feat: add ability for users to specify alternative kubeconfig and kubecontext

This will provide the possibility for users to talk to existing kubernetes clusters, thereby removing one of the biggest reasons for having the old scheduler-kubernetes plugin around.

plugins/scheduler-k3s/k8s.go

@@ -22,11 +22,22 @@ import (
 	"k8s.io/utils/ptr"
 )
 
+func getKubeconfigPath() string {
+	return common.PropertyGetDefault("scheduler-k3s", "--global", "kubeconfig-path", KubeConfigPath)
+}
+
+func getKubeContext() string {
+	return common.PropertyGetDefault("scheduler-k3s", "--global", "kube-context", DefaultKubeContext)
+}
+
 // KubernetesClient is a wrapper around the Kubernetes client
 type KubernetesClient struct {
 	// Client is the Kubernetes client
 	Client kubernetes.Clientset
 
+	// KubeConfigPath is the path to the Kubernetes config
+	KubeConfigPath string
+
 	// RestClient is the Kubernetes REST client
 	RestClient rest.Interface
 
@@ -36,7 +47,9 @@ type KubernetesClient struct {
 
 // NewKubernetesClient creates a new Kubernetes client
 func NewKubernetesClient() (KubernetesClient, error) {
-	clientConfig := KubernetesClientConfig()
+	kubeconfigPath := getKubeconfigPath()
+	kubeContext := getKubeContext()
+	clientConfig := KubernetesClientConfig(kubeconfigPath, kubeContext)
 	restConf, err := clientConfig.ClientConfig()
 	if err != nil {
 		return KubernetesClient{}, err
@@ -60,17 +73,29 @@ func NewKubernetesClient() (KubernetesClient, error) {
 	}
 
 	return KubernetesClient{
-		Client:     *client,
-		RestConfig: *restConf,
-		RestClient: restClient,
+		Client:         *client,
+		KubeConfigPath: kubeconfigPath,
+		RestConfig:     *restConf,
+		RestClient:     restClient,
 	}, nil
 }
 
 // KubernetesClientConfig returns a Kubernetes client config
-func KubernetesClientConfig() clientcmd.ClientConfig {
+func KubernetesClientConfig(kubeconfigPath string, kubecontext string) clientcmd.ClientConfig {
+	configOverrides := clientcmd.ConfigOverrides{ClusterInfo: clientcmdapi.Cluster{Server: ""}}
+	if kubecontext != "" {
+		configOverrides.CurrentContext = kubecontext
+	}
+
 	return clientcmd.NewNonInteractiveDeferredLoadingClientConfig(
-		&clientcmd.ClientConfigLoadingRules{ExplicitPath: KubeConfigPath},
-		&clientcmd.ConfigOverrides{ClusterInfo: clientcmdapi.Cluster{Server: ""}})
+		&clientcmd.ClientConfigLoadingRules{ExplicitPath: kubeconfigPath},
+		&configOverrides,
+	)
+}
+
+func (k KubernetesClient) Ping() error {
+	_, err := k.Client.Discovery().ServerVersion()
+	return err
 }
 
 // AnnotateNodeInput contains all the information needed to annotates a Kubernetes node
@@ -110,16 +135,23 @@ type ApplyKubernetesManifestInput struct {
 }
 
 func (k KubernetesClient) ApplyKubernetesManifest(ctx context.Context, input ApplyKubernetesManifestInput) error {
+	args := []string{
+		"apply",
+		"-f",
+		input.Manifest,
+	}
+
+	if kubeContext := getKubeContext(); kubeContext != "" {
+		args = append([]string{"--context", kubeContext}, args...)
+	}
+
+	if kubeconfigPath := getKubeconfigPath(); kubeconfigPath != "" {
+		args = append([]string{"--kubeconfig", kubeconfigPath}, args...)
+	}
+
 	upgradeCmd, err := common.CallExecCommand(common.ExecCommandInput{
-		Command: "kubectl",
-		Args: []string{
-			"apply",
-			"-f",
-			input.Manifest,
-		},
-		Env: map[string]string{
-			"KUBECONFIG": KubeConfigPath,
-		},
+		Command:     "kubectl",
+		Args:        args,
 		StreamStdio: true,
 	})
 	if err != nil {