etcdmain: add log-output flag

So we can choose where to write logs.
Fix etcd-io#5449.

etcdmain/config.go

@@ -135,6 +135,7 @@ type config struct {
 	// Debug logging
 	Debug        bool   `json:"debug"`
 	LogPkgLevels string `json:"log-package-levels"`
+	LogOutput    string `json:"log-output"`
 
 	// ForceNewCluster is unsafe
 	ForceNewCluster bool `json:"force-new-cluster"`
@@ -249,6 +250,7 @@ func NewConfig() *config {
 	// logging
 	fs.BoolVar(&cfg.Debug, "debug", false, "Enable debug-level logging for etcd.")
 	fs.StringVar(&cfg.LogPkgLevels, "log-package-levels", "", "Specify a particular log level for each etcd package (eg: 'etcdmain=CRITICAL,etcdserver=DEBUG').")
+	fs.StringVar(&cfg.LogOutput, "log-output", "stderr", "Specify log output path (stderr,stdout,journald,YOUR_NAME.log).")
 
 	// unsafe
 	fs.BoolVar(&cfg.ForceNewCluster, "force-new-cluster", false, "Force to create a new one member cluster.")

etcdmain/etcd.go

@@ -24,6 +24,7 @@ import (
 	_ "net/http/pprof"
 	"os"
 	"path"
+	"path/filepath"
 	"reflect"
 	"runtime"
 	"strings"
@@ -616,6 +617,42 @@ func setupLogging(cfg *config) {
 		}
 		repoLog.SetLogLevel(settings)
 	}
+	switch cfg.LogOutput {
+	case "", "stderr":
+		break
+
+	case "stdout":
+		capnslog.SetFormatter(capnslog.NewPrettyFormatter(os.Stdout, cfg.Debug))
+
+	case "journald":
+		f, err := capnslog.NewJournaldFormatter()
+		if err != nil {
+			plog.Warningf("couldn't log to journald (%v)", err)
+			return
+		}
+		capnslog.SetFormatter(f)
+
+	default:
+		if filepath.Ext(cfg.LogOutput) == ".log" {
+			f, err := openToAppend(cfg.LogOutput)
+			if err != nil {
+				plog.Warningf("couldn't log to file %q (%v)", cfg.LogOutput, err)
+				return
+			}
+			capnslog.SetFormatter(capnslog.NewPrettyFormatter(f, cfg.Debug))
+		}
+	}
+}
+
+func openToAppend(fpath string) (*os.File, error) {
+	f, err := os.OpenFile(fpath, os.O_RDWR|os.O_APPEND, fileutil.PrivateFileMode)
+	if err != nil {
+		f, err = os.Create(fpath)
+		if err != nil {
+			return f, err
+		}
+	}
+	return f, nil
 }
 
 func checkSupportArch() {

etcdmain/help.go

@@ -131,6 +131,8 @@ logging flags
 		enable debug-level logging for etcd.
 	--log-package-levels ''
 		specify a particular log level for each etcd package (eg: 'etcdmain=CRITICAL,etcdserver=DEBUG').
+	--log-output 'stderr'
+		specify log output path (stderr,stdout,journald,YOUR_NAME.log).
 
 unsafe flags: