Add -logfile and -nostdout flags for logging

This commit adds two flags:
* -logfile, to enable logging to file as additional destination
* -nostdout, to disable logging to stdout

Disabing logging to stdout can help improving QPS in certain setups.

Signed-off-by: Andrea Barberio <insomniac@slackware.it>

cmds/coredhcp/main.go

@@ -5,6 +5,7 @@
 package main
 
 import (
+	"flag"
 	"time"
 
 	"github.com/coredhcp/coredhcp"
@@ -18,18 +19,32 @@ import (
 	_ "github.com/coredhcp/coredhcp/plugins/server_id"
 )
 
+var (
+	flagLogFile     = flag.String("logfile", "", "Name of the log file to append to. Default: stdout/stderr only")
+	flagLogNoStdout = flag.Bool("nostdout", false, "Disable logging to stdout/stderr")
+)
+
 func main() {
-	logger := logger.GetLogger("main")
+	flag.Parse()
+	log := logger.GetLogger("main")
+	if *flagLogFile != "" {
+		log.Infof("Logging to file %s", *flagLogFile)
+		logger.WithFile(log, *flagLogFile)
+	}
+	if *flagLogNoStdout {
+		log.Infof("Disabling logging to stdout/stderr")
+		logger.WithNoStdOutErr(log)
+	}
 	config, err := config.Load()
 	if err != nil {
-		logger.Fatal(err)
+		log.Fatal(err)
 	}
 	server := coredhcp.NewServer(config)
 	if err := server.Start(); err != nil {
-		logger.Fatal(err)
+		log.Fatal(err)
 	}
 	if err := server.Wait(); err != nil {
-		logger.Print(err)
+		log.Error(err)
 	}
 	time.Sleep(time.Second)
 }

go.mod

@@ -12,6 +12,7 @@ require (
 	github.com/mgutz/ansi v0.0.0-20170206155736-9520e82c474b // indirect
 	github.com/onsi/ginkgo v1.9.0 // indirect
 	github.com/onsi/gomega v1.6.0 // indirect
+	github.com/rifflock/lfshook v0.0.0-20180920164130-b9218ef580f5
 	github.com/sirupsen/logrus v1.4.2
 	github.com/spf13/cast v1.3.0
 	github.com/spf13/viper v1.4.0

go.sum

@@ -100,6 +100,8 @@ github.com/prometheus/common v0.4.0/go.mod h1:TNfzLD0ON7rHzMJeJkieUDPYmFC7Snx/y8
 github.com/prometheus/procfs v0.0.0-20181005140218-185b4288413d/go.mod h1:c3At6R/oaqEKCNdg8wHV1ftS6bRYblBhIjjI8uT2IGk=
 github.com/prometheus/procfs v0.0.0-20190507164030-5867b95ac084/go.mod h1:TjEm7ze935MbeOT/UhFTIMYKhuLP4wbCsTZCD3I8kEA=
 github.com/prometheus/tsdb v0.7.1/go.mod h1:qhTCs0VvXwvX/y3TZrWD7rabWM+ijKTux40TwIPHuXU=
+github.com/rifflock/lfshook v0.0.0-20180920164130-b9218ef580f5 h1:mZHayPoR0lNmnHyvtYjDeq0zlVHn9K/ZXoy17ylucdo=
+github.com/rifflock/lfshook v0.0.0-20180920164130-b9218ef580f5/go.mod h1:GEXHk5HgEKCvEIIrSpFI3ozzG5xOKA2DVlEX/gGnewM=
 github.com/rogpeppe/fastuuid v0.0.0-20150106093220-6724a57986af/go.mod h1:XWv6SoW27p1b0cqNHllgS5HIMJraePCO15w5zCzIWYg=
 github.com/sirupsen/logrus v1.2.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=
 github.com/sirupsen/logrus v1.4.2 h1:SPIRibHv4MatM3XXNO2BJeFLZwZ2LvZgfQ5+UNI2im4=

logger/logger.go

@@ -5,9 +5,11 @@
 package logger
 
 import (
+	"io/ioutil"
 	"sync"
 
 	log_prefixed "github.com/chappjc/logrus-prefix"
+	"github.com/rifflock/lfshook"
 	"github.com/sirupsen/logrus"
 )
 
@@ -32,3 +34,13 @@ func GetLogger(prefix string) *logrus.Entry {
 	}
 	return globalLogger.WithField("prefix", prefix)
 }
+
+// WithFile logs to the specified file in addition to the existing output.
+func WithFile(log *logrus.Entry, logfile string) {
+	log.Logger.AddHook(lfshook.NewHook(logfile, &logrus.TextFormatter{}))
+}
+
+// WithNoStdOutErr disables logging to stdout/stderr.
+func WithNoStdOutErr(log *logrus.Entry) {
+	log.Logger.SetOutput(ioutil.Discard)
+}