feat: watch for configuration changes

Watch kube config files for changes.
Automatically reload kubernetes client and list of tools.

Useful for logins or context changes after an MCP session has started.

pkg/kubernetes-mcp-server/cmd/root.go

@@ -42,6 +42,7 @@ Kubernetes Model Context Protocol (MCP) server
 		if err != nil {
 			panic(err)
 		}
+		defer mcpServer.Close()
 
 		var sseServer *server.SSEServer
 		if ssePort := viper.GetInt("sse-port"); ssePort > 0 {
@@ -49,13 +50,11 @@ Kubernetes Model Context Protocol (MCP) server
 			if err := sseServer.Start(fmt.Sprintf(":%d", ssePort)); err != nil {
 				panic(err)
 			}
+			defer sseServer.Shutdown(cmd.Context())
 		}
 		if err := mcpServer.ServeStdio(); err != nil && !errors.Is(err, context.Canceled) {
 			panic(err)
 		}
-		if sseServer != nil {
-			_ = sseServer.Shutdown(cmd.Context())
-		}
 	},
 }
 

pkg/kubernetes/kubernetes.go

@@ -1,6 +1,7 @@
 package kubernetes
 
 import (
+	"github.com/fsnotify/fsnotify"
 	"k8s.io/apimachinery/pkg/apis/meta/v1/unstructured"
 	"k8s.io/client-go/discovery"
 	"k8s.io/client-go/discovery/cached/memory"
@@ -17,8 +18,12 @@ import (
 // Exposed for testing
 var InClusterConfig = rest.InClusterConfig
 
+type CloseWatchKubeConfig func() error
+
 type Kubernetes struct {
 	cfg                         *rest.Config
+	kubeConfigFiles             []string
+	CloseWatchKubeConfig        CloseWatchKubeConfig
 	clientSet                   *kubernetes.Clientset
 	discoveryClient             *discovery.DiscoveryClient
 	deferredDiscoveryRESTMapper *restmapper.DeferredDiscoveryRESTMapper
@@ -44,6 +49,7 @@ func NewKubernetes() (*Kubernetes, error) {
 	}
 	return &Kubernetes{
 		cfg:                         cfg,
+		kubeConfigFiles:             resolveConfig().ConfigAccess().GetLoadingPrecedence(),
 		clientSet:                   clientSet,
 		discoveryClient:             discoveryClient,
 		deferredDiscoveryRESTMapper: restmapper.NewDeferredDiscoveryRESTMapper(memory.NewMemCacheClient(discoveryClient)),
@@ -51,6 +57,44 @@ func NewKubernetes() (*Kubernetes, error) {
 	}, nil
 }
 
+func (k *Kubernetes) WatchKubeConfig(onKubeConfigChange func() error) {
+	if len(k.kubeConfigFiles) == 0 {
+		return
+	}
+	watcher, err := fsnotify.NewWatcher()
+	if err != nil {
+		return
+	}
+	for _, file := range k.kubeConfigFiles {
+		_ = watcher.Add(file)
+	}
+	go func() {
+		for {
+			select {
+			case _, ok := <-watcher.Events:
+				if !ok {
+					return
+				}
+				_ = onKubeConfigChange()
+			case _, ok := <-watcher.Errors:
+				if !ok {
+					return
+				}
+			}
+		}
+	}()
+	if k.CloseWatchKubeConfig != nil {
+		_ = k.CloseWatchKubeConfig()
+	}
+	k.CloseWatchKubeConfig = watcher.Close
+}
+
+func (k *Kubernetes) Close() {
+	if k.CloseWatchKubeConfig != nil {
+		_ = k.CloseWatchKubeConfig()
+	}
+}
+
 func marshal(v any) (string, error) {
 	switch t := v.(type) {
 	case []unstructured.Unstructured:

pkg/mcp/common_test.go

@@ -129,6 +129,7 @@ func (c *mcpContext) beforeEach(t *testing.T) {
 
 func (c *mcpContext) afterEach() {
 	c.cancel()
+	c.mcpServer.Close()
 	_ = c.mcpClient.Close()
 	c.mcpHttpServer.Close()
 }

pkg/mcp/mcp.go

@@ -27,6 +27,7 @@ func NewSever() (*Server, error) {
 	if err := s.reloadKubernetesClient(); err != nil {
 		return nil, err
 	}
+	s.k.WatchKubeConfig(s.reloadKubernetesClient)
 	return s, nil
 }
 
@@ -57,6 +58,12 @@ func (s *Server) ServeSse(baseUrl string) *server.SSEServer {
 	return server.NewSSEServer(s.server, options...)
 }
 
+func (s *Server) Close() {
+	if s.k != nil {
+		s.k.Close()
+	}
+}
+
 func NewTextResult(content string, err error) *mcp.CallToolResult {
 	if err != nil {
 		return &mcp.CallToolResult{

pkg/mcp/mcp_test.go

@@ -1,12 +1,51 @@
 package mcp
 
 import (
+	"context"
 	"github.com/mark3labs/mcp-go/mcp"
+	"os"
+	"path/filepath"
 	"slices"
 	"strings"
 	"testing"
+	"time"
 )
 
+func TestWatchKubeConfig(t *testing.T) {
+	testCase(t, func(c *mcpContext) {
+		// Given
+		withTimeout, cancel := context.WithTimeout(c.ctx, 5*time.Second)
+		defer cancel()
+		var notification *mcp.JSONRPCNotification
+		c.mcpClient.OnNotification(func(n mcp.JSONRPCNotification) {
+			notification = &n
+		})
+		// When
+		f, _ := os.OpenFile(filepath.Join(c.tempDir, "config"), os.O_APPEND|os.O_WRONLY, 0644)
+		_, _ = f.WriteString("\n")
+		for {
+			if notification != nil {
+				break
+			}
+			select {
+			case <-withTimeout.Done():
+				break
+			default:
+				time.Sleep(100 * time.Millisecond)
+			}
+		}
+		// Then
+		t.Run("WatchKubeConfig notifies tools change", func(t *testing.T) {
+			if notification == nil {
+				t.Fatalf("WatchKubeConfig did not notify")
+			}
+			if notification.Method != "notifications/tools/list_changed" {
+				t.Fatalf("WatchKubeConfig did not notify tools change, got %s", notification.Method)
+			}
+		})
+	})
+}
+
 func TestTools(t *testing.T) {
 	expectedNames := []string{
 		"configuration_view",