Config Option to Enable Logging with Local Time (influxdata#9123)

* Configurable local time logging

* make timezone configurable

* Address linter feedback.

* update with example

cmd/telegraf/telegraf.go

@@ -174,6 +174,7 @@ func runAgent(ctx context.Context,
 		RotationInterval:    ag.Config.Agent.LogfileRotationInterval,
 		RotationMaxSize:     ag.Config.Agent.LogfileRotationMaxSize,
 		RotationMaxArchives: ag.Config.Agent.LogfileRotationMaxArchives,
+		LogWithTimezone:     ag.Config.Agent.LogWithTimezone,
 	}
 
 	logger.SetupLogging(logConfig)

config/config.go

@@ -188,6 +188,9 @@ type AgentConfig struct {
 	// If set to -1, no archives are removed.
 	LogfileRotationMaxArchives int `toml:"logfile_rotation_max_archives"`
 
+	// Pick a timezone to use when logging or type 'local' for local time.
+	LogWithTimezone string `toml:"log_with_timezone"`
+
 	Hostname     string
 	OmitHostname bool
 }
@@ -356,11 +359,14 @@ var agentConfig = `
   ## If set to -1, no archives are removed.
   # logfile_rotation_max_archives = 5
 
+  ## Pick a timezone to use when logging or type 'local' for local time.
+  ## Example: America/Chicago
+  # log_with_timezone = ""
+
   ## Override default hostname, if empty use os.Hostname()
   hostname = ""
   ## If set to true, do no set the "host" tag in the telegraf agent.
   omit_hostname = false
-
 `
 
 var outputHeader = `

docs/CONFIGURATION.md

@@ -219,6 +219,10 @@ The agent table configures Telegraf and the defaults used across all plugins.
   Maximum number of rotated archives to keep, any older logs are deleted.  If
   set to -1, no archives are removed.
 
+- **log_with_timezone**:
+  Pick a timezone to use when logging or type 'local' for local time. Example: 'America/Chicago'.
+  [See this page for options/formats.](https://socketloop.com/tutorials/golang-display-list-of-timezones-with-gmt)
+
 - **hostname**:
   Override default hostname, if empty use os.Hostname()
 - **omit_hostname**:

etc/telegraf.conf

@@ -90,6 +90,10 @@
   ## If set to -1, no archives are removed.
   # logfile_rotation_max_archives = 5
 
+  ## Pick a timezone to use when logging or type 'local' for local time. Example: 'America/Chicago'.
+  ## See https://socketloop.com/tutorials/golang-display-list-of-timezones-with-gmt for timezone formatting options.
+  # log_with_timezone = ""
+
   ## Override default hostname, if empty use os.Hostname()
   hostname = ""
   ## If set to true, do no set the "host" tag in the telegraf agent.

etc/telegraf_windows.conf

@@ -90,6 +90,10 @@
   ## If set to -1, no archives are removed.
   # logfile_rotation_max_archives = 5
 
+  ## Pick a timezone to use when logging or type 'local' for local time. Example: 'America/Chicago'.
+  ## See https://socketloop.com/tutorials/golang-display-list-of-timezones-with-gmt for timezone formatting options.
+  # log_with_timezone = ""
+
   ## Override default hostname, if empty use os.Hostname()
   hostname = ""
   ## If set to true, do no set the "host" tag in the telegraf agent.

logger/logger.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"os"
 	"regexp"
+	"strings"
 	"time"
 
 	"github.com/influxdata/telegraf/config"
@@ -38,6 +39,8 @@ type LogConfig struct {
 	RotationMaxSize config.Size
 	// maximum rotated files to keep (older ones will be deleted)
 	RotationMaxArchives int
+	// pick a timezone to use when logging. or type 'local' for local time.
+	LogWithTimezone string
 }
 
 type LoggerCreator interface {
@@ -56,15 +59,19 @@ func registerLogger(name string, loggerCreator LoggerCreator) {
 type telegrafLog struct {
 	writer         io.Writer
 	internalWriter io.Writer
+	timezone       *time.Location
 }
 
 func (t *telegrafLog) Write(b []byte) (n int, err error) {
 	var line []byte
+	timeToPrint := time.Now().In(t.timezone)
+
 	if !prefixRegex.Match(b) {
-		line = append([]byte(time.Now().UTC().Format(time.RFC3339)+" I! "), b...)
+		line = append([]byte(timeToPrint.Format(time.RFC3339)+" I! "), b...)
 	} else {
-		line = append([]byte(time.Now().UTC().Format(time.RFC3339)+" "), b...)
+		line = append([]byte(timeToPrint.Format(time.RFC3339)+" "), b...)
 	}
+
 	return t.writer.Write(line)
 }
 
@@ -82,11 +89,23 @@ func (t *telegrafLog) Close() error {
 }
 
 // newTelegrafWriter returns a logging-wrapped writer.
-func newTelegrafWriter(w io.Writer) io.Writer {
+func newTelegrafWriter(w io.Writer, c LogConfig) (io.Writer, error) {
+	timezoneName := c.LogWithTimezone
+
+	if strings.ToLower(timezoneName) == "local" {
+		timezoneName = "Local"
+	}
+
+	tz, err := time.LoadLocation(timezoneName)
+	if err != nil {
+		return nil, errors.New("error while setting logging timezone: " + err.Error())
+	}
+
 	return &telegrafLog{
 		writer:         wlog.NewWriter(w),
 		internalWriter: w,
-	}
+		timezone:       tz,
+	}, nil
 }
 
 // SetupLogging configures the logging output.
@@ -119,7 +138,7 @@ func (t *telegrafLogCreator) CreateLogger(config LogConfig) (io.Writer, error) {
 		writer = defaultWriter
 	}
 
-	return newTelegrafWriter(writer), nil
+	return newTelegrafWriter(writer, config)
 }
 
 // Keep track what is actually set as a log output, because log package doesn't provide a getter.

logger/logger_test.go

@@ -137,7 +137,10 @@ func TestLogTargetSettings(t *testing.T) {
 func BenchmarkTelegrafLogWrite(b *testing.B) {
 	var msg = []byte("test")
 	var buf bytes.Buffer
-	w := newTelegrafWriter(&buf)
+	w, err := newTelegrafWriter(&buf, LogConfig{})
+	if err != nil {
+		panic("Unable to create log writer.")
+	}
 	for i := 0; i < b.N; i++ {
 		buf.Reset()
 		w.Write(msg)