Add time zone offset metric

Add the time zone and offset in seconds.

Closes: https://github.com/prometheus/node_exporter/issues/2052

Signed-off-by: Ben Kochie <superq@gmail.com>

CHANGELOG.md

@@ -10,6 +10,7 @@ NOTE: Filesystem collector flags have been renamed. `--collector.filesystem.igno
 
 * [CHANGE] Rename filesystem collector flags to match other collectors #2012
 * [FEATURE] Add flag to ignore network speed if it is unknown #1989
+* [ENHANCEMENT] Add time zone offset metric #2060
 * [BUGFIX] Add ErrorLog plumbing to promhttp #1887
   
 ## 1.1.2 / 2021-03-05

collector/time.go

@@ -24,8 +24,9 @@ import (
 )
 
 type timeCollector struct {
-	desc   *prometheus.Desc
-	logger log.Logger
+	nowDesc  *prometheus.Desc
+	zoneDesc *prometheus.Desc
+	logger   log.Logger
 }
 
 func init() {
@@ -35,19 +36,30 @@ func init() {
 // NewTimeCollector returns a new Collector exposing the current system time in
 // seconds since epoch.
 func NewTimeCollector(logger log.Logger) (Collector, error) {
+	const subsystem = "time"
 	return &timeCollector{
-		desc: prometheus.NewDesc(
-			namespace+"_time_seconds",
+		nowDesc: prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, subsystem, "seconds"),
 			"System time in seconds since epoch (1970).",
 			nil, nil,
 		),
+		zoneDesc: prometheus.NewDesc(
+			prometheus.BuildFQName(namespace, subsystem, "zone_offset_seconds"),
+			"System time zone offset in seconds.",
+			[]string{"time_zone"}, nil,
+		),
 		logger: logger,
 	}, nil
 }
 
 func (c *timeCollector) Update(ch chan<- prometheus.Metric) error {
-	now := float64(time.Now().UnixNano()) / 1e9
-	level.Debug(c.logger).Log("msg", "Return time", "now", now)
-	ch <- prometheus.MustNewConstMetric(c.desc, prometheus.GaugeValue, now)
+	now := time.Now()
+	nowSec := float64(now.UnixNano()) / 1e9
+	zone, zoneOffset := now.Zone()
+
+	level.Debug(c.logger).Log("msg", "Return time", "now", nowSec)
+	ch <- prometheus.MustNewConstMetric(c.nowDesc, prometheus.GaugeValue, nowSec)
+	level.Debug(c.logger).Log("msg", "Zone offset", "offset", zoneOffset, "time_zone", zone)
+	ch <- prometheus.MustNewConstMetric(c.zoneDesc, prometheus.GaugeValue, float64(zoneOffset), zone)
 	return nil
 }