lib/logger: follow-up for 72f8fce107

- Document the change at docs/CHANELOG.md
- Log fatal errors if the -loggerJSONFields contains unexpected values
- Rename -loggerJsonFields to -loggerJSONFields for the sake of consistency naming commonly used in Go

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2348

lib/logger/json-fields.go

@@ -1,32 +0,0 @@
-package logger
-
-import "strings"
-
-var (
-	fieldTs     = "ts"
-	fieldLevel  = "level"
-	fieldCaller = "caller"
-	fieldMsg    = "msg"
-)
-
-func setLoggerJSONFields() {
-	fields := strings.Split(*loggerJSONFields, ",")
-	for _, f := range fields {
-		v := strings.Split(strings.TrimSpace(f), ":")
-		if len(v) != 2 {
-			continue
-		}
-
-		old, new := v[0], v[1]
-		switch old {
-		case "ts":
-			fieldTs = new
-		case "level":
-			fieldLevel = new
-		case "caller":
-			fieldCaller = new
-		case "msg":
-			fieldMsg = new
-		}
-	}
-}

lib/logger/logger.go

@@ -17,11 +17,10 @@ import (
 )
 
 var (
-	loggerLevel      = flag.String("loggerLevel", "INFO", "Minimum level of errors to log. Possible values: INFO, WARN, ERROR, FATAL, PANIC")
-	loggerFormat     = flag.String("loggerFormat", "default", "Format for logs. Possible values: default, json")
-	loggerOutput     = flag.String("loggerOutput", "stderr", "Output for the logs. Supported values: stderr, stdout")
-	loggerJSONFields = flag.String("loggerJsonFields", "", `Allows renaming fields in JSON formatted logs. Example: "ts:timestamp,msg:message" renames "ts" to "timestamp" and "msg" to "message"`)
-	loggerTimezone   = flag.String("loggerTimezone", "UTC", "Timezone to use for timestamps in logs. Timezone must be a valid IANA Time Zone. "+
+	loggerLevel    = flag.String("loggerLevel", "INFO", "Minimum level of errors to log. Possible values: INFO, WARN, ERROR, FATAL, PANIC")
+	loggerFormat   = flag.String("loggerFormat", "default", "Format for logs. Possible values: default, json")
+	loggerOutput   = flag.String("loggerOutput", "stderr", "Output for the logs. Supported values: stderr, stdout")
+	loggerTimezone = flag.String("loggerTimezone", "UTC", "Timezone to use for timestamps in logs. Timezone must be a valid IANA Time Zone. "+
 		"For example: America/New_York, Europe/Berlin, Etc/GMT+3 or Local")
 	disableTimestamps = flag.Bool("loggerDisableTimestamps", false, "Whether to disable writing timestamps in logs")