fix: use a flag for the configuration file

Author: Noah Perks Sloan

docs/customresourcestate-metrics.md

@@ -5,7 +5,11 @@ registry and running your own build of KSM.
 
 ## Configuration
 
-The `KSM_CUSTOM_RESOURCE_METRICS` environment variable can be used to configure the metrics for custom resources:
+A configuration file is required to describe your custom resources and the fields to turn into metrics.
+
+The contents of this file can be set as an environment variable, `KSM_CUSTOM_RESOURCE_METRICS`, or the 
+flag `--custom-resource-state-config=/path/to/config.yaml` can be used to specify a file on the filesystem. 
+The command flag takes precedence over the environment variable. e.g.,
 
 ```yaml
 apiVersion: apps/v1

main.go

@@ -52,7 +52,7 @@ func main() {
 	}
 
 	var factories []customresource.RegistryFactory
-	if config, set := resolveCustomResourceConfig(); set {
+	if config, set := resolveCustomResourceConfig(opts); set {
 		crf, err := customresourcestate.FromConfig(config)
 		if err != nil {
 			klog.Fatal(err)
@@ -66,16 +66,16 @@ func main() {
 	}
 }
 
-func resolveCustomResourceConfig() (customresourcestate.ConfigDecoder, bool) {
-	if s, set := os.LookupEnv("KSM_CUSTOM_RESOURCE_METRICS"); set {
-		return yaml.NewDecoder(strings.NewReader(s)), true
-	}
-	if file, set := os.LookupEnv("KSM_CUSTOM_RESOURCE_METRICS_FILE"); set {
+func resolveCustomResourceConfig(opts *options.Options) (customresourcestate.ConfigDecoder, bool) {
+	if file := opts.CustomResourceConfigFile; file != "" {
 		f, err := os.Open(file)
 		if err != nil {
 			klog.Fatal(err)
 		}
 		return yaml.NewDecoder(f), true
 	}
+	if s, set := os.LookupEnv("KSM_CUSTOM_RESOURCE_METRICS"); set {
+		return yaml.NewDecoder(strings.NewReader(s)), true
+	}
 	return nil, false
 }

pkg/options/options.go

@@ -54,6 +54,8 @@ type Options struct {
 
 	UseAPIServerCache bool
 
+	CustomResourceConfigFile string
+
 	flags *pflag.FlagSet
 }
 
@@ -111,6 +113,8 @@ func (o *Options) AddFlags() {
 	o.flags.StringVar(&o.Namespace, "pod-namespace", "", "Name of the namespace of the pod specified by --pod. "+autoshardingNotice)
 	o.flags.BoolVarP(&o.Version, "version", "", false, "kube-state-metrics build version information")
 	o.flags.BoolVar(&o.EnableGZIPEncoding, "enable-gzip-encoding", false, "Gzip responses when requested by clients via 'Accept-Encoding: gzip' header.")
+
+	o.flags.StringVar(&o.CustomResourceConfigFile, "custom-resource-state-config", "", "Path to a Custom Resource State Metrics config file")
 }
 
 // Parse parses the flag definitions from the argument list.