.Fatalf("failed to retreive api groups and resources, %s\n", err.Error())
	}

	// Let's print out the API groups and resources we find in a somewhat
	// easy to read tab format.

	fmt.Println("API Groups:")

	// Print all the API groups we find
	for _, apiGroup := range apiGroups {
		fmt.Printf("\tName: %s\n", apiGroup.Name)
	}

	fmt.Printf("\nAPI Resources:\n")

	// Print all the api resource lists we find.
	for _, apiResourceList := range apiResources {

		// Custom metrics is extremely noisy, skip it.
		if apiResourceList.GroupVersion == "custom.metrics.k8s.io/v1beta1" {
			continue
		}
		fmt.Printf("Group Version: %s\n", apiResourceList.GroupVersion)

		// For each api resource list, print the api resources in that list.
		for _, apiResource := range apiResourceList.APIResources {
			fmt.Printf("\tName: %s\n", apiResource.Name)
			fmt.Printf("\tKind: %s\n", apiResource.Kind)
			fmt.Printf("\tNamespaced: %v\n", apiResource.Namespaced)

			// Join the available verbs and print them newline separated
			sepVerbs := strings.Join(apiResource.Verbs, "\n\t\t")
			fmt.Printf("\tVerbs:\n\t\t%s\n\n", sepVerbs)
		}
	}
}