Add Environment Variable options to flags managed in exporter-toolkit

README.md

@@ -111,8 +111,8 @@ usage: nginx-prometheus-exporter [<flags>]
 Flags:
   -h, --[no-]help                Show context-sensitive help (also try --help-long and --help-man).
       --web.listen-address=:9113 ...
-                                 Addresses on which to expose metrics and web interface. Repeatable for multiple addresses.
-      --web.config.file=""       Path to configuration file that can enable TLS or authentication. See: https://github.com/prometheus/exporter-toolkit/blob/master/docs/web-configuration.md
+                                 Addresses on which to expose metrics and web interface. Repeatable for multiple addresses. ($LISTEN_ADDRESS)
+      --web.config.file=""       Path to configuration file that can enable TLS or authentication. See: https://github.com/prometheus/exporter-toolkit/blob/master/docs/web-configuration.md ($CONFIG_FILE)
       --web.telemetry-path="/metrics"
                                  Path under which to expose metrics. ($TELEMETRY_PATH)
       --[no-]nginx.plus          Start the exporter for NGINX Plus. By default, the exporter is started for NGINX. ($NGINX_PLUS)

exporter.go

@@ -93,6 +93,13 @@ var (
 
 	// Custom command-line flags
 	timeout = createPositiveDurationFlag(kingpin.Flag("nginx.timeout", "A timeout for scraping metrics from NGINX or NGINX Plus.").Default("5s").Envar("TIMEOUT").HintOptions("5s", "10s", "30s", "1m", "5m"))
+
+	// Flags from external modules which need environment variables added
+	overrideEnvVars = map[string]string{
+		"web.listen-address": "LISTEN_ADDRESS",
+		"web.systemd-socket": "SYSTEMD_SOCKET",
+		"web.config.file":    "CONFIG_FILE",
+	}
 )
 
 const exporterName = "nginx_exporter"
@@ -114,6 +121,15 @@ func main() {
 	flag.AddFlags(kingpin.CommandLine, promlogConfig)
 	kingpin.Version(version.Print(exporterName))
 	kingpin.HelpFlag.Short('h')
+
+	// add environment variable options to flags
+	for k, v := range overrideEnvVars {
+		f := kingpin.CommandLine.GetFlag(k)
+		if f != nil {
+			f.Envar(v)
+		}
+	}
+
 	kingpin.Parse()
 	logger := promlog.New(promlogConfig)