agent: disable metrics server by default (#161)

agent/config/config.go

@@ -219,18 +219,34 @@ reconnect.`,
 }
 
 type ServerConfig struct {
+	// Enabled indicates whether to enable the agent metrics server.
+	Enabled bool `json:"enabled" yaml:"enabled"`
+
 	// BindAddr is the address to bind to listen for incoming HTTP connections.
 	BindAddr string `json:"bind_addr" yaml:"bind_addr"`
 }
 
 func (c *ServerConfig) Validate() error {
+	if !c.Enabled {
+		return nil
+	}
 	if c.BindAddr == "" {
 		return fmt.Errorf("missing bind addr")
 	}
 	return nil
 }
 
 func (c *ServerConfig) RegisterFlags(fs *pflag.FlagSet) {
+	fs.BoolVar(
+		&c.Enabled,
+		"server.enabled",
+		c.Enabled,
+		`
+Whether to enable the agent metrics server.
+
+Disabled by default.`,
+	)
+
 	fs.StringVar(
 		&c.BindAddr,
 		"server.bind-addr",

cli/agent/command.go

@@ -174,27 +174,29 @@ func runAgent(conf *config.Config, logger log.Logger) error {
 	}
 
 	// Agent server.
-	serverLn, err := net.Listen("tcp", conf.Server.BindAddr)
-	if err != nil {
-		return fmt.Errorf("server listen: %s: %w", conf.Server.BindAddr, err)
-	}
-	server := server.NewServer(registry, logger)
-
-	group.Add(func() error {
-		if err := server.Serve(serverLn); err != nil {
-			return fmt.Errorf("agent server: %w", err)
+	if conf.Server.Enabled {
+		serverLn, err := net.Listen("tcp", conf.Server.BindAddr)
+		if err != nil {
+			return fmt.Errorf("server listen: %s: %w", conf.Server.BindAddr, err)
 		}
-		return nil
-	}, func(error) {
-		shutdownCtx, cancel := context.WithTimeout(
-			context.Background(), conf.GracePeriod,
-		)
-		defer cancel()
+		server := server.NewServer(registry, logger)
 
-		if err := server.Shutdown(shutdownCtx); err != nil {
-			logger.Warn("failed to gracefully shutdown agent server", zap.Error(err))
-		}
-	})
+		group.Add(func() error {
+			if err := server.Serve(serverLn); err != nil {
+				return fmt.Errorf("agent server: %w", err)
+			}
+			return nil
+		}, func(error) {
+			shutdownCtx, cancel := context.WithTimeout(
+				context.Background(), conf.GracePeriod,
+			)
+			defer cancel()
+
+			if err := server.Shutdown(shutdownCtx); err != nil {
+				logger.Warn("failed to gracefully shutdown agent server", zap.Error(err))
+			}
+		})
+	}
 
 	// Termination handler.
 	signalCtx, signalCancel := context.WithCancel(context.Background())