refactor: inline config as a flag

This is more flexible than the env variable, as a configuration can still set an env variable and use substitution in the args. e.g.,

```yaml
args:
 - --custom-resource-state.config
 - $(KSM_CUSTOM_RESOURCE_STATE_CONFIG)
env:
 ...
```

Author: Noah Perks Sloan

docs/customresourcestate-metrics.md

@@ -5,11 +5,14 @@ registry and running your own build of KSM.
 
 ## Configuration
 
-A configuration file is required to describe your custom resources and the fields to turn into metrics.
+A YAML configuration file described below is required to define 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.,
+Two flags can be used:
+
+ * `--custom-resource-state.config "inline yaml (see example)"` or
+ * `--custom-resource-state-config /path/to/config.yaml`
+
+If both flags are provided, the inline configuration will take precedence.
 
 ```yaml
 apiVersion: apps/v1
@@ -22,9 +25,11 @@ spec:
     spec:
       containers:
       - name: kube-state-metrics
-        env:
-          - name: KSM_CUSTOM_RESOURCE_METRICS
-            value: |
+        args:
+          - --custom-resource-state.config
+          # in YAML files, | allows a multi-line string to be passed as a flag value
+          # see https://yaml-multiline.info
+          -  |
               spec:
                 resources:
                   - groupVersionKind:
@@ -79,6 +84,8 @@ status:
 
 #### Single Values
 
+The config:
+
 ```yaml
 kind: CustomResourceStateMetrics
 spec:
@@ -153,7 +160,7 @@ kube_myteam_io_v1_Foo_active_count{active="3",custom_metric="yes",foo="bar",name
 ### Naming
 
 The default metric names are prefixed to avoid collisions with other metrics.
-By default a namespace of `kube` and a subsystem based on your custom resource's group+version+kind is used.
+By default, a namespace of `kube` and a subsystem based on your custom resource's group+version+kind is used.
 You can override these with the namespace and subsystem fields.
 
 ```yaml

main.go

@@ -67,15 +67,15 @@ func main() {
 }
 
 func resolveCustomResourceConfig(opts *options.Options) (customresourcestate.ConfigDecoder, bool) {
+	if s := opts.CustomResourceConfig; s != "" {
+		return yaml.NewDecoder(strings.NewReader(s)), true
+	}
 	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 +54,7 @@ type Options struct {
 
 	UseAPIServerCache bool
 
+	CustomResourceConfig     string
 	CustomResourceConfigFile string
 
 	flags *pflag.FlagSet
@@ -114,7 +115,8 @@ func (o *Options) AddFlags() {
 	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")
+	o.flags.StringVar(&o.CustomResourceConfig, "custom-resource-state.config", "", "Inline Custom Resource State Metrics config YAML")
+	o.flags.StringVar(&o.CustomResourceConfigFile, "custom-resource-state.config-file", "", "Path to a Custom Resource State Metrics config file")
 }
 
 // Parse parses the flag definitions from the argument list.