lib/httpserver: add is_set label to flag metrics

This label allows determining the set flags with the query `flag{is_set="true"}`

docs/CHANGELOG.md

@@ -15,6 +15,7 @@ sort: 15
   * `/select/<accountID>/vmui/` for `vmselect` at cluster version of VictoriaMetrics
 * FEATURE: support durations anywhere in [MetricsQL queries](https://docs.victoriametrics.com/MetricsQL.html). For example, `sum_over_time(m[1h]) / 1h` is a valid query, which is equivalent to `sum_over_time(m[1h]) / 3600`.
 * FEATURE: support durations without suffxies in [MetricsQL queries](https://docs.victoriametrics.com/MetricsQL.html). For example, `rate(m[3600])` is a valid query, which is equivalent to `rate(m[1h])`.
+* FEATURE: add `is_set` label to `flag` metrics. This allows determining explicitly set command-line flags with the query `flag{is_set="true"}`.
 
 * BUGFIX: vmagent: remove `{ %space %}` typo in `/targets` output. The typo has been introduced in v1.62.0. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1408).
 * BUGFIX: vmagent: fix CSS styles on `/targets` page. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1422).

lib/httpserver/metrics.go

@@ -58,6 +58,10 @@ func writePrometheusMetrics(w io.Writer) {
 	fmt.Fprintf(w, "vm_app_uptime_seconds %d\n", int(time.Since(startTime).Seconds()))
 
 	// Export flags as metrics.
+	isSetMap := make(map[string]bool)
+	flag.Visit(func(f *flag.Flag) {
+		isSetMap[f.Name] = true
+	})
 	flag.VisitAll(func(f *flag.Flag) {
 		lname := strings.ToLower(f.Name)
 		value := f.Value.String()
@@ -65,7 +69,11 @@ func writePrometheusMetrics(w io.Writer) {
 			// Do not expose passwords and keys to prometheus.
 			value = "secret"
 		}
-		fmt.Fprintf(w, "flag{name=%q, value=%q} 1\n", f.Name, value)
+		isSet := "false"
+		if isSetMap[f.Name] {
+			isSet = "true"
+		}
+		fmt.Fprintf(w, "flag{name=%q, value=%q, is_set=%q} 1\n", f.Name, value, isSet)
 	})
 }
 

lib/logger/flag.go

@@ -11,12 +11,20 @@ import (
 func logAllFlags() {
 	Infof("build version: %s", buildinfo.Version)
 	Infof("command line flags")
+	isSetMap := make(map[string]bool)
+	flag.Visit(func(f *flag.Flag) {
+		isSetMap[f.Name] = true
+	})
 	flag.VisitAll(func(f *flag.Flag) {
 		lname := strings.ToLower(f.Name)
 		value := f.Value.String()
 		if flagutil.IsSecretFlag(lname) {
 			value = "secret"
 		}
-		Infof("flag %q = %q", f.Name, value)
+		isSet := "false"
+		if isSetMap[f.Name] {
+			isSet = "true"
+		}
+		Infof("flag %q=%q (is_set=%s)", f.Name, value, isSet)
 	})
 }