Add envOrDefault call to main.go; handle flags with it

This call simply accepts an environment variable or the default provided
as the *default* to the flag variable. This is intended to be suitable
for 12-factor situations as well as allow the commandline to still
override it.

Signed-off-by: Erik Hollensbe <[email protected]>

Author: Erik Hollensbe

main.go

@@ -68,13 +68,13 @@ func main() {
 		logJSON              bool
 	)
 
-	flag.StringVar(&metricsAddr, "metrics-addr", ":8080", "The address the metric endpoint binds to.")
-	flag.StringVar(&eventsAddr, "events-addr", "", "The address of the events receiver.")
+	flag.StringVar(&metricsAddr, "metrics-addr", envOrDefault("METRICS_ADDR", ":8080"), "The address the metric endpoint binds to.")
+	flag.StringVar(&eventsAddr, "events-addr", envOrDefault("EVENTS_ADDR", ""), "The address of the events receiver.")
 	flag.BoolVar(&enableLeaderElection, "enable-leader-election", false,
 		"Enable leader election for controller manager. "+
 			"Enabling this will ensure there is only one active controller manager.")
-	flag.StringVar(&storagePath, "storage-path", "", "The local storage path.")
-	flag.StringVar(&storageAddr, "storage-addr", ":9090", "The address the static file server binds to.")
+	flag.StringVar(&storagePath, "storage-path", envOrDefault("STORAGE_PATH", ""), "The local storage path.")
+	flag.StringVar(&storageAddr, "storage-addr", envOrDefault("STORAGE_ADDR", ":9090"), "The address the static file server binds to.")
 	flag.IntVar(&concurrent, "concurrent", 2, "The number of concurrent reconciles per controller.")
 	flag.BoolVar(&logJSON, "log-json", false, "Set logging to JSON format.")
 
@@ -190,3 +190,12 @@ func mustInitStorage(path string, storageAddr string, l logr.Logger) *controller
 
 	return storage
 }
+
+func envOrDefault(envName, dflt string) string {
+	ret := os.Getenv(envName)
+	if ret != "" {
+		return ret
+	}
+
+	return dflt
+}