Make it possible to override config options from command line

Implement new '--options' command line flag that can be used to specify
config options from command line. Options specified via this command
line flag will override those read from the config file. The same format
as in the config file must be used, that is, the flag value must be
valid YAML or JSON.

README.md

@@ -39,6 +39,7 @@ node-feature-discovery.
   Usage:
   node-feature-discovery [--no-publish] [--sources=<sources>] [--label-whitelist=<pattern>]
      [--oneshot | --sleep-interval=<seconds>] [--config=<path>]
+     [--options=<config>]
   node-feature-discovery -h | --help
   node-feature-discovery --version
 
@@ -47,6 +48,11 @@ node-feature-discovery.
   --version                   Output version and exit.
   --config=<path>             Config file to use.
                               [Default: /etc/kubernetes/node-feature-discovery/node-feature-discovery.conf]
+  --options=<config>          Specify config options from command line. Config
+                              options are specified in the same format as in the
+                              config file (i.e. json or yaml). These options
+                              will override settings read from the config file.
+                              [Default: ]
   --sources=<sources>         Comma separated list of feature sources.
                               [Default: cpuid,iommu,memory,network,pstate,rdt,selinux,storage]
   --no-publish                Do not publish discovered features to the
@@ -233,7 +239,7 @@ For example, if some node is tainted NoSchedule or fails to start a job for some
 
 [![asciicast](https://asciinema.org/a/11wir751y89617oemwnsgli4a.png)](https://asciinema.org/a/11wir751y89617oemwnsgli4a)
 
-### Configuration file
+### Configuration options
 
 NFD supports a configuration file. The default location is
 `/etc/kubernetes/node-feature-discovery/node-feature-discovery.conf`, but,
@@ -267,9 +273,16 @@ different config for different nodes would be required, for example.
 
 The (empty-by-default)
 [example config](https://github.com/kubernetes-incubator/node-feature-discovery/blob/master/node-feature-discovery.conf.example)
-is used as a config in the NFD Docker image. Thus, this can be used as default
+is used as a config in the NFD Docker image. Thus, this can be used as a default
 configuration in custom-built images.
 
+Configuration options can also be specified via the `--options` command line
+flag, in which case no mounts need to be used. The same format as in the config
+file must be used, i.e. JSON (or YAML).
+
+Configuration options specified from the command line will override those read
+from the config file.
+
 ## Building from source
 
 Download the source code.

main.go

@@ -88,6 +88,7 @@ type Args struct {
 	labelWhiteList string
 	configFile     string
 	noPublish      bool
+	options        string
 	oneshot        bool
 	sleepInterval  time.Duration
 	sources        []string
@@ -102,8 +103,8 @@ func main() {
 	// Parse command-line arguments.
 	args := argsParse(nil)
 
-	// Read the config file
-	err := configParse(args.configFile)
+	// Parse config
+	err := configParse(args.configFile, args.options)
 	if err != nil {
 		stderrLogger.Print(err)
 	}
@@ -147,6 +148,7 @@ func argsParse(argv []string) (args Args) {
   Usage:
   %s [--no-publish] [--sources=<sources>] [--label-whitelist=<pattern>]
      [--oneshot | --sleep-interval=<seconds>] [--config=<path>]
+     [--options=<config>]
   %s -h | --help
   %s --version
 
@@ -155,6 +157,11 @@ func argsParse(argv []string) (args Args) {
   --version                   Output version and exit.
   --config=<path>             Config file to use.
                               [Default: /etc/kubernetes/node-feature-discovery/node-feature-discovery.conf]
+  --options=<config>          Specify config options from command line. Config
+                              options are specified in the same format as in the
+                              config file (i.e. json or yaml). These options
+                              will override settings read from the config file.
+                              [Default: ]
   --sources=<sources>         Comma separated list of feature sources.
                               [Default: cpuid,iommu,memory,network,pstate,rdt,selinux,storage]
   --no-publish                Do not publish discovered features to the
@@ -178,6 +185,7 @@ func argsParse(argv []string) (args Args) {
 	var err error
 	args.configFile = arguments["--config"].(string)
 	args.noPublish = arguments["--no-publish"].(bool)
+	args.options = arguments["--options"].(string)
 	args.sources = strings.Split(arguments["--sources"].(string), ",")
 	args.labelWhiteList = arguments["--label-whitelist"].(string)
 	args.oneshot = arguments["--oneshot"].(bool)
@@ -195,8 +203,8 @@ func argsParse(argv []string) (args Args) {
 	return args
 }
 
-// Parse configuration file
-func configParse(filepath string) error {
+// Parse configuration options
+func configParse(filepath string, overrides string) error {
 	data, err := ioutil.ReadFile(filepath)
 	if err != nil {
 		return fmt.Errorf("Failed to read config file: %s", err)
@@ -208,6 +216,12 @@ func configParse(filepath string) error {
 		return fmt.Errorf("Failed to parse config file: %s", err)
 	}
 
+	// Parse config overrides
+	err = yaml.Unmarshal([]byte(overrides), &config)
+	if err != nil {
+		return fmt.Errorf("Failed to parse --options: %s", err)
+	}
+
 	return nil
 }
 

main_test.go

@@ -179,7 +179,7 @@ func TestArgsParse(t *testing.T) {
 func TestConfigParse(t *testing.T) {
 	Convey("When parsing configuration file", t, func() {
 		Convey("When non-accessible file is given", func() {
-			err := configParse("non-existing-file")
+			err := configParse("non-existing-file", "")
 
 			Convey("Should return error", func() {
 				So(err, ShouldNotBeNil)
@@ -193,7 +193,7 @@ func TestConfigParse(t *testing.T) {
 		f.Close()
 
 		Convey("When proper config file is given", func() {
-			err := configParse(f.Name())
+			err := configParse(f.Name(), "")
 
 			Convey("Should return error", func() {
 				So(err, ShouldBeNil)