discovery.go

package discovery

import (
	"fmt"
	"io/ioutil"
	"os"
	"strings"

	log "github.com/sirupsen/logrus"
	coreClient "k8s.io/client-go/kubernetes"
	restClient "k8s.io/client-go/rest"
	cmdClient "k8s.io/client-go/tools/clientcmd"
	metricsClient "k8s.io/metrics/pkg/client/clientset/versioned"
)

// K8s struct holds the instance of clientset and metrics clisentset
type K8s struct {
	Clientset        coreClient.Interface
	MetricsClientSet *metricsClient.Clientset
	RestConfig       *restClient.Config
}

var logEnabled bool

// NewK8s will provide a new k8s client interface
// resolves where it is running whether inside the kubernetes cluster or outside
// While running outside the cluster, tries to make use of the kubeconfig file
// While running inside the cluster resolved via pod environment uses the in-cluster config
func NewK8s() (*K8s, error) {
	client := K8s{}
	_, logEnabled = os.LookupEnv("CLIENTSET_LOG")

	config, err := restClient.InClusterConfig()
	if err != nil {
		kubeConfig :=
			cmdClient.NewDefaultClientConfigLoadingRules().GetDefaultFilename()
		config, err = cmdClient.BuildConfigFromFlags("", kubeConfig)
		if err != nil {
			return nil, err
		}
		if logEnabled {
			log.Info("Program running from outside of the cluster")
		}
	} else {
		if logEnabled {
			log.Info("Program running inside the cluster, picking the in-cluster configuration")
		}
	}
	client.Clientset, err = coreClient.NewForConfig(config)
	client.MetricsClientSet, err = metricsClient.NewForConfig(config)
	client.RestConfig = config

	return &client, nil
}

// GetVersion returns the version of the kubernetes cluster that is running
func (o *K8s) GetVersion() (string, error) {
	version, err := o.Clientset.Discovery().ServerVersion()
	if err != nil {
		return "", err
	}
	if logEnabled {
		log.Infof("Version of running k8s %v", version)
	}
	return fmt.Sprintf("%s", version), nil
}

// GetNamespace will return the current namespace for the running program
// Checks for the user passed ENV variable POD_NAMESPACE if not available
// pulls the namespace from pod, if not returns ""
func (o *K8s) GetNamespace() (string, error) {
	if ns := os.Getenv("POD_NAMESPACE"); ns != "" {
		return ns, nil
	}
	if data, err := ioutil.ReadFile("/var/run/secrets/kubernetes.io/serviceaccount/namespace"); err == nil {
		if ns := strings.TrimSpace(string(data)); len(ns) > 0 {
			return ns, nil
		}
		return "", err
	}
	return "", nil
}