Add fsnotify to monitor the configmap path

Signed-off-by: lubronzhan <lubronzhan@gmail.com>

cmd/contour/contour.go

@@ -18,6 +18,7 @@ import (
 
 	"github.com/alecthomas/kingpin/v2"
 	resource_v3 "github.com/envoyproxy/go-control-plane/pkg/resource/v3"
+	"github.com/fsnotify/fsnotify"
 	"github.com/sirupsen/logrus"
 	"go.uber.org/automaxprocs/maxprocs"
 
@@ -178,9 +179,20 @@ func main() {
 			log.WithError(err).Fatal("unable to initialize Server dependencies required to start Contour")
 		}
 
+		// Start a process to monitor the path of mounted configMap `/config`
+		// so that it can restart contour if the configMap gets updated.
+		watch, err := initializeWatch(defaultConfigPath, log)
+		if err != nil {
+			log.Fatalf("fail to initialize watch on configMap path '/config': %v\n", err)
+		}
+		defer func(watch *fsnotify.Watcher) {
+			_ = watch.Close() // ignore explicitly when the watch closes
+		}(watch)
+
 		if err := serve.doServe(); err != nil {
 			log.WithError(err).Fatal("Contour server failed")
 		}
+		return
 	case version.FullCommand():
 		println(build.PrintBuildInfo())
 	default:

cmd/contour/filewatcher.go

@@ -0,0 +1,50 @@
+// Copyright Project Contour Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"github.com/fsnotify/fsnotify"
+	"github.com/sirupsen/logrus"
+)
+
+const defaultConfigPath = "/config"
+
+// set up a filesystem watcher for the mounted files
+// right now just the configMap
+// reboot the app whenever there is an update via the returned stopCh.
+func initializeWatch(path string, log *logrus.Logger) (*fsnotify.Watcher, error) {
+	watch, err := fsnotify.NewWatcher()
+	if err != nil {
+		log.Fatalln("fail to setup config watcher")
+	}
+	go func() {
+		for {
+			select {
+			case err := <-watch.Errors:
+				log.Warningf("watcher receives err: %v\n", err)
+			case event := <-watch.Events:
+				if event.Op != fsnotify.Chmod {
+					log.Fatalf("restarting contour because received event %v on file %s\n", event.Op, defaultConfigPath)
+				} else {
+					log.Printf("watcher receives %s on the mounted file %s\n", event.Op.String(), event.Name)
+				}
+			}
+		}
+	}()
+
+	if err := watch.Add(path); err != nil {
+		log.Fatalf("fail to watch contour config file %s\n", path)
+	}
+	return watch, err
+}