Reopen log files after receiving a SIGHUP signal (#13112)

* Reopen log files after receiving a SIGHUP signal

Implements a system signals listener in log.FileLogWriter.

After receiving a SIGHUP signal from the system, the listener will close the current log file and then open it again.

The listener will finishes after receiving a SIGINT, SIGKILL or SIGTERM signal.

Closes grafana/grafana#2497

* Move the SIGHUP handling to the main file

pkg/cmd/grafana-server/main.go

@@ -96,13 +96,17 @@ func main() {
 
 func listenToSystemSignals(server *GrafanaServerImpl) {
 	signalChan := make(chan os.Signal, 1)
-	ignoreChan := make(chan os.Signal, 1)
+	sighupChan := make(chan os.Signal, 1)
 
-	signal.Notify(ignoreChan, syscall.SIGHUP)
+	signal.Notify(sighupChan, syscall.SIGHUP)
 	signal.Notify(signalChan, os.Interrupt, os.Kill, syscall.SIGTERM)
 
+	for {
 		select {
+		case _ = <-sighupChan:
+			log.Reload()
 		case sig := <-signalChan:
 			server.Shutdown(fmt.Sprintf("System signal: %s", sig))
 		}
+	}
 }

pkg/log/file.go

@@ -236,3 +236,20 @@ func (w *FileLogWriter) Close() {
 func (w *FileLogWriter) Flush() {
 	w.mw.fd.Sync()
 }
+
+// Reload file logger
+func (w *FileLogWriter) Reload() {
+	// block Logger's io.Writer
+	w.mw.Lock()
+	defer w.mw.Unlock()
+
+	// Close
+	fd := w.mw.fd
+	fd.Close()
+
+	// Open again
+	err := w.StartLogger()
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Reload StartLogger: %s\n", err)
+	}
+}

pkg/log/handlers.go

@@ -3,3 +3,7 @@ package log
 type DisposableHandler interface {
 	Close()
 }
+
+type ReloadableHandler interface {
+	Reload()
+}

pkg/log/log.go

@@ -21,10 +21,12 @@ import (
 
 var Root log15.Logger
 var loggersToClose []DisposableHandler
+var loggersToReload []ReloadableHandler
 var filters map[string]log15.Lvl
 
 func init() {
 	loggersToClose = make([]DisposableHandler, 0)
+	loggersToReload = make([]ReloadableHandler, 0)
 	Root = log15.Root()
 	Root.SetHandler(log15.DiscardHandler())
 }
@@ -115,6 +117,12 @@ func Close() {
 	loggersToClose = make([]DisposableHandler, 0)
 }
 
+func Reload() {
+	for _, logger := range loggersToReload {
+		logger.Reload()
+	}
+}
+
 func GetLogLevelFor(name string) Lvl {
 	if level, ok := filters[name]; ok {
 		switch level {
@@ -230,6 +238,7 @@ func ReadLoggingConfig(modes []string, logsPath string, cfg *ini.File) {
 			fileHandler.Init()
 
 			loggersToClose = append(loggersToClose, fileHandler)
+			loggersToReload = append(loggersToReload, fileHandler)
 			handler = fileHandler
 		case "syslog":
 			sysLogHandler := NewSyslog(sec, format)