pkg/logutil: error when it can't find journal socket

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

pkg/logutil/zap_journald.go

@@ -24,6 +24,8 @@ import (
 	"os"
 	"path/filepath"
 
+	"github.com/coreos/etcd/pkg/systemd"
+
 	"github.com/coreos/go-systemd/journal"
 	"go.uber.org/zap/zapcore"
 )
@@ -33,8 +35,8 @@ import (
 // back to writing to the original writer.
 // The decode overhead is only <30µs per write.
 // Reference: https://github.com/coreos/pkg/blob/master/capnslog/journald_formatter.go
-func NewJournaldWriter(wr io.Writer) io.Writer {
-	return &journaldWriter{Writer: wr}
+func NewJournaldWriter(wr io.Writer) (io.Writer, error) {
+	return &journaldWriter{Writer: wr}, systemd.DialJournal()
 }
 
 type journaldWriter struct {
@@ -82,6 +84,8 @@ func (w *journaldWriter) Write(p []byte) (int, error) {
 		"SYSLOG_IDENTIFIER": filepath.Base(os.Args[0]),
 	})
 	if err != nil {
+		// "journal" also falls back to stderr
+		// "fmt.Fprintln(os.Stderr, s)"
 		return w.Writer.Write(p)
 	}
 	return 0, nil

pkg/logutil/zap_journald_test.go

@@ -26,7 +26,13 @@ import (
 
 func TestNewJournaldWriter(t *testing.T) {
 	buf := bytes.NewBuffer(nil)
-	syncer := zapcore.AddSync(NewJournaldWriter(buf))
+	jw, err := NewJournaldWriter(buf)
+	if err != nil {
+		t.Skip(err)
+	}
+
+	syncer := zapcore.AddSync(jw)
+
 	cr := zapcore.NewCore(
 		zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
 		syncer,

pkg/systemd/doc.go

@@ -0,0 +1,16 @@
+// Copyright 2018 The etcd 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 systemd provides utility functions for systemd.
+package systemd

pkg/systemd/journal.go

@@ -0,0 +1,29 @@
+// Copyright 2018 The etcd 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 systemd
+
+import "net"
+
+// DialJournal returns no error if the process can dial journal socket.
+// Returns an error if dial failed, whichi indicates journald is not available
+// (e.g. run embedded etcd as docker daemon).
+// Reference: https://github.com/coreos/go-systemd/blob/master/journal/journal.go.
+func DialJournal() error {
+	conn, err := net.Dial("unixgram", "/run/systemd/journal/socket")
+	if conn != nil {
+		defer conn.Close()
+	}
+	return err
+}