K8s pod density check

go.mod

module podchecker

go 1.16

require (
	github.com/olekukonko/tablewriter v0.0.5 // indirect
	k8s.io/api v0.22.4 // indirect
	k8s.io/apimachinery v0.22.4 // indirect
	k8s.io/client-go v0.22.4 // indirect
)

main.go

package main

import (
	"context"
	"flag"
	"fmt"
	"github.com/olekukonko/tablewriter"
	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
	"k8s.io/client-go/kubernetes"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/clientcmd"
	"k8s.io/client-go/util/homedir"
	"os"
	"path/filepath"
)

func main() {
	var kubeconfig *string
	if home := homedir.HomeDir(); home != "" {
		kubeconfig = flag.String("kubeconfig", filepath.Join(home, ".kube", "config"), "(optional) absolute path to the kubeconfig file")
	} else {
		kubeconfig = flag.String("kubeconfig", "", "absolute path to the kubeconfig file")
	}
	flag.Parse()

	config, err := buildConfigFromFlags("development", *kubeconfig)
	if err != nil {
		panic(err.Error())
	}

	clientset, err := kubernetes.NewForConfig(config)
	if err != nil {
		panic(err.Error())
	}

	table := tablewriter.NewWriter(os.Stdout)
	table.SetHeader([]string{"Node", "AZ", "Capacity", "Used"})

	nodes, err := clientset.CoreV1().Nodes().List(context.TODO(), metav1.ListOptions{})
	for _, node := range nodes.Items {
		podCapacity := node.Status.Capacity.Pods().Value()
		az := node.Labels["topology.kubernetes.io/zone"]
		nodeName := node.Name
		pods, _ := clientset.CoreV1().Pods("").List(context.TODO(), metav1.ListOptions{
			FieldSelector: "spec.nodeName=" + nodeName,
		})
		podsOnNode := len(pods.Items)

		table.Append([]string{nodeName, az, fmt.Sprintf("%d", podCapacity), fmt.Sprintf("%d", podsOnNode)})
	}

	table.Render()
}

func buildConfigFromFlags(context, kubeconfigPath string) (*rest.Config, error) {
	return clientcmd.NewNonInteractiveDeferredLoadingClientConfig(
		&clientcmd.ClientConfigLoadingRules{ExplicitPath: kubeconfigPath},
		&clientcmd.ConfigOverrides{
			CurrentContext: context,
		}).ClientConfig()
}