feat(config): add "disabled" mutli cluster strategy (#360)

* feat: add 'disabled' ClusterProviderStrategy

Signed-off-by: Calum Murray <[email protected]>

* feat: add --disable-multi-cluster flag

Signed-off-by: Calum Murray <[email protected]>

* test: check that --disable-multi-cluster flag changes config

Signed-off-by: Calum Murray <[email protected]>

* refactor: move flag names to constants

Signed-off-by: Calum Murray <[email protected]>

* fix(test): correct subtest name

Signed-off-by: Calum Murray <[email protected]>

* fix: explicit clusterproviderstrategy is now recommended, instead of advisable

Signed-off-by: Calum Murray <[email protected]>

---------

Signed-off-by: Calum Murray <[email protected]>

Author: Cali0707

pkg/config/config.go

@@ -9,6 +9,7 @@ import (
 const (
 	ClusterProviderKubeConfig = "kubeconfig"
 	ClusterProviderInCluster  = "in-cluster"
+	ClusterProviderDisabled   = "disabled"
 )
 
 // StaticConfig is the configuration for the server.

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

@@ -47,9 +47,34 @@ kubernetes-mcp-server --port 8080
 
 # start a SSE server on port 8443 with a public HTTPS host of example.com
 kubernetes-mcp-server --port 8443 --sse-base-url https://example.com:8443
+
+# start a SSE server on port 8080 with multi-cluster tools disabled
+kubernetes-mcp-server --port 8080 --disable-multi-cluster
 `))
 )
 
+const (
+	flagVersion              = "version"
+	flagLogLevel             = "log-level"
+	flagConfig               = "config"
+	flagSSEPort              = "sse-port"
+	flagHttpPort             = "http-port"
+	flagPort                 = "port"
+	flagSSEBaseUrl           = "sse-base-url"
+	flagKubeconfig           = "kubeconfig"
+	flagToolsets             = "toolsets"
+	flagListOutput           = "list-output"
+	flagReadOnly             = "read-only"
+	flagDisableDestructive   = "disable-destructive"
+	flagRequireOAuth         = "require-oauth"
+	flagOAuthAudience        = "oauth-audience"
+	flagValidateToken        = "validate-token"
+	flagAuthorizationURL     = "authorization-url"
+	flagServerUrl            = "server-url"
+	flagCertificateAuthority = "certificate-authority"
+	flagDisableMultiCluster  = "disable-multi-cluster"
+)
+
 type MCPServerOptions struct {
 	Version              bool
 	LogLevel             int
@@ -68,6 +93,7 @@ type MCPServerOptions struct {
 	AuthorizationURL     string
 	CertificateAuthority string
 	ServerURL            string
+	DisableMultiCluster  bool
 
 	ConfigPath   string
 	StaticConfig *config.StaticConfig
@@ -104,32 +130,33 @@ func NewMCPServer(streams genericiooptions.IOStreams) *cobra.Command {
 		},
 	}
 
-	cmd.Flags().BoolVar(&o.Version, "version", o.Version, "Print version information and quit")
-	cmd.Flags().IntVar(&o.LogLevel, "log-level", o.LogLevel, "Set the log level (from 0 to 9)")
-	cmd.Flags().StringVar(&o.ConfigPath, "config", o.ConfigPath, "Path of the config file.")
-	cmd.Flags().IntVar(&o.SSEPort, "sse-port", o.SSEPort, "Start a SSE server on the specified port")
-	cmd.Flag("sse-port").Deprecated = "Use --port instead"
-	cmd.Flags().IntVar(&o.HttpPort, "http-port", o.HttpPort, "Start a streamable HTTP server on the specified port")
-	cmd.Flag("http-port").Deprecated = "Use --port instead"
-	cmd.Flags().StringVar(&o.Port, "port", o.Port, "Start a streamable HTTP and SSE HTTP server on the specified port (e.g. 8080)")
-	cmd.Flags().StringVar(&o.SSEBaseUrl, "sse-base-url", o.SSEBaseUrl, "SSE public base URL to use when sending the endpoint message (e.g. https://example.com)")
-	cmd.Flags().StringVar(&o.Kubeconfig, "kubeconfig", o.Kubeconfig, "Path to the kubeconfig file to use for authentication")
-	cmd.Flags().StringSliceVar(&o.Toolsets, "toolsets", o.Toolsets, "Comma-separated list of MCP toolsets to use (available toolsets: "+strings.Join(toolsets.ToolsetNames(), ", ")+"). Defaults to "+strings.Join(o.StaticConfig.Toolsets, ", ")+".")
-	cmd.Flags().StringVar(&o.ListOutput, "list-output", o.ListOutput, "Output format for resource list operations (one of: "+strings.Join(output.Names, ", ")+"). Defaults to "+o.StaticConfig.ListOutput+".")
-	cmd.Flags().BoolVar(&o.ReadOnly, "read-only", o.ReadOnly, "If true, only tools annotated with readOnlyHint=true are exposed")
-	cmd.Flags().BoolVar(&o.DisableDestructive, "disable-destructive", o.DisableDestructive, "If true, tools annotated with destructiveHint=true are disabled")
-	cmd.Flags().BoolVar(&o.RequireOAuth, "require-oauth", o.RequireOAuth, "If true, requires OAuth authorization as defined in the Model Context Protocol (MCP) specification. This flag is ignored if transport type is stdio")
-	_ = cmd.Flags().MarkHidden("require-oauth")
-	cmd.Flags().StringVar(&o.OAuthAudience, "oauth-audience", o.OAuthAudience, "OAuth audience for token claims validation. Optional. If not set, the audience is not validated. Only valid if require-oauth is enabled.")
-	_ = cmd.Flags().MarkHidden("oauth-audience")
-	cmd.Flags().BoolVar(&o.ValidateToken, "validate-token", o.ValidateToken, "If true, validates the token against the Kubernetes API Server using TokenReview. Optional. If not set, the token is not validated. Only valid if require-oauth is enabled.")
-	_ = cmd.Flags().MarkHidden("validate-token")
-	cmd.Flags().StringVar(&o.AuthorizationURL, "authorization-url", o.AuthorizationURL, "OAuth authorization server URL for protected resource endpoint. If not provided, the Kubernetes API server host will be used. Only valid if require-oauth is enabled.")
-	_ = cmd.Flags().MarkHidden("authorization-url")
-	cmd.Flags().StringVar(&o.ServerURL, "server-url", o.ServerURL, "Server URL of this application. Optional. If set, this url will be served in protected resource metadata endpoint and tokens will be validated with this audience. If not set, expected audience is kubernetes-mcp-server. Only valid if require-oauth is enabled.")
-	_ = cmd.Flags().MarkHidden("server-url")
-	cmd.Flags().StringVar(&o.CertificateAuthority, "certificate-authority", o.CertificateAuthority, "Certificate authority path to verify certificates. Optional. Only valid if require-oauth is enabled.")
-	_ = cmd.Flags().MarkHidden("certificate-authority")
+	cmd.Flags().BoolVar(&o.Version, flagVersion, o.Version, "Print version information and quit")
+	cmd.Flags().IntVar(&o.LogLevel, flagLogLevel, o.LogLevel, "Set the log level (from 0 to 9)")
+	cmd.Flags().StringVar(&o.ConfigPath, flagConfig, o.ConfigPath, "Path of the config file.")
+	cmd.Flags().IntVar(&o.SSEPort, flagSSEPort, o.SSEPort, "Start a SSE server on the specified port")
+	cmd.Flag(flagSSEPort).Deprecated = "Use --port instead"
+	cmd.Flags().IntVar(&o.HttpPort, flagHttpPort, o.HttpPort, "Start a streamable HTTP server on the specified port")
+	cmd.Flag(flagHttpPort).Deprecated = "Use --port instead"
+	cmd.Flags().StringVar(&o.Port, flagPort, o.Port, "Start a streamable HTTP and SSE HTTP server on the specified port (e.g. 8080)")
+	cmd.Flags().StringVar(&o.SSEBaseUrl, flagSSEBaseUrl, o.SSEBaseUrl, "SSE public base URL to use when sending the endpoint message (e.g. https://example.com)")
+	cmd.Flags().StringVar(&o.Kubeconfig, flagKubeconfig, o.Kubeconfig, "Path to the kubeconfig file to use for authentication")
+	cmd.Flags().StringSliceVar(&o.Toolsets, flagToolsets, o.Toolsets, "Comma-separated list of MCP toolsets to use (available toolsets: "+strings.Join(toolsets.ToolsetNames(), ", ")+"). Defaults to "+strings.Join(o.StaticConfig.Toolsets, ", ")+".")
+	cmd.Flags().StringVar(&o.ListOutput, flagListOutput, o.ListOutput, "Output format for resource list operations (one of: "+strings.Join(output.Names, ", ")+"). Defaults to "+o.StaticConfig.ListOutput+".")
+	cmd.Flags().BoolVar(&o.ReadOnly, flagReadOnly, o.ReadOnly, "If true, only tools annotated with readOnlyHint=true are exposed")
+	cmd.Flags().BoolVar(&o.DisableDestructive, flagDisableDestructive, o.DisableDestructive, "If true, tools annotated with destructiveHint=true are disabled")
+	cmd.Flags().BoolVar(&o.RequireOAuth, flagRequireOAuth, o.RequireOAuth, "If true, requires OAuth authorization as defined in the Model Context Protocol (MCP) specification. This flag is ignored if transport type is stdio")
+	_ = cmd.Flags().MarkHidden(flagRequireOAuth)
+	cmd.Flags().StringVar(&o.OAuthAudience, flagOAuthAudience, o.OAuthAudience, "OAuth audience for token claims validation. Optional. If not set, the audience is not validated. Only valid if require-oauth is enabled.")
+	_ = cmd.Flags().MarkHidden(flagOAuthAudience)
+	cmd.Flags().BoolVar(&o.ValidateToken, flagValidateToken, o.ValidateToken, "If true, validates the token against the Kubernetes API Server using TokenReview. Optional. If not set, the token is not validated. Only valid if require-oauth is enabled.")
+	_ = cmd.Flags().MarkHidden(flagValidateToken)
+	cmd.Flags().StringVar(&o.AuthorizationURL, flagAuthorizationURL, o.AuthorizationURL, "OAuth authorization server URL for protected resource endpoint. If not provided, the Kubernetes API server host will be used. Only valid if require-oauth is enabled.")
+	_ = cmd.Flags().MarkHidden(flagAuthorizationURL)
+	cmd.Flags().StringVar(&o.ServerURL, flagServerUrl, o.ServerURL, "Server URL of this application. Optional. If set, this url will be served in protected resource metadata endpoint and tokens will be validated with this audience. If not set, expected audience is kubernetes-mcp-server. Only valid if require-oauth is enabled.")
+	_ = cmd.Flags().MarkHidden(flagServerUrl)
+	cmd.Flags().StringVar(&o.CertificateAuthority, flagCertificateAuthority, o.CertificateAuthority, "Certificate authority path to verify certificates. Optional. Only valid if require-oauth is enabled.")
+	_ = cmd.Flags().MarkHidden(flagCertificateAuthority)
+	cmd.Flags().BoolVar(&o.DisableMultiCluster, flagDisableMultiCluster, o.DisableMultiCluster, "Disable multi cluster tools. Optional. If true, all tools will be run against the default cluster/context.")
 
 	return cmd
 }
@@ -156,52 +183,55 @@ func (m *MCPServerOptions) Complete(cmd *cobra.Command) error {
 }
 
 func (m *MCPServerOptions) loadFlags(cmd *cobra.Command) {
-	if cmd.Flag("log-level").Changed {
+	if cmd.Flag(flagLogLevel).Changed {
 		m.StaticConfig.LogLevel = m.LogLevel
 	}
-	if cmd.Flag("port").Changed {
+	if cmd.Flag(flagPort).Changed {
 		m.StaticConfig.Port = m.Port
-	} else if cmd.Flag("sse-port").Changed {
+	} else if cmd.Flag(flagSSEPort).Changed {
 		m.StaticConfig.Port = strconv.Itoa(m.SSEPort)
-	} else if cmd.Flag("http-port").Changed {
+	} else if cmd.Flag(flagHttpPort).Changed {
 		m.StaticConfig.Port = strconv.Itoa(m.HttpPort)
 	}
-	if cmd.Flag("sse-base-url").Changed {
+	if cmd.Flag(flagSSEBaseUrl).Changed {
 		m.StaticConfig.SSEBaseURL = m.SSEBaseUrl
 	}
-	if cmd.Flag("kubeconfig").Changed {
+	if cmd.Flag(flagKubeconfig).Changed {
 		m.StaticConfig.KubeConfig = m.Kubeconfig
 	}
-	if cmd.Flag("list-output").Changed {
+	if cmd.Flag(flagListOutput).Changed {
 		m.StaticConfig.ListOutput = m.ListOutput
 	}
-	if cmd.Flag("read-only").Changed {
+	if cmd.Flag(flagReadOnly).Changed {
 		m.StaticConfig.ReadOnly = m.ReadOnly
 	}
-	if cmd.Flag("disable-destructive").Changed {
+	if cmd.Flag(flagDisableDestructive).Changed {
 		m.StaticConfig.DisableDestructive = m.DisableDestructive
 	}
-	if cmd.Flag("toolsets").Changed {
+	if cmd.Flag(flagToolsets).Changed {
 		m.StaticConfig.Toolsets = m.Toolsets
 	}
-	if cmd.Flag("require-oauth").Changed {
+	if cmd.Flag(flagRequireOAuth).Changed {
 		m.StaticConfig.RequireOAuth = m.RequireOAuth
 	}
-	if cmd.Flag("oauth-audience").Changed {
+	if cmd.Flag(flagOAuthAudience).Changed {
 		m.StaticConfig.OAuthAudience = m.OAuthAudience
 	}
-	if cmd.Flag("validate-token").Changed {
+	if cmd.Flag(flagValidateToken).Changed {
 		m.StaticConfig.ValidateToken = m.ValidateToken
 	}
-	if cmd.Flag("authorization-url").Changed {
+	if cmd.Flag(flagAuthorizationURL).Changed {
 		m.StaticConfig.AuthorizationURL = m.AuthorizationURL
 	}
-	if cmd.Flag("server-url").Changed {
+	if cmd.Flag(flagServerUrl).Changed {
 		m.StaticConfig.ServerURL = m.ServerURL
 	}
-	if cmd.Flag("certificate-authority").Changed {
+	if cmd.Flag(flagCertificateAuthority).Changed {
 		m.StaticConfig.CertificateAuthority = m.CertificateAuthority
 	}
+	if cmd.Flag(flagDisableMultiCluster).Changed && m.DisableMultiCluster {
+		m.StaticConfig.ClusterProviderStrategy = config.ClusterProviderDisabled
+	}
 }
 
 func (m *MCPServerOptions) initializeLogging() {
@@ -258,6 +288,13 @@ func (m *MCPServerOptions) Run() error {
 	klog.V(1).Infof(" - Read-only mode: %t", m.StaticConfig.ReadOnly)
 	klog.V(1).Infof(" - Disable destructive tools: %t", m.StaticConfig.DisableDestructive)
 
+	strategy := m.StaticConfig.ClusterProviderStrategy
+	if strategy == "" {
+		strategy = "auto-detect (it is recommended to set this explicitly in your Config)"
+	}
+
+	klog.V(1).Infof(" - ClusterProviderStrategy: %s", strategy)
+
 	if m.Version {
 		_, _ = fmt.Fprintf(m.Out, "%s\n", version.Version)
 		return nil

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

@@ -276,3 +276,24 @@ func TestStdioLogging(t *testing.T) {
 		assert.Containsf(t, out.String(), "Starting kubernetes-mcp-server", "Expected klog output, got %s", out.String())
 	})
 }
+
+func TestDisableMultiCluster(t *testing.T) {
+	t.Run("defaults to false", func(t *testing.T) {
+		ioStreams, out := testStream()
+		rootCmd := NewMCPServer(ioStreams)
+		rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1"})
+		if err := rootCmd.Execute(); !strings.Contains(out.String(), " - ClusterProviderStrategy: auto-detect (it is recommended to set this explicitly in your Config)") {
+			t.Fatalf("Expected ClusterProviderStrategy kubeconfig, got %s %v", out, err)
+		}
+	})
+	t.Run("set with --disable-multi-cluster", func(t *testing.T) {
+		ioStreams, out := testStream()
+		rootCmd := NewMCPServer(ioStreams)
+		rootCmd.SetArgs([]string{"--version", "--port=1337", "--log-level=1", "--disable-multi-cluster"})
+		_ = rootCmd.Execute()
+		expected := `(?m)\" - ClusterProviderStrategy\: disabled\"`
+		if m, err := regexp.MatchString(expected, out.String()); !m || err != nil {
+			t.Fatalf("Expected ClusterProviderStrategy %s, got %s %v", expected, out.String(), err)
+		}
+	})
+}

pkg/kubernetes/provider.go

@@ -32,25 +32,30 @@ type kubeConfigClusterProvider struct {
 
 var _ ManagerProvider = &kubeConfigClusterProvider{}
 
-type inClusterProvider struct {
-	manager *Manager
+type singleClusterProvider struct {
+	strategy string
+	manager  *Manager
 }
 
-var _ ManagerProvider = &inClusterProvider{}
+var _ ManagerProvider = &singleClusterProvider{}
 
 func NewManagerProvider(cfg *config.StaticConfig) (ManagerProvider, error) {
 	m, err := NewManager(cfg)
 	if err != nil {
 		return nil, err
 	}
 
-	switch resolveStrategy(cfg, m) {
+	strategy := resolveStrategy(cfg, m)
+	switch strategy {
 	case config.ClusterProviderKubeConfig:
 		return newKubeConfigClusterProvider(m)
-	case config.ClusterProviderInCluster:
-		return newInClusterProvider(m)
+	case config.ClusterProviderInCluster, config.ClusterProviderDisabled:
+		return newSingleClusterProvider(m, strategy)
 	default:
-		return nil, fmt.Errorf("invalid ClusterProviderStrategy '%s', must be 'kubeconfig' or 'in-cluster'", cfg.ClusterProviderStrategy)
+		return nil, fmt.Errorf(
+			"invalid ClusterProviderStrategy '%s', must be 'kubeconfig', 'in-cluster', or 'disabled'",
+			strategy,
+		)
 	}
 }
 
@@ -83,9 +88,14 @@ func newKubeConfigClusterProvider(m *Manager) (*kubeConfigClusterProvider, error
 	}, nil
 }
 
-func newInClusterProvider(m *Manager) (*inClusterProvider, error) {
-	return &inClusterProvider{
-		manager: m,
+func newSingleClusterProvider(m *Manager, strategy string) (*singleClusterProvider, error) {
+	if strategy == config.ClusterProviderInCluster && !m.IsInCluster() {
+		return nil, fmt.Errorf("server must be deployed in cluster for the in-cluster ClusterProviderStrategy")
+	}
+
+	return &singleClusterProvider{
+		manager:  m,
+		strategy: strategy,
 	}, nil
 }
 
@@ -141,32 +151,32 @@ func (k *kubeConfigClusterProvider) Close() {
 	m.Close()
 }
 
-func (i *inClusterProvider) GetTargets(ctx context.Context) ([]string, error) {
+func (s *singleClusterProvider) GetTargets(ctx context.Context) ([]string, error) {
 	return []string{""}, nil
 }
 
-func (i *inClusterProvider) GetManagerFor(ctx context.Context, target string) (*Manager, error) {
+func (s *singleClusterProvider) GetManagerFor(ctx context.Context, target string) (*Manager, error) {
 	if target != "" {
-		return nil, fmt.Errorf("unable to get manager for other context/cluster with in-cluster strategy")
+		return nil, fmt.Errorf("unable to get manager for other context/cluster with %s strategy", s.strategy)
 	}
 
-	return i.manager, nil
+	return s.manager, nil
 }
 
-func (i *inClusterProvider) GetDefaultTarget() string {
+func (s *singleClusterProvider) GetDefaultTarget() string {
 	return ""
 }
 
-func (i *inClusterProvider) GetTargetParameterName() string {
+func (s *singleClusterProvider) GetTargetParameterName() string {
 	return ""
 }
 
-func (i *inClusterProvider) WatchTargets(watch func() error) {
-	i.manager.WatchKubeConfig(watch)
+func (s *singleClusterProvider) WatchTargets(watch func() error) {
+	s.manager.WatchKubeConfig(watch)
 }
 
-func (i *inClusterProvider) Close() {
-	i.manager.Close()
+func (s *singleClusterProvider) Close() {
+	s.manager.Close()
 }
 
 func (m *Manager) newForContext(context string) (*Manager, error) {